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ENSA M2 Single Area OSPFv2 Configuration — Transcript

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0:04hi
0:05hello there welcome to single area ospf
0:08version 2 configuration
0:11now that you know about single area ospf
0:13version 2
0:15you can probably think of all the ways
0:17it could benefit your own network
0:20so as a state link protocol ospf
0:23is designed to not only find the fastest
0:26available route
0:27it is designed to create fast
0:31available route so if you prefer a bit
0:35of more control over some areas of your
0:38network
0:39ospf gives you several ways to manually
0:42override the drl action process
0:44and create your own preferred routes
0:48so with ospf your network can combine
0:52the automated process with your own
0:54choices to make a network that you could
0:56troubleshoot
0:58in your slip all right so you know
1:02you want to learn about this so let's
1:05get it on
1:08all right so for the module objectives
1:11so
1:12this topic or video lecture covers the
1:14single area ospf version to
1:16configuration
1:18so the objective would be at the end of
1:20this video lecture
1:21so you should be able to implement a
1:23single area ospf version 2
1:26in both point-to-point and broadcast
1:29multi-access network
1:31so sub-topics included on this video
1:34lectures are
1:35ospf router id the point-to-point ospf
1:39networks
1:40the multi-access ospf networks
1:44modify single area ospf version 2
1:47the default propagation and verify
1:51single area ospf version 2.
1:56all right so let's start with the first
1:59section
1:59so let's talk about the ospf router id
2:06okay so this would be our ospf reference
2:09topology
2:10so this will be utilized
2:13throughout the discussion okay so to get
2:17you understand not to get started
2:20this topic discusses the foundation of
2:22which ospf
2:24bases its enter process the ospf router
2:27id
2:28so the figure here shows the topology
2:31used
2:32for configuring ospf version 2 in this
2:34module
2:35so the routers in the topology have a
2:37starting configuration
2:39including interface addresses there is
2:42currently no static routing or dynamic
2:44routing configured on any of these
2:46routers
2:47so all interfaces on r1 r2 and r3
2:51except the loopback on r2 are within the
2:54ospf backbone
2:56okay so when you say backbone we're
3:00talking about
3:01area 0. so the isp router is used as a
3:04gateway to the internet
3:06of the routing domain okay
3:10so take note that on this topology the
3:13loopback interface is used
3:14to simulate a one okay or a one link to
3:18the internet
3:19and a line connected to each router so
3:22this is done to allow this topology to
3:24be duplicated
3:25for demonstration purposes and routers
3:28that only have
3:29two gigabit ethernet interfaces
3:35okay so router configuration mode for
3:39ospf so ospf version 2
3:43is enabled using the router ospf
3:46process id global configuration mode
3:48command
3:50so as shown in here so this is for r1
3:54here
3:54okay so the process id value represents
3:58the number between one to sixty five
4:00thousand five hundred thirty five so you
4:02can use
4:02any number within that range and is
4:05selected
4:06by the network administrator so the
4:09process id
4:11is locally significant which means
4:15that it does not have to be the same
4:18value
4:19on the other ospf routers to establish
4:22adjacencies
4:23with those neighbors so it is considered
4:26best practice to use the same process id
4:30on all the ospf routers okay
4:33now after entering the router ospf
4:38process id command as shown here so the
4:41router enters
4:42router configuration mode so as
4:44indicated by
4:46you've got r1 here config and then
4:49you've got the router
4:50okay so this this would be the prompt so
4:53enter a question mark
4:55okay so to view all the commands
4:57available in this mode
4:59so the list of commands shown here
5:02has been altered to display only the
5:04commands that are relevant
5:06to this module right
5:10okay so let's talk about the router id
5:14so an ospf router id is a 32-bit
5:18represented as an ipv4 address
5:21so the router id is used to uniquely
5:23identify an ospf router
5:26so all ospf packets include
5:29the router id of the originating router
5:32so every router requires a router id
5:36to participate in an ospf domain
5:39so the router id can be defined by an
5:42administrator or automatically assigned
5:45by the router
5:46so the router id is used by an ospf
5:49enabled router
5:51to do the following first participate in
5:54the synchronization of the ospf
5:57databases
5:58so during the exchange state the router
6:01with the highest router id
6:03will send their database description
6:06all right or the database descriptor or
6:08dvd packets
6:09first okay so
6:12next would be participate in the
6:15election
6:16of the designated router or dr
6:19so in a multi-access lan environment
6:22the router with the highest router id is
6:25elected the dr
6:27so the routing device where the second
6:29highest router id is elected as
6:32the backup designated router or bdr
6:36so the router that is not considered
6:40a dr or bdr is known to be a daughter's
6:44okay so take note that dr and bdr
6:47election is discussed in more detail
6:51later in this module
6:56okay so how about the router id order of
6:59precedence
7:00okay so but how does this router id
7:03determine
7:04the router id okay so as illustrated in
7:07the figure
7:09okay so cisco routers derived the router
7:12id
7:13based on one of the three criteria
7:16so that is in the following preferential
7:19order
7:20so first the router id is explicitly
7:24configured
7:25using the ospf router id
7:29rid router configuration mode command
7:32so the rid value is any 32-bit
7:35value expressed as an ipv4 address
7:40so this is the recommendation method to
7:42assign a router id
7:45okay second if the router id
7:48is not explicitly configured the router
7:51chooses the highest
7:53ipv4 address of any configured loopback
7:57interfaces
7:59okay so this is the next best
8:02alternative
8:03to assigning a router id
8:06okay so the third one would be if no
8:09loopback interfaces are configured then
8:12the router chooses the highest
8:13active ipv4 address of any of its
8:17physical interfaces all right
8:20so this is the least recommended method
8:24because it makes it more difficult for
8:27administrators
8:28to distinguish between specific routers
8:31now as shown here in the diagram so this
8:33summarizes what i have discussed
8:36okay so router id explicitly configured
8:39if yes
8:40that would be used as a router id so
8:43if not then the router will look for the
8:46loopback
8:47if the administrator has configured any
8:49lookback on the router
8:51and that would be used as the router id
8:54now assuming
8:55if you have multiple loopback configured
8:57in the router so
8:58the router will choose the highest ip
9:02address
9:02assigned to the loopback right
9:05now if in case you did not defined
9:09the router id okay nor
9:12the loopback interfaces then the router
9:16will choose
9:17the highest active ip address
9:20on the interface router okay
9:23so there is no instance that the router
9:26won't have error id
9:30okay next so how do we configure
9:35a loopback interface as the router id
9:38so in the reference topology presented
9:40earlier
9:41only the physical interfaces are
9:43configured and active
9:45so the loopback interfaces have not been
9:48configured so when ospf routing
9:52is enabled on the router the routers
9:54would pick
9:55the following highest active configured
9:58ipv4 address
9:59as the router id okay so
10:04if you are going to go back to our
10:06topology we'll have
10:08r1 r2 and r3 there okay
10:11so note that ospf does not need to be
10:15enabled in an interface
10:17for that interface to be chosen as the
10:19router id
10:21okay so instead of relying on a physical
10:25interface
10:26the router id can be assigned to a
10:28loopback interface
10:30so typically the ipv4
10:33address of this type of loopback
10:35interface
10:36should be configured using a 32-bit
10:39subnet mask
10:40okay so that is 255 the 255-255
