[c-nsp] Strange ARP problem between 3560 and Linksys

[Raymond Macharia]

Sounds like STP to me, how have you configured the STP. please privide a
simple schematic of physical connections. will help in narrowing down to the
source of your problem

Raymond Macharia

On 9/4/07, Garry Glendown <garry at glendown.de> wrote:
>
> Hi,
>
> I've had some strange problem at a customer site ... setup generally
> looks like this: two 3560 (call the A and B), connected to each other
> via 2 port etherchannel, each of the two connected via one fiber link to
> a Linksys SRW 2024 (called L). STP blocks one of the fiber links (let's
> say between B and L), everything looks good on layer 2/3 ... Multiple
> VLANs are in use, which are trunked between the Ciscos and the Linksys,
> though only 4 VLANs are actually in use on the Linksys (the others
> aren't configured).
>
> Now for the problem, I can't seem to get any ARP requests through from
> the Cisco switches to the Linksys, at least not from anything further
> than A: I can ping anything connected to L from A, though neither B nor
> other hosts hooked up to A can reach anything connected to L. I did a
> "debug arp" on A, and I do see the arp requests coming in. Once the
> boxes connected to L actively ping (or anything else) anything hooked up
> to either A or B, that destination can then reach that box as it then
> has the MAC of the box (so MAC addresses seem to be learned correctly on
> the Cisco switches). Doing a tcpdump on a Linux box hooked up to L
> showed me no ARP requests from behind A, so there must be SOMETHING
> keeping either A from forwarding the ARP requests, or L from accepting
> them on the trunk link.
>
> As the Linksys was just hooked up replacing a 3524, without any changes
> to the two 3560s, I wouldn't expect the Cisco switches to be causing
> this ... especially as there isn't much to the port config anyway...:
>
> interface GigabitEthernet0/26
> switchport trunk encapsulation dot1q
> switchport mode trunk
> speed nonegotiate
>
> Storm Control and stuff is all disabled on the Linksys, can't really see
> anything else in the config that could/should cause this kind of problem
> ...
>
> Anybody have any suggestions?
>
> Tnx!
>
> --
>
> They who would give up an essential liberty for temporary security,
> neiter deserve nor receives either   --  B.Franklin
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-- 
Raymond Macharia