EIGRP ip summary-address

[brandon02852]

Hello,

I am doing some network consulting for a college that has three campuses.  There are numerous L3 links that connect the campus cores and the various MDF's at each campus.

I am noticing that each SVI that participates in routing has the following commands:

• ip summary-address eigrp 179 10.0.0.0 255.255.0.0

• ip summary-address eigrp 179 172.16.0.0 255.240.0.0

• ip summary-address eigrp 179 192.168.0.0 255.255.0.0

Now this seems ridiculous.  Why should each SVI that participates in routing have these three commands?

Here is the EIGRP configuration on this particular campus core

router eigrp 179

network 0.0.0.0

redistribute static route-map eigrp-redistribute

offset-list default-route out 24200 Vlan2517

passive-interface default

no passive-interface Vlan5

no passive-interface Vlan2517

no passive-interface Vlan3000

no passive-interface Vlan3002

no passive-interface Vlan3003

no passive-interface Vlan3005

no passive-interface Vlan3007

no passive-interface Vlan3008

no passive-interface Vlan3010

no passive-interface Vlan3012

eigrp router-id 10.0.0.2

The prefix list redistributes a wide range of subnets (172.16.0.0/16, 172.30.0.0/16, 192.168.0.0/16...etc).

Now I would figure you just advertise the IP addresses of these SVIs used for routing with the network statement.

Thank you for any insight you can provide!

[Philip D'Ath]

That smells a bit like a config where there is another second routing protocol is in use somewhere.  Is this the case? Perhaps it used to be the case?

[brandon02852]

Good afternoon Phillip,

Thanks for the fast response.  To my knowledge, they are only using EIGRP and have only ever used EIGRP.  I will ask the senior administration and post a response when I have more information.

[Jon Marshall]

You need to draw out the topology per campus and then check the routing tables of each L3 switch.

Those summary addresses are suppressing any more detailed routes so they may be trying to keep the routing tables to a minimum on the L3 devices in each building although why not just use a default route if that is the case.

They may also have multiple paths between L3 devices and again you need to draw this out to get a full understanding of the reasoning behind it.

With the information you have provided it's not possible to say why it has been done this way.

Jon