10:45that so this effectively creates
10:49a host route so a 32-bit
10:52host route would not get advertised
10:55as a route to other ospf browsers
10:59okay now the example shows how to
11:02configure
11:03a loopback interface on r1 okay so
11:05interface
11:06loopback number okay so assuming that
11:09the router id was not explicitly
11:11configured
11:12or previously learned r1 will use the
11:15ipv4 address
11:171.1.1.1 as its router id
11:22all right so assume r1 has not yet
11:24learned
11:25a router id right so you can verify
11:30what the router id is of a router using
11:33the command show ib
11:34protocols so in there you can see the
11:36router id
11:38and in this case so we did not configure
11:43manually or explicitly a router id
11:46then after we configured a loopback that
11:49would be fetched as a router id
11:52okay next
11:56so in the figure
11:59so the topology has been updated to show
12:01that our id for each of the router
12:03so r1 uses 1.1.1
12:06okay so r2 uses 2.2.2
12:11and r3 uses 3.3.3
12:16now we use the router id our id router
12:18configuration mode command
12:20to manually assign a router id in this
12:23example
12:24the router id 1.1.2.1 is assigned to r1
12:28so we use the command show iprotocols
12:31command
12:32to verify the router id for each of the
12:35router here
12:37okay so like what you see here show ivy
12:40protocols
12:40so router id is 1.1.1 for r1
12:45okay so after we explicitly define it as
12:48a router id
12:491.1.1 that one
12:52all right
12:56okay so how do we modify a router id
13:00so after a router selects a router id
13:04an active ospf router does not allow the
13:07router id to be changed
13:09until the router is reloaded or the ospf
13:12process is reset
13:14okay now in the example here for r1
13:18the configured router id has been
13:20removed
13:21and the router is reloaded
13:25all right so how do we reload the router
13:28so you could use the clear ipo spf
13:30process
13:30okay reset all spf configurations or
13:33processes
13:34yes okay and then that's it
13:38all right so notice that the current
13:40router id
13:41is 10 okay dot
13:46that 10.1.1 which is the loopback
13:500 ip address
13:53all right so the router id should then
13:56be
13:571.1.1.1 so therefore r1 is configured
14:00with the command
14:01router id okay 1.1.1.1
14:06now notice how an informational message
14:09appears
14:10starting that the ospf process must be
14:13cleared
14:14or that the router must be reloaded
14:19right so the reason is because r1
14:22already has adjacencies
14:24with other neighbors using the router id
14:2810.10.1.1
14:31so those adjacencies must be
14:34renegotiated
14:36using the new router id with 1.1.1.1
14:41okay so what we're going to do is to use
14:44the
14:45clear ip ospf process command to reset
14:48the adjacencies
14:49now you can then verify the r1 is using
14:52the new router id command
14:54with the show ip protocols command
14:56pipeline okay
14:58so that is to simplify the output right
15:02to display only the router id section
15:05okay so clearing the ospr process
15:08is the preferred method to reset that id
15:12right so take note that the router id
15:14command is the preferred
15:16method however some older versions of
15:19the ios do not recognize the router id
15:22command
15:24okay so aside from the clear ipo spf
15:27process
15:28okay so after all the clearing of the
15:31usb
15:32ospf process and it doesn't take effect
15:35on the router so maybe you could try uh
15:38saving your configuration and
15:40restarting or resetting the router
15:42itself
15:46okay now let's move on to the next
15:48section
15:49so the next section talks about
15:51point-to-point ospf
15:53networks okay
15:57so let's talk about the network command
16:00syntax okay so one type of network that
16:04uses ospf
16:06is the point-to-point network so you can
16:09specify the interfaces that belongs to a
16:11point-to-point network
16:13by configuring the network command
16:16so you can also configure ospf directly
16:19on the interface with the ipo spf
16:22command as you will see later
16:26okay so both commands are used to
16:28determine
16:30which interfaces participate in the
16:32routing process
16:34for an ospf version 2 area so the basic
16:37syntax
16:38for the network command is as follows
16:41okay so you've got router config router
16:44shift
16:45network network address
16:48wildcard mask area and
16:51the area id okay
16:55so the network address wildcard mask
16:58syntax is used to enable
17:00ospf on interfaces
17:03any interfaces on the router that match
17:06the network
17:07address in the network command are
17:10enabled to send and receive
17:11ospf packets so the area area id syntax
17:16refers to ospf area
17:18so when configuring a single area osp of
17:21version 2
17:22the network command must be configured
17:25with the same
17:26area id value on all routers
17:30okay so although any area id can be used
17:35it is a good practice to use an area id
17:38of zero
17:39with single area or spf version two
17:43okay so this is in convention okay
17:46making it easier if the network is
17:49later altered to support the multi-area
17:52ospf version
17:57all right so how about the wildcard mask
18:01okay so the wildcard mask is typically
18:04an inverse of the subnet mask configured
18:06on the interface so in a subnet mask
18:09binary 1 is equal to a match and binary
18:120
18:13is not a match so in a wildcard mask
18:16the reverse is true as shown here
18:20all right so if the subnet mask is
18:24two five five the two five five the two
18:25five five okay
18:29so you have to subtract it from
18:32two five five the two five five the two
18:34five five the two five five
18:36okay so the wild card mask would be
18:40uh 0.0.0.0 it should be zero
18:45okay so
18:49so the wildcard mask bit zero matches
18:52the corresponding bit value
18:54in the address and the wildcard mask bit
18:571
18:57ignores the corresponding bit value in
18:59the address
19:01so the easiest method for calculating a
19:03wildcard mask is to subtract
19:06the subnet or the network subnet mask
19:08from 255
19:09the two five five the two five five the
19:12two five five
19:14okay so as shown forced last twenty
19:16first last 26
19:17subnet masks in the figure
19:22all right so we have here some
19:25[Music]
19:27uh correction on this powerpoint
19:29presentation so if it is just last two
19:31and a six
19:32okay so subnet mask first last 26 would
19:36be
19:37255.255. 255.192
19:42right so subtracting it from
19:46255.255.255.255.
19:49all right so let's do some
19:52adjustment on this power point here okay
19:56so take note if it is last 24
20:00that's two five five the two five five
20:01the two five five that
20:04this should be zero here
20:08all right so subtracting it so therefore
20:11the wildguard mask
20:13first last 24 would be 0.0.0.255 there
20:20all right now first last 26 this should
20:23be
20:24192 here
20:27all right so it should be 192. okay so
20:30just change that to 192 here
20:33this last one is six okay so
20:36that would be okay subtracting it from
20:39two five five to two five five to two
20:40five five
20:41so that would be zero that zero that
20:43zero okay
20:45that all right it should be that
20:4863 okay
20:54that is first last 26 right
21:03okay so let's configure ospf using the
21:06network command
21:07so within the routing configuration mode
21:09there are two types
21:10to identify the interfaces that will
21:13participate
21:14in the ospf version 2 routing process so
21:17the figure shows the reference topology
21:20here
21:21okay now in the first example
21:24the wildcard mask identifies the
21:27interface
21:28based on the network address so any
21:31active interface
21:32that is configured with an ipv4 address
21:36belonging to the network will
21:37participate in the ospf version 2
21:39routing process
21:42okay now in here
21:45referring to these topology or given
21:47topology
21:48and our reference is on r1
21:51right now on r1 so of course
21:55we need to start with router ospf okay
21:58so 10
22:00network 10.10.1.0
22:050.0.0.255 area 0. so this is area 0 here
22:09so all of those should be area 0.
