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Will EIGRP form a neighbor with stanby address?

We have two core 6509's connected to several distribution layer switches all of which are running EIGRP, the core switches are connected to a PIX which is the gateway to the internet. We are currently running HSRP between the core switches and the standby address is the gateway of last resort for the distribution layer switches. Is this the right way to do this or should we just configure the PIX to be the gateway of last resort? Also how does EIGRP deal with the standby address being its neighbor?

7 REPLIES
Hall of Fame Super Gold

Re: Will EIGRP form a neighbor with stanby address?

Harold

It is difficult to give a really good answer without knowing a bit more about your environment. But in general I would say that it is good for the distribution layer switches to use the standby address as their gateway of last resort.

EIGRP does not deal with the standby address. Each router will send hello messages sourced from its configured address and will form neighbor relationship with the neighbors configured address. The standby address does not affect this.

HTH

Rick

Community Member

Re: Will EIGRP form a neighbor with stanby address?

Rick,

I have included a drawing and other than using HSRP I was going to configure:

ip route 0.0.0.0 0.0.0.0 (Pix Address)

redistribute static

on both the core switches. Do you still feel that HSRP is still the way to go?

Community Member

Re: Will EIGRP form a neighbor with stanby address?

Drwaing for post above.

Hall of Fame Super Gold

Re: Will EIGRP form a neighbor with stanby address?

Harold

ok. now I have seen the drawing and there is not anything that I see there that would change my opinion about the advantages of using HSRP.

For anything that is in the VLAN where the PIX is, it would be good to configure the PIX address directly. But for anything connected in a different VLAN (where they will have to use a gateway address) I believe that HSRP provides significant advantages as compared to configuring the PIX address directly.

HTH

Rick

Hall of Fame Super Gold

Re: Will EIGRP form a neighbor with stanby address?

Harold

The drawing did not seem to make it into the post, so I am not sure what your environment is. Assuming that there is more than one VLAN present I still am inclined to advocate the use of HSRP. I think we can consider several aspects of this question. When your original post referred to using the standby as the default gateway for the distribution switches I am not clear whether you meant literally that the distribution switches would be configured with a gateway address of the standby or whether you meant that end stations connected to the switches would use the standby address. Especially from the standpoint of the end stations I believe that the standby address is an advantage. You could configure the end stations with a gateway using the PIX address. But if you do you will be depending on proxy ARP for all the VLANs that are not locally connected to the PIX (and that is likely to be all of the user VLANs). Not only do I consider relying on proxy ARP to be a weakness but you also should consider this scenario: an end station ARPs for its gateway address (the PIX address) and one of the switches will answer, and the MAC supplied will be the MAC of the switch. The end station now has a MAC for its gateway. If there is a problem and that particular switch becomes available then the gateway for the end station is not available until the end station clears it ARP entry and ARPs again.

So unless there is something about your environment that I do not understand I would be in favor of continuing to use the standby address.

hTH

Rick

Community Member

Re: Will EIGRP form a neighbor with stanby address?

Rick,

I I dont think I am making this clear, I apologize. The HSRP is configured between the core switches and the standby address is being used by the distribution switches as a gateway of last resort. There are is only one VLAN, with no hosts. This a layer 3 link between 27 routers, I am thinking purely of routing.

Thanks

Hall of Fame Super Gold

Re: Will EIGRP form a neighbor with stanby address?

Harold

You are right that I did not clearly understand the environment that you were talking about. If there truely is only one VLAN (and that means that the PIX is in the same VLAN as the switches) then the gateway does not come into play. If there is only one VLAN then everything is local, every station (switch) ARPs for the destination address they need and gets a response from the destination machine - no gateway comes into play.

At the point where there is more than one VLAN then I think that HSRP potentially has some advantages. But not for a single VLAN.

HTH

Rick

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