ARP weirdness.

Ken D'Ambrosio ken at jots.org
Fri Nov 10 19:04:04 EST 2017


I'm guessing it was some sort of broadcast storm.  Though a very 
confusing one -- if I unplugged the cable, it stopped.  Plug it back in, 
and lo!  Starts again.  However, I finally gave up trying to supply the 
VLAN to the Linux box by way of a trunk, and just plugged the 
(still-tagged) interfaface straight in... and all was fine.  So I guess 
I don't care (the box has, like, a zillion interfaces), but I'm still 
pretty darn confused by it.

-Ken

On 2017-11-10 18:48, Ben Scott wrote:
> On Wed, Nov 8, 2017 at 4:49 PM, Ken D'Ambrosio <ken at jots.org> wrote:
>> Ubuntu box acting as a router for some subnets.
>> 
>> [192.168.200.12] <-1302 VLAN->[switch]<-1302 VLAN->switch<-1302 VLAN->
>> [router @ 192.168.200.1]
> 
> So, to clarify, the Ubuntu box is at .1?  What is .12?
> 
> Can you give a concise description of what else is on the VLAN?
> 
>> The link is getting utterly spammed with ARP requests for
>> 192.168.200.12.
> 
> How are you determining this?  Packet sniffer?  If so, where?
> 
> Are these ARP requests originating from the .1 box?  You have verified
> this by MAC address of the sending system?  If you unplug .1 to test,
> does the flood stop?
> 
> One thought that immediately occurs to me is a broadcast loop.  Any
> chance of a physical loop (e.g., cable plugged into two switch ports
> on the same VLAN)?  Are you running spanning tree any/everywhere?
> 
> What are the switches?  Any particular config applied to the VLANs,
> beyond the VLAN itself?  Any weird config applied to the switch in
> general?
> 
> -- Ben
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