[c-nsp] 7507 and 5500 arp oddities

[Rodney Dunn]

You are somewhat misusing some terms.

You say "lose routes" but you are talking about directly
connected subnets and arp. When we say "lose routes" it means
they are gone from the routing table (sh ip route). When
you lose arp's they are gone in 'sh ip arp'.

You say "suddenly become lost". I don't know how to extract
what you mean. You can't ping them from the router?

Bottom line, sniffer is your friend.

Regardless of what is in the MPLS core (I've seen hundreds
of 75xx's with dual FE OSPF uplinks to a GSR core) if
you can't reach the machines from the 75xx down the etherchannel
it's most likely a L2 type issue between the host and the 75xx.

To forward packets from the 75xx you need:
a route (should be directly connected)
an arp (sh ip arp)
a CEF adjacency (sh adj detail) (Are you running dCEF? What code?)

Those are the minimum things you have to start looking at.

As for the L2 stuff such as spanning tree, someone else will have
to help ya.

Rodney



On Thu, Jun 30, 2005 at 11:17:04AM -0500, James Saker wrote:
> I have a "works in the lab but not in the field" issue with a 7507
> etherchannel'ed out to a Catalyst 5500 with VLANs to each 5500 port for
> router port control. Under production traffic load (2-5 Mbps), the 7507
> begins losing arp representations of the remote systems. Arp associations
> even with direct-connected systems take 5+ minutes. 
> 
> As the same topology works fine with a Cisco 2651 connected to a (gasp)
> Catalyst 2800 switch, I'm wondering if I've either got an arp issue or if my
> ugly "eight /30 links on a single VLAN, single port" legacy design is
> confusing the 7507/5500. Or perhaps there's some 7507/5500 tuning magic I've
> overlooked somewhere.
> 
> A high level of the design is:
> 
> Upstream 7507-->MPLS Core
> 
> MPLS Core-(dual OSPF Ethernet links)-->7507
> 
> 7507--(dual 100BASET Etherchannel, VLAN trunk)-->5500
> 
> 5500-(unique VLAN per port, e.g. VLAN 707 for interface 7/07)-> remotes
> 
> On one local VLAN, I have a /29 network for connecting tech laptops. Today
> it took more than 5 minutes to have ARP associate me with the 7507. I could
> immediately ping laptop to laptop on the LAN, but the 5500 and 7507 wouldn't
> let me past. ARP table on 7507 actually had an entry for me though, but no
> ping/reply and no routing past 7507.
> 
> Interestingly, the 5500 has suddenly become lost to the 7507 in the
> management VLAN talking to sc0 - worked fine in lab. No changes in config,
> but now it refuses to talk. There are no other VLANs connected to this
> switch (VLAN only used to fan out from 7500), so it's not as if I'm
> encountering another VLAN out there competing for control.
> 
> Another intrigue is that the 7507 lost some but not all of my remotes on one
> VLAN/port, VLAN 709 (catalyst 7/09) had eight /30 links via a
> point-multipoint radio system; e.g. 10.1.1.0/30 goes to one remote 2650
> router over a multipoint radio system. The 7507/5500 is connected to an
> access point here, and each remote radio talks to a 2650 router. Three of
> these routers got lost overnight, while the rest of the /30 subnets were
> still visible to the 7507. Getting into the radios, all was happy - for some
> reason, the 7507/5500 seems to be losing these connected routes. Naturally,
> in the lab it all worked fine for two months and I never saw this behavior.
> Any thoughts are greatly appreciated!
> 
> Jamie
> 
> 
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