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EIGRP/RIP AND SECONDARY IP ISSUES

I have two different links connecting to my cisco 1750 box through an ethernet interface using secondary and primary ip address of different subnets. I can get only one link working at a time with rip or eigrp when i make it the primary ip. the link on secondary ip does not seem to get updates and routes.

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Gold

Re: EIGRP/RIP AND SECONDARY IP ISSUES

So, I've tried a couple of other options in the lab, and I don't see any other way of doing it, other than perhaps numbering your new mpls link in the same address space as the old point-to-point radio links. You can't create subinterfaces unless the interface is defined as a 1q link. I suppose you could put 1q on all of the interfaces on the point-to-point links, and over the mpls link, but I'm not certain how well those media will transport the 1q stuff. If you could do this, you could then run two different subinterfaces.

Another option is to try unnumbering the interface, but you can't unnumber a broadcast interface.

I don't think you can tunnel over the ppp radio links, since the end points have to be routable/reachable destinations. To do that, you'd have to add the new interface addresses into the routing table as reachable across the ppp radio links, which means, effectively, renumbering that link into the same address space as the mpls link, anyway.

You could try tunneling the other direction, across the mpls link, but you'll end up having to route your _other_ addresses across the mpls link. You'll need routing to work to get the tunnel to work, to get routing across the tunnel to work. You could rely on statics to get the tunnels up and running, but you still need a destination ip address, which involves creating new addresses, renumbering, or something along those lines. So, I'm not certain where tunneling will get you (?).

Russ.W

7 REPLIES
Gold

Re: EIGRP/RIP AND SECONDARY IP ISSUES

EIGRP will only form neighbor adjacencies across the primary interface address, never the secondary. RIP will only pay attention to updates received on the same subnet as the primary interface address. This is why you can only get routing information over the primary address.

But, I'm confused--are you saying that you have three routers, one on subnet a, one on subnet b, and the third on subnets a & b? Why not just give all three an address in subnet a, and make those the primary address, and then give all three an address in subnet b, making those the secondary addresses? It's not going to matter which address routing actually runs on, as long as all the subnets are reachable from the right routers... (?).

Russ.W

New Member

Re: EIGRP/RIP AND SECONDARY IP ISSUES

can i get eigrp and rip updates with tunnel interface

Gold

Re: EIGRP/RIP AND SECONDARY IP ISSUES

You'd like to tunnel over the broadcast interface to exchange routing information? You could, I suppose, set up the tunnel with the current secondary address, but then hosts which are attached to the ethernet, using an address from the secondary range, are not going to be able to send traffic off segment....

Could you explain what you are actually trying to do a bit? Maybe there's a better way to do it?

Russ.W

New Member

Re: EIGRP/RIP AND SECONDARY IP ISSUES

What i'm trying to do is to cut-over from a link using (cylink radios) PP multlink to an MPLS (FWA) cloud for routing my packets. However, i would like to retain the other link and make the cut-over transparent to users. Find below my configuration:

Router A

int f0/0

ip add 10.16.x.1/24 (link through MPLS Cloud)

int f0/1

ip add 149.1.1.x/16

Router B

Int f0/0

Ip add 10.24.x.2/24 secondary (link through MPLS Cloud)

Ip add 150.54.9.1/16 (link through PPP Multilinks)

Ubr925 A

Ip add 10.16.x.1/24 (link through MPLS Cloud)

ubr925 B

ip add 10.24.x.1/24 (link through MPLS Cloud)

Gold

Re: EIGRP/RIP AND SECONDARY IP ISSUES

Okay, so I see the problem, but I'm not certain you can solve it this way. Could you renumber the ppp link across the radios into the 10.24 range of addresses, so all the interfaces will be in the same subnet?

You could try subinterfaces on the fast ethernet interface, if that will work, but I've not tried it.

Russ.W

New Member

Re: EIGRP/RIP AND SECONDARY IP ISSUES

Hi Russ,

I would not like to renumber the ppp link. Is there an alternative?.

Gold

Re: EIGRP/RIP AND SECONDARY IP ISSUES

So, I've tried a couple of other options in the lab, and I don't see any other way of doing it, other than perhaps numbering your new mpls link in the same address space as the old point-to-point radio links. You can't create subinterfaces unless the interface is defined as a 1q link. I suppose you could put 1q on all of the interfaces on the point-to-point links, and over the mpls link, but I'm not certain how well those media will transport the 1q stuff. If you could do this, you could then run two different subinterfaces.

Another option is to try unnumbering the interface, but you can't unnumber a broadcast interface.

I don't think you can tunnel over the ppp radio links, since the end points have to be routable/reachable destinations. To do that, you'd have to add the new interface addresses into the routing table as reachable across the ppp radio links, which means, effectively, renumbering that link into the same address space as the mpls link, anyway.

You could try tunneling the other direction, across the mpls link, but you'll end up having to route your _other_ addresses across the mpls link. You'll need routing to work to get the tunnel to work, to get routing across the tunnel to work. You could rely on statics to get the tunnels up and running, but you still need a destination ip address, which involves creating new addresses, renumbering, or something along those lines. So, I'm not certain where tunneling will get you (?).

Russ.W

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