22:13okay now in defining the
22:16ospf so we care only about the directly
22:19connected networks
22:21and if we are going to evaluate r1 okay
22:23so look at r1 here
22:25so there are three networks connected to
22:28it so this would be the first network
22:30this would be the second network and
22:32this would be the third network here
22:34okay so the first network would be
22:3710.10.1.0
22:39which is the loopback zero here
22:42okay next would be 10.1.1.4
22:46which is the network between r1 and r2
22:50and 10.1.1.12 which
22:53is the network between r1 and r3
22:56alright so take note that
22:59the loopback network which is 10
23:021 1 or 10.10.1.0 is last 24 here
23:07so therefore the wild card mask would be
23:10a slash 24 so that's two five five that
23:12two five five the two five five the two
23:14five five
23:15minus two five five that two five five
23:17the two five five dot
23:19zero so that makes it zero that's zero
23:23that's zero dot two five pipe here
23:26right now this two here
23:29which is between r1 and r2
23:33right and of course also between r1 and
23:36r3 here
23:37these are both last 30 okay
23:41and that means that would be two five
23:44five all right so let me just write it
23:47here
23:48two five five okay so here with my
23:54um handwriting there two five five
23:57okay so i have a hard time using the
23:59mouse
24:00that slash 30 so 5 2
24:05okay so that means when we subtract it
24:08from 255
24:10okay that 255
24:15that 255
24:18okay that's two five five this will gl
24:22two of course you've got zero
24:25that's zero that's zero dot
24:28three so which are the wildcard masks
24:32here
24:34okay so take note that some ios versions
24:37allow the subnet mask to be entered
24:40instead of the wildcard mask
24:42so the ios then converts the subnet mask
24:45to the wildcard mask format all right
24:51okay so as an alternative
24:55okay so the second example shows
24:59how ospf version 2 can be enabled by
25:01specifying the exact
25:03interface ipb4 address using a quad
25:060 wildcard mask okay so
25:10entering network 10115
25:14right so you've got here
25:180.0.0.0 area 0 on r1
25:20which tells the router to enable
25:23interface
25:24gigabit ethernet 0 0 0
25:28for the routing process so as a result
25:31the ospf version 2 process will
25:33advertise the network
25:35that is on this interface 10
25:381 1 4 last 30. all right
25:43now the advantage of specifying the
25:46interface is that the wildcard mask
25:48calculation is not necessary
25:50so notice that in all cases
25:53the area argument specifies area zero
25:57so if you will observe here okay you've
26:00got one zero there
26:01so that means it is um
26:05more specific specifying the exact
26:07interface ipv4 address
26:10okay
26:11[Music]
26:14all right so next would be configure
26:17ospf
26:18using the ipo spf command okay
26:22now you can also configure ospf directly
26:25on the interface instead of using the
26:27network command
26:28so to configure ospf directly on the
26:31interface
26:32we use the ipo spf interface
26:36configuration mode command okay
26:39so the syntax is given here all right
26:44so router okay configure so ipo spf
26:47process id area and then you've got an
26:50area id
26:51now for r1 remove the network commands
26:54by using the no
26:55form of the network commands something
26:58like no network
26:5910 10 10 or 10 10 1 1
27:02okay zero zero zero zero area zero no
27:05network
27:06then one one five and then no network
27:08then one one fourteen
27:11okay and then go to each interface and
27:14configure ipo spf command
27:17as shown here so ipo spf 10
27:21area 0 okay so that is for interface
27:24gigabit ethernet 000
27:27interface gigabit 001 so
27:31in there you configured ipo spf 10 area
27:340
27:34but then most of the time we are using
27:37the network command
27:38all right so but then it's up to you you
27:40can use this um
27:42as an alternative of doing configuration
27:45okay
27:46for loopback 0 so ipo spf 10 area
27:49zero so it has the same effect
27:52right
27:57okay next would be let's talk about
28:00passive interface
28:02okay so by default ospf messages are
28:05forwarded out
28:07all ospf enabled interfaces so however
28:11these messages really only need to be
28:14sent out interfaces
28:16that are connecting to other ospf
28:18enabled routers
28:21now refer to the topology in the figure
28:23presented earlier
28:24ospf version 2 messages are forwarded
28:27out
28:28three loopback interfaces even though no
28:31ospf version to neighbor exists on this
28:35simulated lens so in a production
28:38network
28:39this loopbox would be physical
28:41interfaces to networks
28:43with users and traffic okay sending out
28:47unneeded messages on the lan affects the
28:50network in two ways as
28:52follows okay so first you've got
28:56an efficient right bandwidth
28:59so available bandwidth is consumed
29:01transporting unnecessary messages
29:05next would be inefficient use of
29:07resources
29:11okay so where's my pointer right so this
29:14is the second one
29:15inefficient use of resources
29:19so all devices on the lan must process
29:22and eventually discard the message
29:24so next would be increased security or
29:28risk
29:29so without additional ospf security
29:31configurations
29:33okay so ospf messages can be intercepted
29:36with packet snipping software so routing
29:39updates
29:40can be modified and sent back to the
29:42router corrupting the routing table
29:45with false metric that misdirect traffic
29:52okay
29:57all right so how do we configure
30:00a passive interface so we use the
30:03passive interface
30:05okay router configuration mode command
30:07to prevent
30:08transmission of routering messages
30:10through a router interface
30:12so but still allow that network to be
30:15advertised
30:16to the other routers so the
30:18configuration example identifies
30:20the r1 loopback okay
30:24the r1 loopback zero as
30:27passive okay so
30:30in here so router router ospf 10
30:34passive interface loopback zero so we
30:37are going to place
30:38loopback zero to a passive interface and
30:41therefore
30:42it will not receive any updates that is
30:45intended only
30:46for devices that is configured with ospf
30:50okay so usually okay so this passive
30:54interface command
30:55is being used if you are connecting a
30:57switch
30:58or a computer connected to that port
31:02but basically if you are connecting
31:05router okay so to another router we do
31:08not
31:09execute passive interface on that
31:11interface
31:12because it will not forward or it will
31:14not ascend or receive
31:17updates okay so for ospf
31:20all right now after this you could use
31:23the command show ip protocols
31:26okay so this is used to verify that the
31:29loopback zero interface is listed
31:32listed as passive here so below here
31:35so take note that passive interfaces
31:38they're listed loopback zero
31:44right
31:48okay so ospf point-to-point networks
31:51so by default cisco routers elect a dr
31:55and bdr on ethernet interfaces
31:58so even if there is only one other
32:01device on the link
32:03so you can verify this with a show ipo
32:05spf interface command
32:07so as shown here in the example for g00
32:11of r1 okay so as you can see here
32:15so show ipo spf interface g00
32:180 so network type is broadcast so that
32:22means
32:23it is on the multi-access
32:26network okay or an internet interface
32:31right so also you can see here the
32:34designated router id
32:36is 2.2.2 okay and the backup designated
32:39router id
32:40on that network would be 1.1.1
32:48all right so r1
32:51is the bdr and r2 is the tr
32:55okay so that is uh based on the output
32:57that we have earlier
32:59now the drbdr election process is
33:02unnecessary
33:04as there can only be two routers on the
33:06point-to-point network between
33:08r1 and r2 so notice in the output
33:13that the router has designated the
33:15network type as
33:16broadcast okay
33:20so to change this to a point-to-point
33:22network
33:24we use the interface configuration
33:25command ipo spf network
33:28point to point on all interfaces where
33:31you want to disable the drbdr election
33:33process
33:35right so the example below or in here
33:39shows this configuration for r1 so the
33:42ospf neighbor
33:44adjacency status will go down for a few
33:47milliseconds
33:49all right so as you can see here so ipo
33:53spf interface gigabit ethernet zero zero
33:56zero
33:57right so
34:00after some time okay after a few
34:02milliseconds notice that the gigabit
34:04ethernet zero zero zero interface
34:06now lists the network as type
34:09point to point and that there is no dr
34:13or bdr on the link okay
34:17so let me reiterate that dr and bddr is
34:19applicable only
34:21when you connect your router the switch
34:24right so we're in multiple routers are
34:26connected to it
34:32okay so loopbacks and point-to-point
34:34networks
34:35so we use loopbacks to provide
34:37additional interfaces for a variety of
34:40purposes
34:41in this case we are using loopbacks to
34:43simulate more networks
34:46than the equipment can support so by
34:48default
34:49loopback interfaces are advertised as
34:52last 32 host routes
34:55okay slash 32 host routes
34:59now for example r1 would advertise
35:0310 that 10 that one that zero class 24
35:06network as 10 that 10
35:10that's one that's one slot 32
35:13both to r2 and r3
35:17okay now to simulate
35:20a real lan the loopback zero interface
35:23is configured as
35:25point to point network so that r1 will
35:27advertise
35:28the full 10 10 1 0 network to r2
35:32and r3 right
35:35so if you can see here so interface
35:38debug 0
35:39ipo spf network point to point
35:44okay now r2 receives
35:47the more accurate simulated network
35:50address of 10
35:5110 1 0 24
35:56right so
36:00so i put out here so include 10 10 1
36:04so i'll have here 10 10 1 0 24
36:08is in there
36:13all right so next let's go to the next
36:16section
36:17multi-access ospf networks
36:20okay
36:25all right so on this section
36:28let's talk about the uspf network types
36:32so another type of network that uses
36:34ospf
36:35is the multi-access ospf network so
36:38multi-access ospf
36:40network are unique in that one router
36:43controls the distribution of lsas
36:46so the router that is elected for this
36:49role
36:50should be determined by the network
36:51administrator
36:53through proper configuration so
36:56ospf may include additional processes
36:59depending on the type of network
37:01so the previous topology used
37:03point-to-point links
37:05between the routers so however
37:08routers can be connected to the same
37:10switch to form a multi-access
37:13network so as shown here in the figure
37:16so we have connected
37:17four routers to a single switch so
37:21ethernet lands are the most common
37:23example of broadcast
37:25multi-access network so in a broadcast
37:28multi-access network or broadcast
37:29networks
37:31all devices on the network see all
37:33broadcast and multicast
37:35frame right
37:42okay so next would be the ospf
37:46designated router
37:48so recall that in multi-access network
37:52ospf elects a dr and bdr as a solution
37:56to manage the number of adjacencies and
37:58flooding of
37:59link state advertisements or lsas
38:02so the dr is responsible for collecting
38:05and distributing lsas
38:07sent and received so the dr uses the
38:10multicast ipv4 address
38:12as mentioned in the previous um
38:16video lecture that would be 224.0.0.5
38:20which is meant for all the ospf routers
38:24okay so a bdr is also elected
38:28in case that the dr fails now the bdr
38:32listens
38:33passively and maintains a relationship
38:35with all the routers
38:37so if the dr stops producing hello
38:40packets
38:41the dr promotes itself and assumes the
38:43role
38:44of the designated router or the dr
38:48now all other routers become a drawer
38:52so a router that is neither the dr
38:55nor the bdr so drawers use
38:59multi-access address 22406
39:03so all designated routers to send ospf
39:07packets to the dr and vdr
39:12so take note only the dr and bdr
39:16lesion four two two four zero
39:19zero six
39:26all right so what is the role of the dr
39:29or designated router
39:31so in the figure here r1 r5
39:35r4 are rotors
39:38right and the bdr process the lsa
39:42sent by r1 using multicast ipb4 address
39:4822406.
