[nsp] IP-EIGRP: Neighbor A.B.C.D not on common subnet...

[Oliver Boehmer (oboehmer)]

Hi Yuval,

if the Catalyst (or any other switch for this matter) is flooding the
multicast out to another vlan port this is a severe bug and needs to be
addressed. Can you connect a sniffer and verify this assumption?
I would not ignore this problem as it points to some L2 problem in your
network (due to a bug or wrong cabling) which can hit you bad in other
areas as well..
It might also be a misconfiguration (i.e. some device on that segment
uses the wrong IP address), but you can check this if you apply an
ingress access-list with "permit eigrp any any log-input" on your
FastEthernet0/0 and look at the source-mac-address of the hello packet.

	oli

> -----Original Message-----
> From: Yuval Ben-Ari [mailto:yuvalba at netvision.net.il] 
> Sent: Mittwoch, 29. Januar 2003 07:45
> To: Thomas Renzy; cisco-nsp at puck.nether.net
> Subject: RE: [nsp] IP-EIGRP: Neighbor A.B.C.D not on common subnet...
> 
> 
> I am afraid I cannot post the configs here, it will also not 
> help a lot
> for understanding the topology. (quite standard EIGRP config)
> Anyway I have a theory which I just hoped someone can confirm.
> I suspect the root for the problem is EIGRP hello packets being
> multicast and the fact that the L2 switches (Catalyst XL 
> series in this
> case) flood multicast frames on all ports including ports from other
> Vlans. In this case my only option is to ignore the messages 
> (or disable
> with "no eigrp log-neighbor-warnings")
> Can anyone confirm that ?
> 
> 	--Yuval
> 
> > -----Original Message-----
> > From: Thomas Renzy [mailto:thomas.renzy at veritas.com] 
> > Sent: Tuesday, January 28, 2003 12:02 AM
> > To: Yuval Ben-Ari; cisco-nsp at puck.nether.net
> > Subject: RE: [nsp] IP-EIGRP: Neighbor A.B.C.D not on common 
> subnet...
> > 
> > 
> > Hi,
> > 
> > I have never seen an EIGRP hello relayed from a router, nor 
> > have I ever
> > configured it. Would it be possible to see a copy of the EIGRP
> > configurations to see what is configured?
> > 
> > Thanks,
> > Thomas
> > 
> > Thomas Renzy 
> > IS&T Global Network Services
> > VERITAS Software
> > Office: +650-527-4734
> > Mobile: +650-996-7048
> > Fax: +650-527-2034
> > 
> > "Some people drink from the fountain of knowledge, others 
> > just gargle." -
> > Author Robert Anthony
> > 
> > 
> > 
> > -----Original Message-----
> > From: Yuval Ben-Ari [mailto:yuvalba at netvision.net.il]
> > Sent: Monday, January 27, 2003 7:07 AM
> > To: Thomas Renzy; cisco-nsp at puck.nether.net
> > Subject: RE: [nsp] IP-EIGRP: Neighbor A.B.C.D not on common 
> subnet...
> > 
> > 
> > Hi,
> > 
> > Not sure I understand your question,
> > the complaining router has 2 intefaces to 2 different segements.
> > the router sending the hello packet has single interface to another
> > segment (not one of the above 2).
> > all the 3 segments has a common router connected to it (core router)
> > I suspect the router is relaying the hello, is it possible ?
> > 
> > Were you able to eliminate the problem in your case ?
> > 
> > Yuval.
> > 
> > PS
> > I found this doc: http://www.cisco.com/warp/public/103/15.html
> > but it does not explain how I see the hello from a router 
> on different
> > Vlan.
> > 
> > > -----Original Message-----
> > > From: Thomas Renzy [mailto:thomas.renzy at veritas.com] 
> > > Sent: Monday, January 27, 2003 12:01 AM
> > > To: Yuval Ben-Ari; cisco-nsp at puck.nether.net
> > > Subject: RE: [nsp] IP-EIGRP: Neighbor A.B.C.D not on common 
> > subnet...
> > > 
> > > 
> > > Yuval,
> > > 
> > > Do you have an EIGRP neighbor on this segment with a 
> > > secondary interface
> > > configured? I've seen this type of message when, on an 
> > > Ethernet segment, an
> > > EIGRP neighbor has a secondary interface configured on one 
> > > router, but not
> > > on another router on the same Ethernet segment.
> > > 
> > > EIGRP hello packets have a TTL of 2, so I don't think it 
> > > traverse the next
> > > hop. 
> > > 
> > > Thanks,
> > > Thomas Renzy 
> > > IS&T Global Network Services
> > > VERITAS Software
> > > Office: +650-527-4734
> > > Mobile: +650-996-7048
> > > Fax: +650-527-2034
> > > 
> > > "Some people drink from the fountain of knowledge, others 
> > > just gargle." -
> > > Author Robert Anthony
> > > 
> > > 
> > > 
> > > -----Original Message-----
> > > From: Yuval Ben-Ari [mailto:yuvalba at netvision.net.il]
> > > Sent: Sunday, January 26, 2003 3:11 AM
> > > To: cisco-nsp at puck.nether.net
> > > Subject: [nsp] IP-EIGRP: Neighbor A.B.C.D not on common subnet...
> > > 
> > > 
> > > Hi,
> > > 
> > > I noticed messages of the above kind while logging to a router and
> > > issuing 'term mon':
> > > 
> > > Jan 26 13:01:59.566 IST: IP-EIGRP(Default-IP-Routing-Table:1680):
> > > Neighbor A.B.C.D not on common subnet for FastEthernet0/0
> > > 
> > > Obviously the message means the router is seeing EIGRP 
> hello packets
> > > coming on the interface from a neighbor which is not on that 
> > > interface's
> > > subnet, which happens to be correct.
> > > However I have no idea how these packets get to the 
> > interface as it is
> > > not on the same L2 segment (different VLAN).
> > > The error is only reported on terminal and not on all routers 
> > > (seems to
> > > be IOS dependent + 'eigrp log-neighbor-warnings' command)
> > > 
> > > Is it possible the hello packet is transiting a L3 device ?
> > > 
> > > Will be happy to hear your ideas.
> > > 
> > > Thanks.
> > > 
> > > _______________________________________________
> > > cisco-nsp mailing list  cisco-nsp at puck.nether.net
> > > http://puck.nether.net/mailman/listinfo/cisco-nsp
> > > archive at http://puck.nether.net/pipermail/cisco-nsp/
> > > 
> > 
> 
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