Jeff

Apologies for any confusion. Let me be more specific.

The network statement tells EIGRP which interface(s) to run EIGRP on. Once EIGRP has been started on this interface then the EIGRP process will advertise this network + subnet mask to any EIGRP neighbors. So

(172.16.5.1/24 - fa0/0) R1 (s0/0 - 192.168.5.1/24) -> (192.168.5.2/24 S0/0) R2 (fa0/0 - 172.16.6.1/24)

R1

router eigrp 1

network 192.168.5.0

no auto-summary

R2

router eigrp 1

network 192.168.5.0

no auto-summary

So with the above config each router will only know about it's directly connected networks but they will form an EIGRP neighborship between each other.

If you then add

router eigrp 1

network 172.16.5.0

+ config already on R1

then R2 will no have a route for 172.16.5.0 pointing to R1 and this will have be learned from EIGRP.

Does this make sense ?

Jon

Jeff

Perhaps it will make more sense if we can build a small example and talk about it. Perhaps this can get us started:

interface fastethernet0/0

ip address 192.168.5.1 255.255.255.192

interface fastethernet0/1

ip address 10.0.0.1 255.255.255.0

router eigrp 1

network 10.0.0.0

So this little example has 2 interfaces and 2 networks. The EIGRP configuration has 1 network statement. So EIGRP will look at its network statement and look for any interface that matches it. fastethernet0/1 does match and fastethernet0/0 does not match. So interface fastethernet0/1 is included in EIGRP and fastethernet0/0 is not included in EIGRP.

Then EIGRP looks at the interface and determines that it should advertise network 10.0.0.0/24. It will not advertise 192.168.5.0.

Then EIGRP sends hello messages on its included interfaces (fastethernet0/1). If it receives a proper hello in response then it will form an EIGRP neighbor relationship and will advertise to its neighbor.

So in a sense the network statement does both functions you asked about: it derives information about what to advertise (what to talk about) and it determines where it will talk (who to talk to).

Would it make the explanation even more complicated to talk about advertising routes in the table that are not locally connected?

HTH

Rick

Great. I see we all agree now. That was my under standing as well.

However here is what I'm seeing.

I have three routers (Ok I have 30, but lets look at 3 of them)

A - B - C

Router A has interfaces in both 10.0.0.0 and 192.168.0.0. Both are network statements in EIGRP

Router B has interfaces only in 10.0.0.0 However Both are network statements in EIGRP

Router C has interfaces only in 10.0.0.0 and only network for 10.0.0.0 statements in EIGRP

Router C is getting routes in the route table for 192.168.0.0 via EIGRP.

I don't understand why I would be seeing this.

Thanks Rick. I see that now. Someone else configured the EIGRP and I'm just trying to clean up the system.

So if all learned routes are advertised then to advertise a default route all I should have to do is set it on the firewall to redistribute a default route and then the whole network would get it.

The network is currently setup with a default route on each device that just points toward the core routers, then the cores know the real exit point.

..

Rick,

Thanks for the detailed explanation, this post was very helpful, and cleared alot of questions I had regarding EIGRP and its process. Thanks

Jeff

There are a couple of things that you might do about the point to point subnets. One alternative would be to write a distribute list out in EIGRP which could deny the point to point subnets and permit other routes. Another alternative might be to configure manual summarization and advertise a block of addresses rather than each individual address (this could be especially effective if the point to point links terminate on a single router and if the addresses of the subnets were assigned to form a contiguous block of addresses).

[edit] now that I look again at your post you say that the p2p links are in 10.99.0.0. So it would be easy to configure something like this:

ip summary-address eigrp 1 10.99.0.0 255.255.0.0

you would configure this under the interface rather than under router eigrp. You would do it on each interface where you have EIGRP neighbors who do not need to see the detail routes.

HTH

Rick

Here is a sample diagram. So Just add

ip summary-address eigrp 1 10.99.0.0 255.255.0.0 to every interface on the core and it would still show up, but as a single items and not the 80 I have now. (20 sites and 4 tunnels each)