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RE: Routing loop [7:84050] posted 02/10/2004
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I'd strongly suggest checking for bugs.  Dunno about EIGRP, but I have seen
a similar thing with OSPF, which was an IOS bug (the route in question was
to a subnet that was previously valid - it did not just appear out of
nowhere but shouldn't have still been advertised).

I'm no expert in EIGRP - try digging into the EIGRP details to see where
it's coming from, not just the IP route table.  Does "Show ip eigrp
topology" give any more hints?

If it's anything like the OSPF bug (not that there's any reason it should be
:-), you may need to clear the routing process on a few of the routers, not
just the routes.

John Neiberger wrote:
> As someone else already mentioned, the route must originate from
> somewhere, and a router isn't going to originate a prefix that
> doesn't
> exist. If you're seeing it, then some router somewhere is
> advertising
> it. Try doing a "clear ip route *" on your routers and see if
> that
> helps. You've probably already done this, though.
> What model are these routers? And what version of IOS are you
> running?
> I'm beginning to wonder if you're seeing a bug, and a directly
> connected
> route that used to exist is still being advertised.
> John
> --
> >>> "TorZI-I/Brian Dunbar" 
> 2/9/04
> 11:08:01 AM >>>
> If the Subnet existed somewhere wouldn't one of the routers
> show the
> source?
> Each of these routers (in production) show each other as the
> source of
> the
> route when I do
> show ip route x.x.x.x EIGRP learns it from router A go to
> router A and
> type
> show ip route x.x.x.x it learns from another of the 6
> eventually it
> will hit
> back to the first router.
> -----Original Message-----
> From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx]On
> Behalf Of
> John Neiberger
> Sent: February 9, 2004 12:54 PM
> To: cisco@xxxxxxxxxxxxxx 
> Subject: Re: Routing loop [7:84050]
> >>>> TorZI-I/Brian Dunbar 2/9/04 10:48:58 AM >>>
> >I have an unusual routing loop that is hard to get rid of. The
> route
> is
> >learned by EIGRP from a circle of about 6 routers each refers
> to the
> other
> >as the source of the route.
> >
> >I put a static route on the central router to NULL0 and all 6
> routers
> >learned the route. Then I delete the null route 30 minutes
> later and
> the
> >route loop reappears. The routing loop is to an invalid subnet
> that
> does
> not
> >exist. May of existed at one point. None of the 6 routers
> refer to
> another
> >source for the route.
> >
> >Any ideas?
> I think the subnet must exist or the originating router
> wouldn't keep
> advertising it. Unless you're running into a really strange
> bug, a
> router is
> not going to originate a completely fictitious route. Can you
> give us
> some
> more details? Is this a lab or production environment?
> John
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