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

[Yuval Ben-Ari]

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.
> > 
> > _______________________________________________
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>