Eigrp Learning Route from Neighbour Router

[mahesh18]

Hi Everyone,

I have 3 routers R1 R2 and R3 .

All are EIGRP neis on AS 123.

R1  config

router eigrp 123

redistribute connected

passive-interface default

no passive-interface FastEthernet1/0/1

no passive-interface FastEthernet1/0/3

distribute-list 9 out

no auto-summary

network 10.0.0.0 0.0.0.3

network 192.168.1.0

R2 Config

router eigrp 123

redistribute static

passive-interface default

no passive-interface FastEthernet2/0/1

no passive-interface FastEthernet2/0/11

no auto-summary

network 10.0.0.0 0.0.0.3

network 10.1.23.0 0.0.0.255

network 192.168.1.0

R3 config

!

router eigrp 123

passive-interface default

no passive-interface GigabitEthernet1/0/11

network 10.1.23.0 0.0.0.255

no auto-summary

R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D EX    172.16.1.0/24
           [170/158720] via 10.1.23.2, 06:27:47, GigabitEthernet1/0/11
D EX    172.16.3.0/27
           [170/158720] via 10.1.23.2, 06:27:47, GigabitEthernet1/0/11
     172.31.0.0/24 is subnetted, 1 subnets
C       172.31.253.0 is directly connected, Vlan253
     10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
C       10.1.1.2/32 is directly connected, Loopback2
C       10.1.1.3/32 is directly connected, Loopback3
C       10.1.1.0/32 is directly connected, Loopback0
D       10.0.0.0/30 [90/30720] via 10.1.23.2, 06:27:47, GigabitEthernet1/0/11
C       10.1.1.1/32 is directly connected, Loopback1
C       10.1.23.0/24 is directly connected, GigabitEthernet1/0/11
D    192.168.1.0/24 [90/30720] via 10.1.23.2, 06:27:49, GigabitEthernet1/0/11
R3#

My question is  in order for  R3 to learn route of 192.168.1.0 through EIGRP from R2  why we need to advertise  the route with  network command

network 192.168.1.0    on R2?

As all 3 routers are in same AS  123.

I know that Network command is used to advertise the routes.

Does it is necessary in EIGRP  to advertise the route to using neighbor command so that  Nei router can learn it?

Thanks

Mahesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

Yes, if you want to advertise a route to EIGRP, you need to advertise the route via the network command or "redistribute direct" command.  But if you use redistribute direct, then all interfaces will be redistributed.  So, it is a good idea to use the network command.

HTH

Reza

[kcnajaf]

HI Mahesh,

The network statement under EIGRP does not advertise any networks. What the network statement does is tell the router on which interfaces to run EIGRP.

It is difficult to answer your query regarding route advertisement with out seeing "show ip int brief" from your routers.

The "neighbor' command under eigrp send a unicast request to the neighbor as opposed to the multicast address 224.0.0.10. It is not neccessary to put neighbor command for EIGRP to learn route fromt he nei. The neighbot command comes handy when the specific link does not support multicast/brodcast traffic like in the case of frame-relay circuits.

Hope that helps.

Regards

Najaf

Please rate when applicable or helpful !!!

[InayathUlla Sharieff · Accepted solution]

Hi MAhesh,

When the network command is configured for an  EIGRP routing process, the router matches one or more local interfaces.  Thenetwork command matches only local interfaces that are configured with  addresses that are within the same subnet as the address that has been  configured with the network command.

http://www.cisco.com/en/US/docs/ios/iproute_eigrp/command/reference/ire_i1.html#wp1026909

If you have connectivity between each other switches, and all the 3 routers are running the same EIGRP AS, advertising the 192.X network on R1 will be enough as that would be propagated to all the routers.

Just simple EIGRP update mechanism.

