Opened 5 years ago

Last modified 5 years ago

#13275 assigned defect

Chaining 6relayd fragments the network

Reported by: Paul Marks <paul@…> Owned by: cyrus
Priority: normal Milestone: Chaos Calmer 15.05
Component: packages Version: Trunk
Keywords: Cc:


I currently run a LAN based on odhcp6c and 6relayd, and it works great.

The LAN uses the and 2601:9:4600:3b::/64 subnets. As an experiment, I connected a second OpenWRT router to the network using WiFi in STA mode.

IPv4 works fine beause it's NATted to the subnet, and IPv6 *almost* works. The clients share the same /64 as the primary network thanks to 6relayd, and are able to reach the Internet, scoring 10/10 on

The problem is, 6relayd is asymmetric. Hosts behind the second router are unable to reach hosts on my primary network, unless I configure static routes for them. This is especially problematic because the second 6relayd automatically advertises "2601:9:4600:3b::1" as a DNS resolver.

I know that I could use WDS, or assign another /64 to the second network (if Comcast allowed shorter prefixes). But for the sake of argument, let's pretend the primary LAN is operated by my ISP, and I have no control over its settings. With IPv4, I can extend the network using NAT, but with IPv6, NAT is Evil™.

I think the concept of 6relayd is awesome, because it gives any user the power to extend a network without cooperation from the ISP. So are there plans to fix the subnet fragmentation problem by implementing the rest of RFC4389?

At the very least, 6relayd shouldn't advertise a DNS resolver that it knows will be unreachable.

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Change History (2)

comment:1 Changed 5 years ago by cyrus

  • Owner changed from developers to cyrus
  • Status changed from new to assigned

Thanks for the report. I'll look into it.

comment:2 Changed 5 years ago by cyrus

Some more comments: Usually the routes for individual host on both sides should be set automatically and it worked at some point, maybe there is something wrong with that feature. I haven't tested it for a few months.

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