[AusNOG] Not quite routing issue

[Roland Dobbins]

On Sep 22, 2014, at 2:39 PM, Matthew Moyle-Croft <mmc at mmc.com.au> wrote:

> Unsure, but maybe it's going via some transparent proxy? 

Definitely something to try.

Look at DNS responses to the endpoint resolvers located on those netblocks/access LANs.  

Look at ACLs, QoS, PBR, etc.

If this was a recently-allocated netblock, it could be outdated bogon filters (which don't have much utility beyond reserved addresses, anymore).

Also, there might be some 'GeoIP' nonsense at play, as well.  Check with Maxmind, et. al. to see if the netblock is shown as being allocated in your region.

Finally, and most importantly, check the entire relevant layer-2 path within your span of administrative control for any port errors, cabling issues, autonegotiation mismatches, etc.  Ensure the DNS replies to the machines on that subnet aren't being mangled in transit or simply not reaching them, or only reaching them intermittently.

----------------------------------------------------------------------
Roland Dobbins <rdobbins at arbor.net> // <http://www.arbornetworks.com>

                   Equo ne credite, Teucri.

    		   	  -- Laocoön