EIGRP Question

Robbo777

Hi, i wanted to ask a question about how EIGRP works. Basically, does EIGRP only form routes that start by having default gateways. What I'm trying to say is if I have

192.168.1.1 on one interface on a router
10.10.11.1 on another on the same router

BUT also have another machine linked up to the switch that connects to the router with an IP of 10.10.11.1, will EIGRP not form a route with this computer because it does not have a default gateway to start with on the router?

Strange one but i was messing around before and created this type of topology and no relationships where formed with 10.10.11.1 because it couldn't get to the router even though the hello packets from EIGRP where getting to the PC.


Thanks for the help.

networker050184

You don't run EIGRP with a computer so it doesn't matter if it has a default gateway or not.

Robbo777

No that's not what i meant or said, i meant if you have another computer with an IP etc.. but cant get to the default gateway because its not in the same subnet or its not set etc... then will the EIGRP hello messages still pick up that address and put it in its route table? Basically

router
fa0/0 192.168.1.1
fa0/1 10.10.10.1

PC1
IP: 192.168.1.10
gateway: 192.168.1.1

PC2
IP: 10.10.10.10
Gateway: 10.10.10.1

PC3
IP: 10.10.11.10
Gateway:


EIGRP
network 10.10.0.0 0.0.255.255
no auto summary

So........will EIGRP not pick up the 10.10.11.10 route/subnet because its not initially going to the router because it either doesn't have a default gateway or the default gateway is not in the correct subnet? From what I've played around with the answer is no! But i wanted to make sure that i just wasn't doing anything wrong to.

Cheers

networker050184

You have a very bad misunderstanding of how EIGRP works. It doesn't pick things up in hello messages for advertisement. It's completely autonomous from a PC and if it has a gateway or not.

cpartin

EIGRP isn't going to form a neighbor relationship with a PC. The PC may see hellos from the router but it's not going to return them, so no relationship will be formed. Only devices which speak EIGRP and match the requirements (same AS, K values, authentication etc) will be added as neighbors.

volfkhat

cpartin wrote: »

EIGRP isn't going to form a neighbor relationship with a PC. The PC may see hellos from the router but it's not going to return them, so no relationship will be formed. Only devices which speak EIGRP and match the requirements (same AS, K values, authentication etc) will be added as neighbors.

Great explanation :]

And Good question for beginners working to learn the basics~

Robbo777

cpartin wrote: »

EIGRP isn't going to form a neighbor relationship with a PC. The PC may see hellos from the router but it's not going to return them, so no relationship will be formed. Only devices which speak EIGRP and match the requirements (same AS, K values, authentication etc) will be added as neighbors.

I don't think "networker050184 " understood my question. I know EIGRP forms neighbours with other routers because they run EIGRP as well. That wasn't my question, my question was will EIGRP SEE the address of 10.10.11.10 without it having a default gateway on the routers interfaces to start with. From my experience before messing around with it and from the example I gave, the answer is no. But I was wondering if someone could provide an explanation for this.

My best guess would be because the router doesnt have any evidence that the route exists and there is no ARP evidence that it exists either. But i'm still a bit curious as to what the PC does with the hello messages EIGRP sends it. For example why does it register the other 2 routes of 192.168.1.10 and 10.10.10.10 and not 10.10.11.10 is basically what I'm asking, what's the difference?

Legacy User

Robbo777 wrote: »

But i'm still a bit curious as to what the PC does with the hello messages EIGRP sends it. For example why does it register the other 2 routes of 192.168.1.10 and 10.10.10.10 and not 10.10.11.10 is basically what I'm asking, what's the difference?

@Robo
Dude your post is extremely confusing. To clarify the PC does not do anything with the hello packet from EIGRP. EIGRP hello packets are only sent from within the same EIGRP logical group that has EIGRP enabled on the interface.

Forget the fact that you have EIGRP running. You need to understand at the PC level without a default gateway the PC does not know where to send traffic to. Dude stop wasting your time and learn how EIGRP works at a router level.

late_collision

Robbo777 wrote: »

my question was will EIGRP SEE the address of 10.10.11.10 without it having a default gateway on the routers interfaces to start with.

No, because EIGRP doesn't deal in addresses, it deals in networks. EIGRP wont SEE anything other than neighbors from which it receives a HELLO. The fact that PC3 has a default gateway or not has no bearing on what the router (or EIGRP) does.

If you're asking, will "router" be able to communicate with "PC3", then the answer is no, because "router" doesn't have an interface in the same network (subnet) as "PC3".

Robbo777 wrote: »

For example why does it register the other 2 routes of 192.168.1.10 and 10.10.10.10 and not 10.10.11.10 is basically what I'm asking, what's the difference?

What do you mean registers the routes? Are you asking why "router" can communicate with "PC1" and "PC2" but not "PC3"? If so, the answer is because "router" has an interface with an address on the same network (subnet) as "PC1" and "P2". It does not have an address on the same network (subnet) as "PC3".


Edit: I should back this up some and ask what are the subnet masks on your router interfaces.

Phileeeeeeep651

So on your router you have networks 192.168.1.0 and 10.10.10.0, those are the only networks that EIGRP will advertise.

EIGRP will only know about networks on the routers so, regardless of your command 10.10.0.0 0.0.255.255, EIGRP will not see 10.10.11.0 network because there is no interface associated with that network.

Robbo777

Phileeeeeeep651 wrote: »

So on your router you have networks 192.168.1.0 and 10.10.10.0, those are the only networks that EIGRP will advertise.

EIGRP will only know about networks on the routers so, regardless of your command 10.10.0.0 0.0.255.255, EIGRP will not see 10.10.11.0 network because there is no interface associated with that network.

Thank You! This was a difficult tricky thing to get out and actually explain but that's all i needed clarity on finally! Haha, cheers dude.

Robbo777

late_collision wrote: »

No, because EIGRP doesn't deal in addresses, it deals in networks. EIGRP wont SEE anything other than neighbors from which it receives a HELLO. The fact that PC3 has a default gateway or not has no bearing on what the router (or EIGRP) does.

If you're asking, will "router" be able to communicate with "PC3", then the answer is no, because "router" doesn't have an interface in the same network (subnet) as "PC3".

Thanks for the clarity, it was tricky to explain.

Robbo777

dmarcisco wrote: »

@Robo
Dude your post is extremely confusing. To clarify the PC does not do anything with the hello packet from EIGRP. EIGRP hello packets are only sent from within the same EIGRP logical group that has EIGRP enabled on the interface.

Forget the fact that you have EIGRP running. You need to understand at the PC level without a default gateway the PC does not know where to send traffic to. Dude stop wasting your time and learn how EIGRP works at a router level.

I know it was confusing and tricky to explain but I'm not wasting my time with these queries, thanks anyway