39:50now the drdin sends out the lsa
39:54okay to all the ospf routers using the
39:57multicast
39:58ipv4 address two two four zero zero five
40:04right so the dr is responsible
40:07for sending all the lsas to all the
40:10routers here
40:12okay so in that sense it eliminated
40:15the possibility of a flooded network
40:21okay so ospf
40:24multi-access reference topology so
40:28let's use this in a multi-access
40:30topology shown in the figure
40:32okay so there are three routers
40:34interconnected over a common internet
40:36multi-access network 192
40:40168 1.0 okay so that
40:43is slash 24 right
40:47now each router is configured with the
40:49indicated ipv4 address
40:51on the gigabit ethernet zero zero zero
40:53interface
40:55because the routers are connected over a
40:57common multi-access network
40:59ospf has automatically elected a dr
41:03and a bdr now in this example
41:07r3 has been elected as the dr
41:11why because its router id
41:14is three the three the three the three
41:17okay
41:18so the highest
41:21uh router id okay so in this case
41:25so 3.3.3.3 which is the highest in this
41:28network
41:29right so it will be chosen as the dr
41:33okay so r2 is the bdr
41:36because it has the second highest router
41:39id
41:40in the network which is 2.2.2.2
41:45right and therefore r1 here
41:48is a drawer
41:51right
41:54okay so how do we verify ospf
41:58router rules so to verify the rules of
42:01the ospf version 2 router
42:04we use the command show ipospf
42:07interface right
42:12now for instance we have here
42:15our consideration r1 is the drauder
42:19right so from the previous slide r1 was
42:22a droughter so the output generated by
42:25r1
42:26confirms that the following
42:29first r1 is not the dr
42:33or bdr but it is
42:37a drawer with a default priority of
42:40one right so take note
42:43state daughter priority one
42:48okay so next would be
42:51the dr is r3
42:54okay so take a look at this the
42:56designated router
42:58is r3 having a router id of
43:023.3.3.3 and that is connected via
43:05interface address 192.168.1.3
43:09so while the bdr is r2
43:13okay so with router id 2.2.2.2
43:16typey address 192.168. 1.2
43:20okay next r1 has two adjacencies
43:24one with a bdr and one with the dr
43:28okay so it's adjacencies take a look at
43:30this adjacent with neighbor to the two
43:32to the two which is the bdr and it is
43:35also adjacent with
43:373.3.3.3 which is a designated router
43:41all right so that's how to verify ospf
43:45router rules
43:48okay so let's check
43:51the r2 okay or the router 2 here
43:55so show ipo spf interface gigabit
43:57ethernet 0
43:580 0 here okay now the state here
44:02is the bdr and the priority is one so
44:05designated router is 3.3.3 that is
44:09connected to 192.168.1.3 here
44:12okay so while r2
44:15with router id 2.2.2.2 at ip address
44:20192.168.1.2
44:22the bdr okay so
44:25take note that on this line here r2 has
44:29two adjacencies
44:30one with the neighbor okay with router
44:33id
44:341.1.1.1 which is r1
44:37and the other with the dr which is
44:413.3.3.3 okay so again
44:44to verify the ospf router role we use
44:48the command
44:48show ipo spf interface and then you
44:51could type in the
44:53specific interface there
44:56okay now let us evaluate
44:59the router 3 okay so the output
45:02generated by r3 confirms that
45:05r3 is the dr with a default priority of
45:08one
45:08so as you can see here so state dr
45:11priority is one
45:13okay so designated router is 3.3.3.3
45:17connected at 192.168.1.3
45:20well the bdr is r2 with router id
45:23to the 2.2.2 at ipv4 address 192.168.1.2
45:29okay so r3 has two adjacencies
45:33one with neighbor with router id 1.1.1.1
45:38which is r1 and the other with
45:41the bdr okay so which is
45:462.2.2.2
45:48right so again the command to verify the
45:50ospf
45:51router rule is show ipo spf
45:55interface command
45:58all right next how do we verify
46:02dr and vdr adjacencies so to verify the
46:06osp of version to adjacencies
46:08we use the command show ip ospf neighbor
46:11command
46:12okay so as shown here right show ipos pf
46:16neighbor command
46:20okay so the state of neighbors in a
46:23multi-access networks can be as
46:25follows it could be a full and then
46:27rotor
46:28what does it mean so this is a dr
46:32or vdr okay
46:35so when you have seen on your router
46:37that the status or the adjacencies would
46:39be full brother
46:41this is a dro or video router that is
46:44fully adjacent
46:45with a non-dr or vdr
46:48router these two neighbors can exchange
46:52hello packets
46:53updates queries replies and
46:56acknowledgements
46:58okay so the next one would be
47:01full dr so the router is actually
47:05adjacent
47:06with the indicated dr neighbor
47:09so these two neighbors can exchange
47:11hello packets
47:12updates queries replies and
47:16acknowledgement also the next one is
47:19full bdr so the router is fully adjacent
47:23with an
47:24indicated bdr neighbor
47:27okay so these two routers or neighbors
47:31can exchange hello packets updates
47:33queries replies and acknowledgement
47:36all right so next would be
47:40a two-way daughter so the non-dr
47:44or bdr router has a neighbor
47:46relationship with another non-dr or bdr
47:49router
47:50so these two neighbors can exchange
47:52hello packets
47:55okay now the normal state of an ospf
47:58router is
47:59usually full if a router is
48:02stuck in another state it is an
48:05indication that there are problems
48:08in forming adjacencies so the only
48:10exception
48:12to this is the two-way state which is
48:14normal in a multi-access broadcast
48:16network
48:17for examples so drawers will form a
48:21two-way
48:21neighbor adjacency with any daughters
48:24that join the network so when this
48:28happens
48:29the neighbor state displays a two-way
48:32rather okay
48:41all right so next would be
48:44r1 adjacencies so the output generated
48:48by r1 confirms
48:49that okay r1 has adjacencies with the
48:53following routers
48:54okay so that would be
48:58r2 with router id 2.2.2.2
49:01this is in full state and the role of r2
49:04is
49:05bdr all right next would be
49:08with r3 that would be with router id
49:113.3.3.3
49:13okay so this is in full state
49:16and the role of r3 is dr
49:20okay now let us evaluate also the
49:23adjacencies on r2
49:25okay so show ipo spf neighbor as you can
49:27see here
49:28r1 with router id 1.1.1.1
49:32okay is in full state
49:36okay and r1 is neither dr
49:39or a nor vdr so take note that r1 is a
49:42dotter right
49:44okay so next r3
49:47with router id 3.3.3.3 is in full state
49:51okay and the role of r3 is dr
49:57all right now let us evaluate also
50:00r3 adjacency so show ipo sp of neighbor
50:02here
50:04okay now the output generated by r3
50:07confirms that r3 has adjacencies with
50:10the following routers
50:12so 1.1.1.1 that's r1 okay r1 router id
50:16is in full state
50:18okay and r1 is neither
50:22the dr nor the bdr r1 is a daughter
50:27and then r2 with router id 2.2 to the 2
50:30is in full state
50:31and the role of r2 sbdr
50:35all right
50:39okay so let's talk about the dr bddr
50:42election process
50:44so how do the dr and bdr get elected
50:48okay so the ospf dr
50:51and bdr election decision is based on
50:54the following criteria in sequential
50:56order
50:57right so first the routers in the
51:00network
51:01elect the router with the highest
51:03interface priority
51:05as the dr so the router with the second
51:08highest interface priority
51:10is elected as a bdr the priority can be
51:13configured
51:14to be any number between 0 to 255