Example:

I have the following setup:

R1----s0/0---------s0/0----R2---------s0/1----------------------s0/1----R3

|

l0-192.168.0.1;;;;         LO- 2.2.2.2;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;L0-3.3.3.3

Config:

R1#sh ip int br

Interface                  IP-Address      OK? Method Status                Protocol

Serial0/0                  172.168.0.1     YES manual up                    up     

Loopback2                  192.168.0.1     YES manual up                    up 

router eigrp 100

network 172.168.0.0

network 192.168.0.0

no auto-summary

R1#sh ip route

D       89.0.0.0 [90/2681856] via 172.168.0.2, 00:06:35, Serial0/0

     192.168.0.0/32 is subnetted, 1 subnets

-----------------------------------------------------------------------------------------------

R2 : Not advertising 192.x network but its getting learned through eigrp.

R2#sh ip int br

Interface                  IP-Address      OK? Method Status                Protocol

Serial0/0                  172.168.0.2     YES manual up                    up     

Serial0/1                  89.0.0.1        YES manual up                    up     

router eigrp 100

network 89.0.0.0

network 172.168.0.0

no auto-summary

R2#sh ip route  192.168.0.0

Routing entry for 192.168.0.0/32, 1 known subnets

  Redistributing via eigrp 100

D       192.168.0.1 [90/2297856] via 172.168.0.1, 00:05:52, Serial0/0

-----------------------------------------------------------------------------------------------

R3

R3#sh ip int br

Interface                  IP-Address      OK? Method Status                Protocol

Serial0/1                  89.0.0.2        YES manual up                    up

router eigrp 100

network 89.0.0.0

auto-summary

R3#sh ip route 192.168.0.0 

Routing entry for 192.168.0.0/32, 1 known subnet

  Redistributing via eigrp 100

D       192.168.0.1 [90/2809856] via 89.0.0.1, 00:07:57, Serial0/1 >>>>>>>>.. It got learned from R2 hence no need to advertise it on the R2.

-----------------------------------------------------------------------------------------------

NOTE: If in case you are using 192.168.x.x network on R2 serial/gig/fast interface which are connecting to these routers then yes you need to advertise it on R2.

2-

Regarding Neighbor command:

neighbor x.x.x.x interface#/#

This command is executed in router configuration mode to specify a static neighbor in EIGRP, commonly used in NBMA networks where multicast is not permitted. This command will disable the transmission or processing of received eigrp multicast traffic.

more info:http://www.freeccnaworkbook.com/workbooks/ccna/configuring-eigrp-static-neighbors

HTH

Regards

Inayath

[mahesh18]

Hi Inayath,

R1  and R2 are connected by Fasethernet interface.

R1

R1#sh ip int brief
Interface              IP-Address      OK? Method Status                Protocol

Vlan1                  unassigned      YES unset  up                    up

FastEthernet1/0/1      10.0.0.1        YES manual up                    up

FastEthernet1/0/2      unassigned      YES manual down                  down

FastEthernet1/0/3      192.168.1.1     YES manual up                    up

R2# sh ip int brief
Interface              IP-Address      OK? Method Status                Protocol

Vlan1                  unassigned      YES unset  up                    up

FastEthernet2/0/1      10.0.0.2        YES manual up                    up

FastEthernet2/0/2      unassigned      YES manual down                  down

FastEthernet2/0/3      192.168.1.2     YES manual up                    up

FastEthernet2/0/4      unassigned      YES unset  down                  down

FastEthernet2/0/5      unassigned      YES unset  down                  down

FastEthernet2/0/6      unassigned      YES unset  down                  down

FastEthernet2/0/7      unassigned      YES unset  down                  down

FastEthernet2/0/8      unassigned      YES unset  down                  down

FastEthernet2/0/9      unassigned      YES unset  down                  down

FastEthernet2/0/10     unassigned      YES unset  down                  down

FastEthernet2/0/11     10.1.23.2       YES manual up                    up

Can you please explain me As R1 and R2 are connected via Fas int so in this case why we need network command

network 192.168.1  on R2  to advertise this route to R3 ?

Regards

MAhesh

[Richard Burts · Accepted solution]

Mahesh

If you do not use the network command for 192.168.1.0 then EIGRP will not run on that interface. And in that case it looks to me like the routers would not be neighbors.

