EIGRP Question

jezg76

I have the following in a lab setup:

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I am running this using Dynamips with the 2691 for my 3 routers and a 3640 for my "switch".

This is happening during my first EIGRP lab in the new Cisco Lab Porfolio book.

My question is on why Router 3 (with the Loopback3 interface) is not adding the alternate path through the serial link (bandwidth 64k) as the other 2 routers are. Here are the results of all 3 routers' show ip eigrp topology all-links command:

R1:

R1#sh ip eigrp topology all-links
IP-EIGRP Topology Table for AS(1)/ID(10.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.1.3.0/24, 1 successors, FD is 156160, serno 4
        via 10.1.100.3 (156160/128256), FastEthernet0/0
        via 10.1.200.2 (40642560/156160), Serial1/0
P 10.1.2.0/24, 1 successors, FD is 156160, serno 30
        via 10.1.100.2 (156160/128256), FastEthernet0/0
        via 10.1.200.2 (40640000/128256), Serial1/0
P 10.1.1.0/24, 1 successors, FD is 128256, serno 2
        via Connected, Loopback1
        via 10.1.200.2 (40642560/156160), Serial1/0
P 10.1.100.0/24, 1 successors, FD is 28160, serno 1
        via Connected, FastEthernet0/0
        via 10.1.200.2 (40514560/28160), Serial1/0
P 10.1.200.0/24, 1 successors, FD is 40512000, serno 10
        via Connected, Serial1/0
        via 10.1.100.2 (40514560/40512000), FastEthernet0/0

R2:

R2#sh ip eigrp topology all-links
IP-EIGRP Topology Table for AS(1)/ID(10.1.2.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.1.3.0/24, 1 successors, FD is 156160, serno 40
        via 10.1.100.3 (156160/128256), FastEthernet0/0
        via 10.1.200.1 (40642560/156160), Serial1/0
P 10.1.2.0/24, 1 successors, FD is 128256, serno 2
        via Connected, Loopback2
        via 10.1.200.1 (40642560/156160), Serial1/0
P 10.1.1.0/24, 1 successors, FD is 156160, serno 39
        via 10.1.100.1 (156160/128256), FastEthernet0/0
        via 10.1.200.1 (40640000/128256), Serial1/0
P 10.1.100.0/24, 1 successors, FD is 28160, serno 38
        via Connected, FastEthernet0/0
        via 10.1.200.1 (40514560/28160), Serial1/0
P 10.1.200.0/24, 1 successors, FD is 40512000, serno 11
        via Connected, Serial1/0
        via 10.1.100.1 (40514560/40512000), FastEthernet0/0

R3:

R3#sh ip eigrp topology all-links
IP-EIGRP Topology Table for AS(1)/ID(10.1.3.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.1.3.0/24, 1 successors, FD is 128256, serno 2
        via Connected, Loopback3
P 10.1.2.0/24, 1 successors, FD is 156160, serno 23
        via 10.1.100.2 (156160/128256), FastEthernet0/0
P 10.1.1.0/24, 1 successors, FD is 156160, serno 3
        via 10.1.100.1 (156160/128256), FastEthernet0/0
P 10.1.100.0/24, 1 successors, FD is 28160, serno 1
        via Connected, FastEthernet0/0
P 10.1.200.0/24, 2 successors, FD is 40514560, serno 13
        via 10.1.100.1 (40514560/40512000), FastEthernet0/0, serno 10
        via 10.1.100.2 (40514560/40512000), FastEthernet0/0

Forgive me for not labeling the routers, but the Loopback interface on all the routers matches the hostname.

R3 just is not making sense to me. The other 2 routers are showing the alternate paths in the command, but why does it not show on R3?

For instance, shouldn't network 10.1.2.0/24 also have a listing through R1's FA0/0 (10.1.100.1) listing a metric of (40642560/40640000). This using the least-bandwidth value of 64 kbps and a sum of 2510 for the delay (2000 serial link, 10 100Mbps link, 500 on Loopback2).

