Subject: Re: No DVMRP routes [ARS1412/SSC1388]

From: Bill Fenner <[email-masked]>
Date: Mon, 7 Jul 1997 08:21:32 PDT

>It seems that it does not send a neighbor probe back to broodjeham.

This is an intentional bug in IOS.  mrouted doesn't require neighbor
probes to consider the link up.

>If a tunnel to
>another Cisco with MBone connectivity (amsterdam6.router.surfnet.nl) is
>added and ip dvmrp unicast-routing is enabled on this tunnel, mr1.eindhoven
>does get all DVMRP routes from amsterdam6.router AND from broodjeham. If
>this new tunnel is removed then, mr1.eindhoven keeps receiving DVMRP routes
>from broodjeham and broodjeham finds that the tunnel is up.

Cool.  I think it's time to ask Cisco for help; sounds like a very strange
bug.

  Bill

---

From: [email-masked] (Lukas Wunner)
Date: Sun, 13 Jul 1997 20:10:27 +0200 (MET DST)

Howdy,

>from broodjeham and broodjeham finds that the tunnel is up.

I just set up a tunnel between a Cisco 4500 running 11.2(2) and a Linux box
running mrouted 3.8 w/ Brad Parker's modifications and I encountered the
same behaviour.

Obviously the only DVMRP messages that the Cisco sends to its peers are
route announcements (i.e., no probes); if the Cisco knows about no
routes, it won't send *anything* to its peers.
mrouted on the other hand considers the link down upon starting up until
the first DVMRP message is received from the peer.

The workaround is to have the Cisco advertise at least one route to mrouted
and to wait a few seconds until mrouted has realized it has a new neighbour.
(e.g. "ip dvmrp default-information originate", which is dangerous
however if one of the two machines have MBONE connectivity)
In your case, opening another tunnel to amsterdam6 yielded the same effect.

	Lukas.

-- 
lukas wunner         unix, internetworking and security engineer
[email-masked]      LW26-RIPE      http://www.wunner.de/~lukas/
"Those who do not understand Unix are condemned to reinvent it, poorly."
                                               --  Henry Spencer