[c-nsp] Bridge devices - ARP takeover

[Rodney Dunn]

I've seen some funky things like this before, ie: with cable modems that 
  are supposed to be L1 only transparent but monkey up the stack.

If he hardcoded the mac's the adj should never change for CEF.

Verify it with 'sh adj detail' and sh ip arp.

Rodney



Jeff Fitzwater wrote:
> IF you hardcoded the ARP in both routers, then they should never 
> change.   So what exactly breaks?  Can you ping the other router? What 
> is the other routers ARP entry and visa versa?  They better be the ones 
> you put in.
> 
> 
> 
> Jeff
> On Aug 13, 2009, at 4:53 PM, Graham Wooden wrote:
> 
>> I say 30 minutes ... But I just had it occur on less than 5 minutes from
>> having the far end router and radio rebooted. And apparently my 
>> attempt to
>> hardcode the MAC addresses on both ends didn't fix it.  I am going to 
>> start
>> blaming the radios I think ...
>>
>>
>> On 8/13/09 2:55 PM, "Jeff Fitzwater" <jfitz at Princeton.EDU> wrote:
>>
>>> It's interesting to note that this occurs at about the default ARP
>>> timeout of 1800 seconds  (Is that what the router is configured
>>> for?).   That implies that when the arp times out and the router arps
>>> for the other end, it get an ARP REPLY from the wireless device.   Is
>>> that what you are saying?   This would seem to say that the wireless
>>> device may have some local proxy arp enabled so it responds to arp
>>> requests on the local net.
>>>
>>>
>>>
>>> Jeff Fitzwater
>>> OIT Network Systems
>>> Princeton University
>>> On Aug 13, 2009, at 3:08 PM, Rodney Dunn wrote:
>>>
>>>> I can't follow the problem.
>>>>
>>>> The router should try to defend the mac address it owns but if
>>>> another device simply takes over for it the only way to resolve that
>>>> is fix that device.
>>>>
>>>> How exactly is it taking over?
>>>> What is the topo (ascii diagram would work).
>>>>
>>>> Rodney
>>>>
>>>>
>>>>
>>>> Graham Wooden wrote:
>>>>> Hi there,
>>>>> I have a customer hanging off of my edge router (6509/
>>>>> Sup32/12.2.33SXI), doing a Point-to-Point wireless shot from the DC
>>>>> to another site.
>>>>> On myside, it's a L3 VLAN doing a /30 to a smaller Cisco router on
>>>>> the other end. I am then statically routing some additional subnets
>>>>> to the far end router.
>>>>> After about 30 minutes of the link being powered up, the MAC
>>>>> address of local Radio appears to take over the /30, and hence all
>>>>> routing breaks.  To fix this, seems to that if I hardcode the MAC
>>>>> that belongs to the Cisco router on the far, all seems good and
>>>>> traffic keeps on trucking. The other fix that was being done until
>>>>> the hardcode went into affect, was power cycling the local radio.
>>>>> My question is this:  While the hardcoding seems to be the trick to
>>>>> solve this, is there another command, maybe on the interface to
>>>>> achieve this fix too?
>>>>> I have yet to find out from the customer if there are any MAC/ARP
>>>>> settings in his radios and that could be doing take over on purpose.
>>>>> I am hoping that I can curb this type of behaviour without getting
>>>>> him involved.
>>>>> Thoughts to this?  Thanks,
>>>>> -graham
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