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November 28, 2012

Working Around the HE/Cogent IPv6 Peering Dispute

I was recently affected by the long-standing IPv6 peering dispute between Hurricane Electric and Cogent. On one of my systems which uses Hurricane Electric's IPv6 tunnel broker, connections to dual-homed hosts on Cogent's network were taking unreasonable amounts of time to establish, as attempts to use IPv6 had to time out before IPv4 was tried. Reverse DNS lookups on Cogent IP address space were taking 10 seconds to time out, causing frustrating delays for incoming ssh users, even over IPv4. Before you go blaming the tunnel, you should know that I observed the same problems from a server in a Hurricane Electric data center with native IPv6.

I've long been a fan of using reject routes to force faster failover when faced with less-than-ideal network conditions, so I turned to them again to work around this issue. I knew that if I added reject routes to Cogent's IPv6 address space, applications would immediately fail over to IPv4 without needing to first time out on IPv6.

First, I used Hurricane Electric's handy BGP Tookit to look up the IPv6 prefixes announced by AS174. AS174 is Cogent's autonomous system number. Conveniently, it was printed on Hurricane Electric's cake, saving me the trouble of looking it up.

Then, I wrote a script to add reject routes to these prefixes:

#!/bin/sh for prefix in 2001:0550::/32 2001:067c:12e8::/48 2001:0978::/32 2607:9700::/32 2607:f298:000a::/48 2607:f5d8::/32 2610:00f8:2f00::/48 2610:00f8:2fed::/48 2620:009a:8000::/48 2620:00fb::/48 2620:00fb::/56 do ip -6 route add unreachable $prefix 2>/dev/null done exit 0

I stuck this in a system start up script so it's run every time the system boots.

This solves the problem, in the sense that there is no longer a long delay when accessing dual-homed Cogent hosts. Of course, it precludes the use of IPv6, which would be a problem if I needed to contact an IPv6-only Cogent host. Fortunately, hosts will be either dual-homed or IPv4-only for the foreseeable future. Still, I'm appalled that even after the World IPv6 Launch, two major transit providers are locked in such a lengthy IPv6 peering dispute.


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