ip summary address

[carl_townshend]

when i do this on an interface for eigrp, say I have the 10.1.0.0/16 and the 10.2.0.0/16 on my eigrp networks, would I just set these 2 to be advertised as individuals or just the 10.0.0.0/8 network and if I advertised these as individual networks on both the interfaces would I do ip summary address eigrp xxx 10.0.0.0 255.0.0.0

I am a little unsure of this command, I was told it was always best to summarise my networks, but at the same time wouldnt I be doing this is if just did eigrp xxx, network 10.0.0.0/8 ?

thanks all

[Patrick Laidlaw]

Carl,

It really depends on your network size on sumarization. If you have a bunch of networks that have the same path and only one path then yes summarise. Eigrp does a fairly good job of taking care of summarys by it self and really doesn't need much tweaking unless your running a fairly complex network.

On your other question about advertising networks. When ever you type in the network command for eigrp it looks to see what interfaces are attached to fit into that network and then advertises them with there mask. Example.

Lets say you have the two above network 10.1.0.0/16 and 10.2.0.0/16 and type in "network 10.0.0.0" into your eigrp process. Your router will automatically know that 10.0.0.0 is a class A network it will then look to see if any interfaces have a 10 network attached to them. Since you have 10.2 and 10.1 it will advertise those networks into the routing process with the masks so your neighbors routing table for eigrp will have the following routes.

D 10.1.0.0/16

D 10.2.0.0/16

You won't see a 10.0.0.0/8 in there tables just the two networks that were attached to your interfaces.

Patrick

[carl_townshend]

so could i summarise on each interface to the 10.0.0.0/8 network, can anyone give me an example where I should summarize ?

[Patrick Laidlaw]

Carl,

Lets say you have the following networks 10.0.0.0/16, 10.1.0.0/16, 10.2.0.0/16, 10.3.0.0/16, 10.4.0.0/16, 10.5.0.0/16

Interfaces with the following Addys

Lo0 10.0.0.1/16

Lo1 10.1.0.1/16

Lo3 10.2.0.1/16

Lo3 10.3.0.1/16

F0/0 10.4.0.1/16

F0/1 10.5.0.1/16

Your routing process.

router eigrp 100

network 10.0.0.0

This advertises all your networks into the routing process. Places we could summarzie would include FA0/0 and fa0/1 with "ip summary-address eigrp 100 10.0.0.0 255.252.0.0" This would summarize the networks 10.0 - 10.3 as a single network to the neighbors on FA0/0 and FA0/1.

EIGRP will show a summary route of 10.0.0.0/14 in the routing tables.

Hope this helps if it solves your problem let me know.

Patrick

[carl_townshend]

Hi There, So if I advertised the 10.0.0.0/8 network and put my interfaces in a 10.2.0.0 and 10.3.0.0/16 networks, does eigrp look at the masks on the interfaces and advertise the routes with that mask, Am I right in saying if I wanted I could advertise the 10.2 and 10.3 networks in the eigrp network statement ?

thanks

[carl_townshend]

So this is basically summarising on its own, why wouldnt we advertise both 10.1 and 10.2 networks seperately in the network statement ?, I gather for this also that auto summary has to be off ?

[carl_townshend]

hi all, just to add, if I wanted to propagate a default route from my internet router, Can I just put a ip summary-address eigrp 100 0.0.0.0 0.0.0.0 on that router, would this get pushed out to all my other routers so they would know the default toute out ?

thanks