[c-nsp] Bridge devices - ARP takeover

[Jeff Fitzwater]

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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>
>