51:18so if the interface priority is set to
51:20zero
51:22that interface cannot be elected as dr
51:25nor bdr so the default priority of the
51:29multi-access broadcast interface is
51:31one so therefore unless otherwise
51:35configured
51:36all routers have an equal priority value
51:39and must rely on another type breaking
51:41method during the dr
51:43and vdr election okay
51:47now the second one would be if the
51:50interface
51:52okay priorities are equal then the
51:55router with the highest router id
51:57is elected as the dr
52:00now the router with the second highest
52:02router id is the bdr
52:04recall that the router id is determined
52:06in one of the following three ways
52:09right just remember that so the router
52:11id can be manually configured
52:13okay so if no router id are configured
52:18the router id is determined by the
52:20highest loopback ipv4 address
52:23but then again if there is no loopback
52:25interfaces
52:26configured the router id is determined
52:29by the highest active
52:30ipb4 addresses
52:34all right
52:38okay so let's have the default
52:41drbddr election process now
52:44in the figure here all ethernet router
52:47interfaces
52:48have a default priority of one okay
52:52so as a result based on the selection
52:54criteria listed above
52:56the ospf router id is used to elect the
52:59dr
53:00and vdr so r3 here
53:04with the highest router id becomes the
53:06dr so take note that the router id here
53:08is 3.3.3.3 okay
53:12and r2 where the second highest
53:15router id becomes a pdr
53:19now the dr and bdr election process
53:21takes place as soon as the first router
53:24with an ospf enabled interface is active
53:27on the multi-access network
53:30so this can happen when the
53:32pre-configured ospf routers are powered
53:34on
53:35or when the ospf is activated on the
53:38interface
53:39the election process only takes a few
53:42seconds
53:43so if all of the routers on the
53:46multi-access network have not
53:48finished booting it is possible that a
53:51router with a lower
53:52router id becomes the dr
53:56okay now ospf dr
53:59and bdr elections are not preemptive
54:03if a new router with a higher priority
54:06or
54:07higher router id is added to the network
54:10after the dr and bdr election the newly
54:13added router does not take
54:15over the dr or bdr role okay so this is
54:18because
54:19those rules have already been assigned
54:22now the addition of the new router
54:25does not initiate a new election process
54:29all right
54:32okay so dr failure
54:36and recovery so after the dr is elected
54:40it remains the dr until one of the
54:43following events occurs
54:45right so first dr fails
54:49okay the second would be
54:52the ospf process on the dr fails or is
54:55stopped and then third
54:59the multi-access interface on the dr
55:01fails or is shutted down
55:03so if the dr fails the pdr is
55:06automatically promoted
55:08to a dr roll this is the case
55:11even if another router with a higher
55:14priority or router id
55:15is added to the network after the
55:17initial
55:19drpdr election however
55:22after a bdr is promoted to a dr
55:25a new bdr election occurs and that rotor
55:29with the highest priority or
55:31router id is elected as the new bdr
55:35okay so that's how it goes
55:39next so in this example here okay
55:42on this illustration okay so
55:46r3 fails remember that r3 is our dr
55:49right so in this scenario the current dr
55:52which is
55:52r3 fails so therefore
55:55the pre-selected bdr which is r2
55:59assumes the role of the dr subsequently
56:03okay an election is held to choose a new
56:06bdr
56:07because r1 is the only drawer it is
56:10elected as the bdr
56:13all right
56:16okay so what will happen if r3
56:20rejoins the network now in this scenario
56:24r3 has rejoined the network after
56:27several minutes of being unavailable
56:30okay so because the dr and ddr already
56:33exists
56:34r3 does not take over either role
56:37so instead it becomes a throttle
56:41all right
56:45okay so next what would be
56:48or what would happen if r4 joins the
56:51network
56:52now in this scenario okay a new router
56:55r4
56:56with a higher router id is added to the
56:58network
56:59so r2 which is the dr
57:03and r1 which is the bdr
57:07retain the dr and the bdr roles so r4
57:11automatically becomes a daughter along
57:14with
57:14r3 here right
57:19okay so what if are two fields
57:24okay in this scenario r2 has failed
57:28the bdr which is r1 automatically
57:31becomes
57:32the dr and an election process selects
57:36r4 as the bdr
57:39because it has the higher router
57:42id all right
57:47okay so how about the ipo spf
57:51priority command now if the interface
57:54priorities are equal on all
57:56routers the router with the highest
57:58router id is selected
58:00the dr now it is possible to configure
58:03the router id
58:04to manipulate the drbdr election okay so
58:08however
58:09this process only works if there is
58:13a stringent plan for setting the router
58:16id
58:17on all the routers so configuring the
58:20router id can help control this however
58:23in a large networks this can be
58:25cumbersome
58:27okay now instead of relying on the
58:30router id
58:31it is better to control the election by
58:33setting the interface priorities
58:35so this is
58:39or this also allows a router to be the
58:42dr
58:43in one network and a drawer in another
58:45network that's possible
58:47okay now to set the priority
58:51of an interface we use the command ipo
58:53spf
58:54priority value where value is from zero
58:57to two five five
58:59okay so a value of zero does not become
59:01a d or
59:02a pdr a value of 1 to 255 on the
59:05interface
59:06makes it more likely that the router
59:08becomes dr or
59:09the bdr
59:16okay
59:18all right so let us configure the ospf
59:21priority
59:22so the following example shows how to
59:24clear the ospf
59:26process on r1 so clear ipo spf process
59:30okay command that must be entered on r2
59:33and r3 also
59:34which is not shown on this diagram here
59:37notice the ospf state information
59:39that is generated here okay
59:42so see this so there are some sort of
59:45notifications here
59:46adjacencies all right process 10
59:50right so from full to down okay
59:53interface down or detected
59:58all right now how do we configure ospf
1:00:01priority so in the topology
1:00:04the ipo sp a priority command will be
1:00:07used to change the dr
1:00:08and bdr as follows okay so r1 should be
1:00:12dr and will be configured with a
1:00:14priority of two five five so take note
1:00:16that we can use
1:00:17numbers zero two two five five but then
1:00:20zero
1:00:22setting it to zero so your router will
1:00:24not participate in the election process
1:00:26right now setting it to the highest will
1:00:28ensure
1:00:29that r1 will become the dr
1:00:33right so r2 should be the bdr
1:00:36and we'll be left with a default
1:00:38priority with one and maybe
1:00:40on r3 okay r3 should never be a d or bdr
1:00:44and will be configured with a priority
1:00:46of zero
1:00:48okay now change the r1 g00 interface
1:00:51priority from one to two five five
1:00:54okay and change the r3g00 interface
1:00:57priority from one
1:00:59to zero all right
1:01:07okay so let's go to the next section
1:01:11so modifying a single area ospf version
1:01:14two
1:01:18now in here on this section let's talk
1:01:20about
1:01:22uh the cisco ospf cost metric
1:01:26so recall that a routing protocol uses a
1:01:29metric to determine the best path
1:01:31okay of a packet across the network so a