Any ideas why this is not being recorded? Any thoughts would be greatly appreciated.

EdTheLad

I just did a quick lookup on the ccna requirements as i was sure eigrp was part of the ccna.Anyway i was right "Configure, verify, and troubleshoot EIGRP".
Maybe you were lucky during your exam and there was no eigrp? do you know anything about the feasible condition? or what eigrp is all about?

jezg76

I understand the feasible condition. The Advertised Distance of the neighbor router must be less than the current Successor's Feasible Distance for it to be considered a Feasible Successor route.

I am not sure how this relates to my question, though. I just want to know why it is not adding a route with the all-links command added to the end of show eigrp topology. I assumed the all-links would add all the routes, regardless if it is a FS or not.

I do appreciate your comments insulting my intelligence. Thanks for you response, though.

mikej412

jezg76 wrote:

I assumed the all-links would add all the routes, regardless if it is a FS or not.

EIGRP isn't a link state routing protocol. An EIGRP router doesn't know about or maintain the topology of the entire AS.

jezg76

mikej412 wrote:

jezg76 wrote:

I assumed the all-links would add all the routes, regardless if it is a FS or not.

EIGRP isn't a link state routing protocol. An EIGRP router doesn't know about or maintain the topology of the entire AS.

That I get. It is an "advanced distance vector" protocol, so it does exhibit aspects of both distance vector and link-state protocols.

It does keep its directly connected neighbor's routes in its topology table, correct? So, with it being directly connected to R2, it should know about paths through the serial connection. Is that not a correct assumption? If I am wrong then I guess it's back to the basics.

Maybe I am just misunderstanding what this command does. show ip eigrp topology will only show you successor and feasible successor routes, while I am assuming the all-links addition to this command would add all the links, even if it is not a successor or a FS. Maybe that is where I am getting hung up...

Thanks mikej for the input!

mikej412

That "advanced distance vector" thing is marketing-speak.

jezg76 wrote:

If I am wrong then I guess it's back to the basics.

I think that was Ed's point, but stated un-diplomatically.

EIGRP gets its neighbor's best routes and puts them in its topology table.

EdTheLad

mikej412 wrote:

That "advanced distance vector" thing is marketing-speak.

jezg76 wrote:

If I am wrong then I guess it's back to the basics.

I think that was Ed's point, but stated un-diplomatically.

EIGRP gets its neighbor's best routes and puts them in its topology table.

Yes, i'm bad , the original question should have been more specifc referring to the all-links command.Anyway all routes should be seen in the topology table even if the feasible condition isnt met.The only time a route isnt seen is if it is invalid due to split-horizon.
I dont have tiime to setup but my idea on whats happening is as follows:
In your topology R1 is learning the lo2 route via the ethernet interface,a poison reverse will be sent back in this direction which will be received on R3.R3 hence will not include this route in the topology table.If you run some debugs im pretty sure you will see this.

jezg76

EdTheLad wrote:

Yes, i'm bad , the original question should have been more specifc referring to the all-links command.

My original post stated:

My question is on why Router 3 (with the Loopback3 interface) is not adding the alternate path through the serial link (bandwidth 64k) as the other 2 routers are. Here are the results of all 3 routers' show ip eigrp topology all-links command:

I guess I could have been super specific as opposed to more specific. I do thank you both for your help, but I will take my CCNA and go back to the little boys board since obviously I am not ready for asking the type of questions needed to be asked on here by someone just diving into NP stuff.

My only hope is when I do get my CCNP I don't morph into an arrogant ahole.

Happy New Year.

networker050184

Woah your response is uncalled for.

This isn't the little boys board, it's professionals giving their opinions on a public forum. People are not here to teach you, but most do not mind helping out. If you get an opinion you don't like you just take it with a grain of salt and realize YOU asked for peoples opinions. Don't let it discourage you, ask if you have a queation. Just be prepared to be bashed if it is something simple, because like you said, its not the little boys board.