HTH

Rick

[InayathUlla Sharieff · Accepted solution]

Hi Mahesh,

The network statement in EIGRP is less about what is advertised and more about what interfaces are participating.  So the network statement is by default classful, but we can add the wildcard mask.

You need to explicity advertise the network if you want that to be populated over to the EIGRP AS.

For example:

If you dont advertise the networks on the routers, how will routers share there topology infomration with the other routers in the EIGRP domain?

Hence what ever network you want that to be visible to others in the same EIGRP AS then you need to advertise it on the router to get it populated over the other routers.

EIGRP will be run on that interface.

Take your scenario:

==============

R1---R2

R1#sh ip int brief
Interface              IP-Address      OK? Method Status                Protocol

Vlan1                  unassigned      YES unset  up                    up

FastEthernet1/0/1      10.0.0.1        YES manual up                    up

FastEthernet1/0/3      192.168.1.1     YES manual up                    up

R2# sh ip int brief
Interface              IP-Address      OK? Method Status                Protocol

Vlan1                  unassigned      YES unset  up                    up

FastEthernet2/0/1      10.0.0.2        YES manual up                    up

FastEthernet2/0/3      192.168.1.2     YES manual up                    up

FastEthernet2/0/11     10.1.23.2       YES manual up                    up

In this case:

if you just have the eigrp configuration as below then you would not be able to see any routes in eigrp topology:

R1(config-if)#router eigrp 200

R1(config-router)#network 10.0.0.1

R2(config-if)#router eigrp 200

R2(config-router)#network 10.0.0.2 >>> This is to be run to form the EIGRP neigbors.

*Mar  1 00:43:07.575: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 10.0.0.1 (Serial0/0) is up: new adjacency

*Mar  1 00:43:08.423: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 10.0.0.1 (Serial0/0) is resync: summary configured

They will just form neighbors and  sharing there complete topology information as nothing has been advertise.

Scenaori:

I have not advertise any network on R1 except 10.X hence this is the info you see in the routing table of R2:

R2#sh ip route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 1 subnets

C       10.0.0.0 is directly connected, Serial0/0

2-

Now I will advertise some network on R1

R1(config)#router eigrp 200

R1(config-router)#network 192.168.0.1 >> 192.X.x.x network advertised:

EIGRP update will be propogated across AS 200 domain and all the routers part of that domain will recieve this network.

check the route on R2:

R2#sh ip route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 1 subnets

C       10.0.0.0 is directly connected, Serial0/0

     192.168.0.0/32 is subnetted, 1 subnets

D       192.168.0.1 [90/2297856] via 10.0.0.2, 00:00:32, Serial0/0  >>> This route is learned now.

Hope this clarifies your doubt.

Regards

Inayath

Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[mahesh18]

Hi Inayath,

One last thing in on this

IF we want to advertise the route to EIGRP domain -----

1>IF we want to advertise the loopback IP of R1  to say 4  routers all are in same AS  then we only need to run the

network command on R1.

2>IF we want to advertise the IP address of say fast ethernet of R1  which connects to R2  then we need to config  the

network command with interface IP on all the routers say R1,R2 R3  right?

Regards

MAhesh

[InayathUlla Sharieff · Accepted solution]

Hi Mahesh,

1>IF we want to advertise the loopback IP of R1  to say 4  routers all are in same AS  then we only need to run the

network command on R1.

Answer: Yes you are understanding is correct. This is explained and example showed  in my first post.

2>IF we want to advertise the IP address of say fast ethernet of R1  which connects to R2  then we need to config  the

network command with interface IP on all the routers say R1,R2 R3  right?

Answer: Yes perfectly to indicate that you are running EIGRP process for that respective interfaces.

Please see my first post I have clearly documented with example.

HTH

Regards

Inayath

*Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[mahesh18]

Hi Inayath & Everyone,

Many thanks to everyone for putting there Inputs to this post.

Best regards

Mahesh