[c-nsp] huge amount of weird traffic on poin-to-point ethernet link

Jay Hennigan jay at west.net
Thu Nov 9 19:25:21 EST 2006

Primoz Jeroncic wrote:

> Ok now my problem... Ethernet utilization on main router went up to
> 100% and when I was checking traffic with netflow I noticed huge
> amount of traffic between and There
> were only less then 30 flows in 30mins, but there were more then
> 6GB of traffic between those two addresses in this time.
> and
> Really weird thing is, that I don't route private prefixes over this
> link and none of routers (main router and L3 switches) has
> prefix (or part of it) in its routing tables. Also there's no private
> prefixes in any of my routing tables.
> Does anyone have some idea how to locate what exactly is happening?
> I don't mean for backwards, but in case if it will happen in future
> again. For now I routed to Null0 on main router and
> traffic stoped, but I still want to know what or who caused this
> weird traffic.
> PS: Just another info... traffic didn't go out on any other ports on
> main router, so it was really just on link between main router and L3
> switch.

Indeed strange.  I'd do a "sho ip arp" on those addresses, see if they 
are in any of your layer 2 devices, look up vendor codes to try to 
determine the origin.  http://coffer.com/mac_find/  is a good tool for 
this.  Maybe a peer-to-peer app trying to stream to a private IP in error?

We see a lot of weirdness with customer NAT boxes and their DHCP 
servers, but they typically cause spew 192.168.0.x or 192.168.1.x.  If 
you see someone has a Sonicwall at factory default 
plugged in wrong.

Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
NetLojix Communications, Inc.  -  http://www.netlojix.com/
WestNet:  Connecting you to the planet.  805 884-6323 - WB6RDV

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