EIGRP network command

Answered Question

I have two routers on EIGRP

172.16.1.1(lo)---->R1(F0/0 192.168.1.1/24)<------------->(F0/0 192.1681.2/24)R2<-----10.10.1.1/24

172.16.2.1(l0)                                                                                             <----10.10.2.0/24

R1

====

Routing for Networks:

    172.16.0.0

    192.168.1.1/32

R2

========

Routing for Networks:

    10.10.0.0/16    <--------specified wildcard mask

    192.168.1.0

I have now eigrp running and all neighbours are formed....but with following routing table

R1

====

D       172.16.0.0/16 is a summary, 00:42:30, Null0

C       172.16.1.0/24 is directly connected, Loopback1

C       172.16.2.0/24 is directly connected, Loopback2

D    10.0.0.0/8 [90/156160] via 192.168.1.2, 00:42:25, FastEthernet0/0   <--------shouldn't this be 10.10.0.0/16?

C    192.168.1.0/24 is directly connected, FastEthernet0/0

R2

=====

D    172.16.0.0/16 [90/156160] via 192.168.1.1, 00:42:55, FastEthernet0/0

     10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks

C       10.10.1.0/24 is directly connected, Loopback1

C       10.10.2.0/24 is directly connected, Loopback2

D       10.0.0.0/8 is a summary, 00:52:02, Null0

C    192.168.1.0/24 is directly connected, FastEthernet0/0

why int R1 we have

D    10.0.0.0/8 [90/156160] via 192.168.1.2, 00:42:25, FastEthernet0/0   <--------shouldn't this be 10.10.0.0/16?

Need your help in understanding this. Thanks

I have this problem too.
0 votes
Correct Answer by milan.kulik about 6 years 4 months ago

Hi,

you need

router eigrp xxx

no auto-summary

command in your configs.

See http://www.cisco.com/en/US/customer/docs/ios/iproute_eigrp/configuration/guide/ire_cfg_eigrp_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1060541

for an example.

HTH,

Milan

Message was edited by: milan.kulik

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suryakant.chavan Sun, 09/12/2010 - 11:39

Hi Ravindra,

If you want to see the entry  10.10.0.0/16 under R1 then you should give the command no auto-summary under R2 .

that is

          Router eigrp As

          network 10.10.0.0 0.0.255.255

          no auto-summary.

Because though EIGRP is class less routing protocol , its default behaviour is classfull . If we have not given no auto-summary command  , it summaries its directly connected networks to their default class & advertise to their neighbour.

Hope this is helpful to you.

Regards,

Suryakant

So if i am not wrong. There are two things that a network command does

1> checks the interfaces within the defined Network command

2> advertises all networks/routes on those interfaces which come in the defined network command

3> if in the network command, even after adding the subnet mask it will round it to classful network [need your comments as cisco official guide says

If no wildcard mask is configured on the eigrp network command, the command enables EIGRP on all of that routes directly connected to the configured classful network]

4> to have the routes in particular subnet we have to use no auto-summary as router sub command

Giuseppe Larosa Sun, 09/12/2010 - 12:26

Hello Ravindra,

the EIGRP network command does not provide an aggregate address "automatically" matching the network command itself.

in your example you have network 10.10.0.0 0.0.255.255 but this only means that all interfaces whose IP address falls in 10.10.0.0/16 will have the associated IP subnet advertised and they will be able to build EIGRP neighborships.

with no auto-summary set on  router eigrp process you will see the IP subnets 10.10.1.0/24 and 10.10.2.0/24 and not 10.10.0.0/16

To see 10.10.0.0/16 you need to use the ip summary-address eigrp command in interface mode AND you need no auto-summary

Hope to help

Giuseppe

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