1:01:34metric gives indication
1:01:36of the overhead that is required to send
1:01:38packets across
1:01:39certain interface so ospf uses cost
1:01:43asymmetric
1:01:45a lower cost indicates a better pass
1:01:47than a higher cost
1:01:50the cisc cost of an interface is
1:01:52inversely proportional to the bandwidth
1:01:55of the interface
1:01:56so therefore a higher bandwidth
1:01:58indicates a lower cost
1:02:00so the formula used to calculate the
1:02:02ospf cost
1:02:04would be cost reference bandwidth
1:02:08divided by the interface bandwidth now
1:02:11the default reference bandwidth is 10
1:02:13raised to 8
1:02:15okay therefore the formula is cost
1:02:19okay so which is 10 raised to 8 bps
1:02:23divided by the interface bandwidth in
1:02:25bps also
1:02:27now refer to the table for a breakdown
1:02:30of cost calculation
1:02:31because the ospf cost value must be an
1:02:34integer
1:02:35so fast internet gigabit internet and 10
1:02:38gig
1:02:39ethernet or interfaces share the same
1:02:42cost
1:02:43so to correct the situation you can
1:02:46adjust the reference bandwidth
1:02:48with the auto cost reference bandwidth
1:02:50command
1:02:51on each of the ospf router so manually
1:02:54set the ospf cost value
1:02:56with an ipo spf cost command on
1:02:59necessary interfaces
1:03:03all right now this is the table that we
1:03:05are pertaining to in the previous slide
1:03:07okay so basically you just have to refer
1:03:10to this table
1:03:11if you are using 10 gbps or 10g ethernet
1:03:15the cost is one right
1:03:18so also gigabit internet
1:03:22pass internet and ethernet okay
1:03:25same cost due to reference bandwidth
1:03:28okay so which are all
1:03:29one all right so you don't have to
1:03:33compute just refer to this table here
1:03:37okay so adjusting the reference
1:03:39bandwidth
1:03:40so the cost value must be an integer
1:03:44okay if something less than an integer
1:03:47is calculated
1:03:48ospf rounds up to the nearest integer so
1:03:51therefore
1:03:52the ospf cost assigned to the gigabit
1:03:55ethernet interface with a default
1:03:57reference bandwidth
1:03:58of 10 raised to 8 bps would equal to
1:04:021 because the nearest integer for 0.1 is
1:04:050
1:04:06instead of 1. right
1:04:09so that would be cost 10 raised to 8
1:04:13okay divided by the
1:04:16bandwidth okay so that would be equals
1:04:18to 1.
1:04:19so for this reason all interfaces faster
1:04:22than fast internet
1:04:24will have the same cost value of 1 as a
1:04:27fast ethernet interface
1:04:29so to assist ospf in making the correct
1:04:32path determination
1:04:34the reference bandwidth must be changed
1:04:36to higher value
1:04:37to accommodate networks with links
1:04:39faster than
1:04:40100 mbps
1:04:44okay now changing the reference
1:04:47bandwidth does not actually affect the
1:04:49bandwidth capacity of the link
1:04:51so rather it simply affects the
1:04:53calculation used to determine the metric
1:04:57so to adjust the reference bandwidth we
1:04:59use the command
1:05:00auto cost reference bandwidth
1:05:03that is an mbps router configuration
1:05:06command
1:05:07all right so here's the syntax okay
1:05:12now this command must be configured on
1:05:15every router
1:05:16in the ospf domain notice that the value
1:05:19is expressed in
1:05:20mbps so therefore to adjust the cost
1:05:24for gigabit ethernet we use the command
1:05:27auto cost reference bandwidth right
1:05:301000 for 10 gigabit ethernet
1:05:35use the command auto cost reference
1:05:37bandwidth 10 000
1:05:40all right
1:05:44okay so whichever method is used it is
1:05:47important to apply the configuration
1:05:49to all routers in the ospf routing
1:05:51domain so the table
1:05:52shows right here the ospf cost
1:05:57if the reference bandwidth is adjusted
1:05:59to accommodate 10 giga ethernet or
1:06:01gigabit ethernet links
1:06:03so the reference bandwidth should be
1:06:04adjusted anytime
1:06:06there are links faster than past
1:06:09ethernet or 100 mbps okay
1:06:13so in here if you are using 10 10 gbps
1:06:15one
1:06:16okay same thing with giga internet
1:06:19okay so looking at this table stand
1:06:23past ethernet is 100 and gigabit
1:06:26internet
1:06:28or sorry eastern at 10 mbps okay or the
1:06:31internet alone
1:06:32is 1000
1:06:35all right
1:06:41okay so ospf accumulates
1:06:45cost so the cost of an ospf route is the
1:06:49accumulated value from one router
1:06:51to the destination network assuming the
1:06:54auto cost
1:06:55ospf bandwidth okay so 10 000 command
1:06:59has been configured on all the three
1:07:00routers
1:07:01now the cost of the links between each
1:07:04router is now
1:07:0510 right that cost
1:07:09all of those are 10. now the loopback
1:07:11interface
1:07:12have a default cost of one as shown in
1:07:15the figure
1:07:18all right
1:07:24okay so therefore we can calculate the
1:07:27cost
1:07:28for each router to reach each network so
1:07:30for example
1:07:32the total cost for r1 okay
1:07:35to reach 10 10 to 0
1:07:39which is this one here okay
1:07:42is 11 so how did we get 11 right
1:07:45so that would be 10 plus 1 that is 11.
1:07:50so this is because the link on r2 cost
1:07:52okay that's what i'm saying
1:07:53is 10 and the loopback default cost is
1:07:561. so 10 plus 1 that is
1:07:5811.
1:08:03all right so the routing table of r1
1:08:06here okay in the figure confirms that
1:08:08the metric to reach
1:08:10r to lan is at cost 11. so see this
1:08:13metric 11. so if you if you use the
1:08:17show i put out right that's 110 over 11.
1:08:20so this pertains to the cost
1:08:27okay so can we manually set ospf cost
1:08:30value
1:08:31yeah so ospf cost values can be
1:08:34manipulated to influence the route
1:08:36chosen by ospf
1:08:38now for example now in the current
1:08:41configuration
1:08:42r1 is load balancing to 10 118
1:08:47slash 30 right so
1:08:5010 1 1 8 slash 30
1:08:54now in here so how do we know that this
1:08:57is load balanced
1:08:59right so you have two possible paths to
1:09:01get into that network so it's either by
1:09:03a 10 113
1:09:05and 10 1 1 6. okay
1:09:08now it will send some traffic to r2 and
1:09:10some traffic to
1:09:11r3 okay so because we can see it
1:09:15on the routing table right so if we are
1:09:17r1 on r1
1:09:18so we could forward some traffic here
1:09:21and some traffic also in here
1:09:23to get to 10 1 1 8 which is
1:09:26the network between r2 and r3
1:09:34okay so the administrator may want
1:09:37traffic to go to r2 and use r3 as a
1:09:40backup problem
1:09:42that's what we did in static routing
1:09:44right so floating static
1:09:46route sort of okay in case the link
1:09:49r1 and r2 goes down okay
1:09:53so another reason to change the cost
1:09:55value is because
1:09:56other vendors may calculate ospf in a
1:10:00different manner
1:10:01so by manipulating the cost value the
1:10:04administrator can make sure
1:10:06the route costs shared between ospf
1:10:09multi-vendor routers
1:10:10are accurately reflected in the routing
1:10:12table
1:10:14now to change the cost of value reported
1:10:16by the local ospf router to another ospf
1:10:19routers
1:10:20we use the interface configuration
1:10:22command ipo spf
1:10:24host value okay
1:10:27this is to simulate gigabit ethernet
1:10:31speeds so in addition we will change the
1:10:34cost of the link
1:10:35between r2 okay
1:10:39and r3 to 30 so that this link
1:10:42is used as a backup link
1:10:45all right so in that case she's going to
1:10:47have this
1:10:48okay so interface g001 ipo spf cost
1:10:5330. and then interface loopback 0
1:10:57ipo spf cost 10.
