[cisco-voip] asymetrical routing and voice - thoughts? requirements?

Thu Oct 14 12:25:57 EDT 2010

Have you considered the backup interface command?

!
int fa0/0
  backup interface Fast Ethernet 1/0
!

The only alternative I can think of  might involve attaching a route-map, but then you have to consider changing the metric of both inbound and outbound routes on a per-interface basis.

Regards

James.

________________________________
From: cisco-voip-bounces at puck.nether.net [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Lelio Fulgenzi
Sent: 13 October 2010 21:48
To: Wes Sisk
Cc: voyp list
Subject: Re: [cisco-voip] asymetrical routing and voice - thoughts? requirements?

a very rudimentary diagram follows.

Essentially, any traffic that hits core-1 will go to the VG224:fa0/0 interface and any traffic that hits core-2 will go to the VG224:fa0/1 interface. That's because an interlink between the two cores (not pictured, sorry) increases the distance to the other side.

We are using intermediary switches because there are not enough ports on the core switches/routers.

The links are essentially layer three routed point-to-point links (through a layer two interface).

The default route is sent to the VG224 using eigrp summary command and they are equally weighted. So traffic outbound from the VG224 will be random across both links. I can change this by using a delay command easily to prefer one route over the other. But again, this will affect outbound traffic only.

I guess there's a difference between equal routes (which appear on the VG224) which means traffic to the same destination will traverse both links and with an asymetrical route which I understand as traffic to a device goes out one link and comes back on another. However, I can't guarantee that traffic from a device on the network will always choose core-1 or core-2, so it may be a case of inbound traffic coming in on either interface as well.[cid:841102416 at 14102010-13EF]

---
Lelio Fulgenzi, B.A.
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Cooking with unix is easy. You just sed it and forget it.
                              - LFJ (with apologies to Mr. Popeil)

________________________________
From: "Wes Sisk" <wsisk at cisco.com>
To: "Lelio Fulgenzi" <lelio at uoguelph.ca>
Cc: "voyp list" <cisco-voip at puck.nether.net>
Sent: Wednesday, October 13, 2010 4:29:18 PM
Subject: Re: [cisco-voip] asymetrical routing and voice - thoughts? requirements?

We're missing a bit of information like how you got asymmetrical routing to the router interfaces.  Care to share?

Otherwise, in theoretical discussion, my peers agree that router will service traffic for any locally configured IP from any network interface.

There are the classic issues of binding VOIP protocols to interfaces with routable IP addresses but that is a separate issue.

/Wes

Lelio Fulgenzi wrote:
OK, not sure if this has been discussed before, but I just tried to get all my voice through one interface of my VG224 and in doing so, I lost the route to the other interface. We did this by using the delay command. Anything else I've been told, will take significant time to deploy.

So the question is, in the case of end devices (mainly gateways) that have two uplinks, how important is it to ensure that only one side is always used? Is it a requirement or is it a nice to have? I'd rather not be introducing delay statements if I don't have to.

Or is it all just to make troubleshooting easier?

---
Lelio Fulgenzi, B.A.
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Cooking with unix is easy. You just sed it and forget it.
                              - LFJ (with apologies to Mr. Popeil)

________________________________

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