Subject: Re: [VRRP] Routing table in VRRP

From: Radia Perlman <[email-masked]>
Date: Thu, 25 Sep 2003 14:11:32 -0700 (PDT)

I don't believe there's any way to fix it. A is as sure it can reach
the prefix as B is. So it's hard to be able to do "better cost".

For instance, a repeater could go down, partitioning the LAN, so
really A and B *can* both reach the prefix. This is just a messy,
pain-in-the-neck kind of failure that is hard to diagnose
and makes weird things happen.

Radia

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From: Mudhafar Hassan-Ali <[email-masked]>
Date: Thu, 25 Sep 2003 20:02:37 -0700

Radia,

Does it make sense to fix this issue in the VRRP draft by introducing a
mechanism for the master to detect a link outage?

Mudhafar

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From: Ben Black <[email-masked]>
Date: Thu, 25 Sep 2003 20:00:15 -0700

Other than via mechanisms not generally seen outside a Harry Potter book,
how do you propose the routers detect such a layer 2 partitioning?

Ben

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From: Mudhafar Hassan-Ali <[email-masked]>
Date: Thu, 25 Sep 2003 21:30:20 -0700

Layer 2 mechanism should work just fine, do know any one that will do the
trick?

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From: "Don Provan" <[email-masked]>
Date: Fri, 26 Sep 2003 09:53:19 -0700

The question that each router needs to answer is, "Can I get
to what's important in this network?" The VRRP peer, being
redundant to the current system, is the one thing in the
network that clearly is NOT important. This suggests that
logically VRRP has nothing to do with solving this problem.

The obvious solution is to configure one or more "key nodes",
and then monitor them with ping and/or arp. If you lose contact
with all of them, you assume you've lost touch with the network,
and you stop advertising your route to it.

-don

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of
> Mudhafar Hassan-Ali
> Sent: Thursday, September 25, 2003 9:30 PM
> To: Ben Black
> Cc: Radia Perlman; [email-masked]
> Subject: Re: [VRRP] Routing table in VRRP
>
>

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From: Mudhafar Hassan-Ali <[email-masked]>
Date: Sat, 27 Sep 2003 11:49:06 -0700

But that defeats the "redundancy" concepts that VRRP allegedly supports.
Without such a mechanism integrated as part of VRRP, we are allowing "silent
failures" to occur, which, to me, is very much like allowing loops in the
network to occur.

Mudhafar

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From: Ben Black <[email-masked]>
Date: Sat, 27 Sep 2003 18:26:04 -0700

VRRP, like any other useful protocol, does not solve all problems.  It
achieves exactly what is required of it.  The failure scenario we have
been discussing is a fact of life with Ethernet.  I do not want to attempt
any further extension of VRRP to handle such a situation.

Have you considered that with a subnet partitioned, there is no way to
determine which side of the partition should be considered "reachable"?
What happens when the partitioning leaves 50 hosts able to communicate with
router A and 50 hosts able to communicate with router B, but A and B are
unable to communicate with each other via VRRP on the subnet?

The short answer is design a better network.  Actually, that's the long
answer, too.

Ben