1:11:01right okay
1:11:04now assuming ospf cost for r2
1:11:09okay and r3 have been configured to
1:11:12match the topology
1:11:13in in the figure or on this powerpoint
1:11:16here
1:11:16okay so the ospf browse for r1 would
1:11:20have the following cost values
1:11:22so notice that r1 is no longer load
1:11:25balancing
1:11:26to 10 118 so you only have
1:11:29one path here which is via 10116
1:11:33okay so in fact
1:11:37all routes going to r2 as desired by
1:11:41a network administrator okay so also
1:11:44note that
1:11:45although using the ipo spf cost command
1:11:48is the recommended method to manipulate
1:11:50the ospf cost values
1:11:52an administrator could also do this by
1:11:55using the interface configuration
1:11:57bandwidth kbps command however
1:12:01that would only work if all the routers
1:12:04are
1:12:04cisco routers okay
1:12:09next so test fill over
1:12:12to backup route so what happens if the
1:12:15link between r1 and r2 goes down
1:12:18so we can simulate that by shutting down
1:12:21the gigabit ethernet 000
1:12:25right and verifying that the routing
1:12:28table is updated to use r3 as the next
1:12:31top router
1:12:32so notice that r1 can now reach the
1:12:3510114
1:12:36slash 30 network through r3
1:12:39with a cost value of 50.
1:12:45all right so that's 50 there
1:12:52okay so next modifying the single area
1:12:56spf version 2 hello packets
1:12:58interval so as john in the figure
1:13:01ospf version 2 hello packets are
1:13:04transmitted
1:13:05to multi-cast address 22405
1:13:09all spf routers every 10 seconds
1:13:12okay now this is the default timer
1:13:15on a multi-access and point-to-point
1:13:17networks
1:13:18take note that hello packets are not
1:13:20sent on a simulated lan interfaces
1:13:22because
1:13:23those interfaces were set to passive by
1:13:26router configuration passive interface
1:13:28command earlier
1:13:30now the dead interval is the period
1:13:33that the router waits to receive hello
1:13:35packet before declaring that the network
1:13:38is down
1:13:39now if the dead interval expires
1:13:42before the routers receive the hello
1:13:45packet
1:13:46ospf removes that neighbor from the link
1:13:50state database or lsdb
1:13:52okay now the router floods the lsdb with
1:13:55information about the down neighbor
1:13:58out all ospf enabled interfaces
1:14:01so cisco uses a default of four times
1:14:05the interval or the hello interval so
1:14:08this is 40 seconds on a multi-axis
1:14:10and point-to-point networks right
1:14:14now on a non-broadcast multi-access or
1:14:17nvme networks
1:14:18the default hello interval is 30 seconds
1:14:22and the default dead interval is 120
1:14:25seconds
1:14:26so nbma networks are beyond the scope of
1:14:29this module
1:14:31right okay so how do we verify
1:14:36hello and dead intervals
1:14:40so the ospf hello entered intervals are
1:14:42configurable
1:14:44on a peer interface basis so the ospf
1:14:47interval must match
1:14:49or enable adjacency does not occur
1:14:52so to verify the currently configured
1:14:54ospf version to interface
1:14:55intervals we use the command show ipo
1:14:58spf
1:14:59interface and then the interface
1:15:02okay now the gigabit internet 0
1:15:060 0 here hello and that intervals are
1:15:09set at the default so if you will
1:15:11observe here
1:15:12it's 10 and 40. so the dead timer
1:15:15is four times the hello timer
1:15:18right
1:15:22now the show ipo spf neighbor command
1:15:25okay so we can use also this to see that
1:15:28that time
1:15:29counting down from 40 seconds as soon in
1:15:32the following example
1:15:33by default this value is repressed every
1:15:3610 seconds
1:15:38okay when r1 receives a hello from
1:15:41the neighbor
1:15:47okay so it may be desirable to change
1:15:51the ospf timers
1:15:52so that routers detect network failures
1:15:55in less time
1:15:56now doing this increases traffic but
1:15:59sometimes
1:16:00the need for quick convergence is more
1:16:02important
1:16:03than extra traffic it creates okay
1:16:06so take note that the hello and that
1:16:08intervals are based on the best
1:16:10practices
1:16:11and should only be altered in a rare
1:16:13situation
1:16:15okay so ospf version 2 hello and that
1:16:18intervals
1:16:19can be modified manually using the
1:16:22following interface configuration mode
1:16:23command so you could use
1:16:25no ipo spf hello interval and no ipo spf
1:16:30jet interval commands to reset intervals
1:16:34to their default which are 10 and 40.
1:16:40okay now in the example
1:16:43the hello interval of the link between
1:16:45r1 and r2
1:16:47is changed to five seconds
1:16:50okay up there
1:16:54so immediately after changing the hello
1:16:56interval the cisco ios
1:16:58automatically modifies the dead interval
1:17:00to four times the hello interval
1:17:02however you can document a new the
1:17:06interval in the configuration by
1:17:07manually setting it to 20 seconds as
1:17:09shown
1:17:10right so as displayed in the highlighted
1:17:13ospf version to adjacency here
1:17:16okay when the dead timer on r1 expires
1:17:19r1 and r2 lose adjacencies
1:17:23so the reason is because r1 and r2 must
1:17:26be configured
1:17:27with the same hello interval so better
1:17:30okay so not configure this or not alter
1:17:33the default settings
1:17:35now we use the command show ipo spf
1:17:37neighbor command on r1
1:17:39to verify the neighbor adjacencies so
1:17:42notice that
1:17:43only neighbor listed is the
1:17:463.3.3 here okay
1:17:51see that r3 router and that r1 is no
1:17:54longer adjacent
1:17:56with 2.2.2.2 r2 neighbor
1:17:59so beware of changing this timers
1:18:03so ensure if you have changed that on
1:18:05one end you have to do the same on the
1:18:07other end
1:18:10okay so to restore adjacencies
1:18:14between r1 and r2 the r2 gigabit
1:18:17ethernet 000 interface hello interval is
1:18:20set to five seconds
1:18:23okay so as soon in the following example
1:18:25here almost immediately the ios displays
1:18:28a message that adjacency has been
1:18:30established
1:18:31with a state of full
1:18:34right so verify the interface intervals
1:18:37using the show ip ospf interface command
1:18:43okay so notice that the hello time
1:18:47is 5 seconds and the dead timer
1:18:49automatically set to 20 seconds so
1:18:51instead of the default
1:18:5340 seconds right
1:19:00all right so next section let's talk
1:19:02about the default route propagation
1:19:08okay so default route propagation
1:19:11shall propagate a default static route
1:19:14in ospf version 2.
1:19:16so your network users will need to send
1:19:20packets out of your network
1:19:22to a non-ospf network such as the
1:19:24internet here
1:19:26okay now this is where you will need to
1:19:29have a default static route
1:19:31that can use or that they can use
1:19:34now in the topology okay so r2
1:19:37is connected to the internet and should
1:19:40propagate a default route
1:19:43to r1 and r3
1:19:46now the router connected to the internet
1:19:48is sometimes called the edge router
1:19:51or the gateway router so however
1:19:54in ospf terminology the router located
1:19:58between the ospf routing domain
1:20:00and the nano spf network is called
1:20:02autonomous system boundary router
1:20:05or the asbr okay
1:20:09asbr stands for autonomous
1:20:12system boundary router
1:20:16okay now how do we propagate a default
1:20:18route
1:20:20so to propagate the default route the
1:20:22edge router
1:20:23which is r2 on the previous uh topology
1:20:26presented
1:20:27must be configured with the following
1:20:29okay
1:20:30so we could have a default static route
1:20:33using the ipad out
1:20:350.0.0.0 0.0.0.0 we have the option to
1:20:39use
1:20:40next hub ip address or the exit
1:20:41enterprise command
1:20:43like what we did on the static route or
1:20:46the static routing
1:20:47okay now the default information
1:20:49originate
1:20:50router configuration command so this
1:20:53instructs r2
1:20:55to be the source of the default route
1:20:57information
1:20:58and propagate the default starter route
1:21:00in the ospf updates
1:21:03now in the following example so r2 is
1:21:07configured
1:21:09with a loopback to simulate the
1:21:11connection to the internet
1:21:27in the routing domain okay so the
1:21:29command is
1:21:31okay so default information originate
1:21:35now when configuring a static route best
1:21:38practice is to use the nextup ip address
1:21:40however
1:21:41when simulating a connection to the
1:21:43internet there is no next top ip address
1:21:45so therefore
1:21:47we use the exit interface instead
1:21:50all right
1:21:53okay so how do we verify the propagated
1:21:56default route so you can verify
1:22:00the default route settings on r2 using
1:22:03the
1:22:04show ip route okay so notice that
1:22:07the route source on r1 and r3 is
1:22:11oe2 right you'll have this oe2
1:22:15okay so signifying that it was learned
1:22:18using the osp of version 2. now the
1:22:21asterisk identifies this is a good
1:22:24candidate for the default route
1:22:27the e2 designation identifies that it is
1:22:30an external
1:22:32route okay the meaning of e1 and e2 is
1:22:35beyond the scope of this module
1:22:38right
1:22:42okay so let's go to the next section so
1:22:45verify single area
1:22:46ospf version 2.
1:22:52okay so verify ospf neighbors so if you
1:22:55have
1:22:55configured a single area osp of version
1:22:582
1:22:58you will need to verify your
1:23:00configurations
1:23:01okay this topic details the many
1:23:04commands
1:23:05that you can use to verify your spf so
1:23:08as you know
1:23:09the following two commands are
1:23:11particularly useful
1:23:12for verifying routing so these are of
1:23:14course the show i've interface brief
1:23:17okay this verifies that the desired
1:23:20interfaces are active
1:23:21with the correct ip addressing so the
1:23:24next one would be show ip route
1:23:26this verifies that the routing table
1:23:27contains all the expected routes
1:23:30now additional commands for determining
1:23:33that ospf is operating as expected
1:23:35include the following so you can use
1:23:37show ipo spf neighbor
1:23:39show ip protocol so ipo spf right or the
1:23:43show ipo spf interface command
1:23:46okay
1:23:52okay so how do we verify your spf
1:23:54neighbors so we use the command show ip
1:23:56usb of neighbor command to verify
1:23:58that the router has formed an adjacency
1:24:00with its neighboring routers
1:24:02now if the router id of the neighboring
1:24:05router is not displayed
1:24:06or it does not show as being in the
1:24:09state of full
1:24:10the two routers have not formed an ospf
1:24:13version to adjacencies
1:24:15okay now if two routers do not establish
1:24:18adjacency
1:24:19link state information is not exchanged
1:24:22so incomplete lsdbs can cause inaccurate
1:24:26spf trees and routing tables so routes
1:24:30to destination networks may not exist or
1:24:34may not be the most optimum path so take
1:24:37note that a non-dr
1:24:39or bdr router that has a neighbor
1:24:41relationship with
1:24:42another or video router will display a
1:24:45two-way adjacency instead of four
1:24:49okay now for each neighbor
1:24:52so this command displays the following
1:24:54so you've got the neighbor id
1:24:56okay so this is the router id
1:25:00of the neighboring router you also have
1:25:02pry
1:25:03okay so this is the ospf version to
1:25:05priority on the interface
1:25:07so this value is assigned in the dr and
1:25:09vdr election
1:25:11right so next would be state
1:25:14this is the osp of version to state of
1:25:17the interface so full state means
1:25:20that the router and its neighbor have
1:25:21identical osp operation to lsdbs
1:25:25now on a multi-axis network such as the
1:25:27ethernet
1:25:28two routers that are adjacent may have
1:25:31their states
1:25:32displayed as two-way the dash
1:25:35indicates that no dr or bdr is required
1:25:38because of the network type right
1:25:42so the next one is a dead timer okay
1:25:45so what's a dead timer this is the
1:25:48amount of time
1:25:49remaining that the router waits to
1:25:52receive an ospf version to help
1:25:54packet from the neighbor okay before
1:25:57declaring the neighbor is down now this
1:26:00value is reset when the interface
1:26:02receives a hello packer
1:26:05okay so the next one would be address
1:26:07this
1:26:08is the ipv4 address of the interface of
1:26:11the neighbor
1:26:12to which this router is directly
1:26:13connected
1:26:15and the last one is interface this
1:26:18is the interface on which this router
1:26:20has formed adjacency
1:26:22with the network
1:26:26okay so two routers may not form an osp
1:26:30of version to adjacency
1:26:32if the following occurs so first the
1:26:35subnet mask do not match
1:26:37okay so causing the routers to be on a
1:26:40separate networks
1:26:41the ospf version 2 hello and jetted
1:26:44timers
1:26:45do not match the ospf version 2 network
1:26:49types do not match and there is amazing
1:26:53or incorrect ospf version 2
1:26:55network command
1:27:00okay now next would be verify ospf
1:27:04protocol settings so we are using the
1:27:07command show ib protocols command as
1:27:09quickly
1:27:09or as a quick way to verify vital ospf
1:27:12configuration information
1:27:14okay so this includes the ospf
1:27:18version to process id router id
1:27:21interfaces explicitly configured to
1:27:23advertise ospf routes
1:27:25the neighbors the router is receiving
1:27:27updates from
1:27:29and the default administrative distance
1:27:32which
1:27:32is 110 for ospf
1:27:36okay so the show ib protocols command is
1:27:39a quick way to verify vital ospf
1:27:41configuration information
1:27:43so this includes uh ospf
1:27:47version two process id router id
1:27:50interfaces explicitly configured to
1:27:52advertise ospf routes
1:27:54the neighbors the router is receiving
1:27:55updates from
1:27:57and the default administrative distance
1:27:59which is 110
1:28:00for ospf right
1:28:04so the default administrative distance
1:28:05for static is
1:28:12one
1:28:16okay so verify ospf process information
1:28:21so the show ipo spf command can also be
1:28:24used to examine the ospf version 2
1:28:26process id
1:28:27and router id so as shown in the
1:28:28following command output here
1:28:30okay show ipos pf
1:28:34okay so you can see there so routing
1:28:36process ospf then with router id
1:28:38uh one one one one so this command
1:28:41displays the ospf version to
1:28:43area information and the last time the
1:28:46spf algorithm was
1:28:48executed okay so you can see here spf
1:28:51algorithm
1:28:52executed four times
1:28:56all right so
1:28:59next the show ipo spf interface command
1:29:03provides a detailed list of
1:29:05every ospf version to enable interface
1:29:08okay so i specify an interface to
1:29:11display the settings
1:29:13of just the interface as shown in the
1:29:15following output here for gigabit
1:29:16ethernet
1:29:18000 okay
1:29:21now this command shows the process id
1:29:24the router id okay or the local router
1:29:27id
1:29:29the type of the network which is point
1:29:31to point here
1:29:32the cost okay next would be
1:29:37dr and bd are information on
1:29:39multi-access links
1:29:40which are not shown and adjacent
1:29:43neighbors
1:29:47okay now to get a quick summary
1:29:50of ospf version to enable interfaces
1:29:54okay so use the show ipo spf interface
1:29:56brief
1:29:58okay so as you see here
1:30:01okay so this command is useful for
1:30:03seeing the important information
1:30:05including the following
1:30:06so something like the interface or
1:30:08interfaces are participating in ospf
1:30:12networks that are being advertised ip
1:30:14address k
1:30:15mask cost of its link right
1:30:19so network state and number of
1:30:23neighbors on each link
1:30:29okay so we come to an end of this video
1:30:32lecture
1:30:33it's a very long discussion okay so
1:30:35thank you for watching and listening
1:30:37have a great day hope you learned
1:30:39something from this video lecture today
1:30:48[Music]
1:30:52you

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