Recently I have been noticing an issue with my IPv6 networking. Everything was working fine locally but if I connected from outside the network then connections would lock up when they got busy.

It took a bit of investigating but I discovered that the IPv6 MTU size wasn’t being detected correctly by some devices. The reason it would work locally was that the local network’s MTU was 1500, but for IPv6 packets leaving the network the routing goes through an IPv4 tunnel, which results in it having a lower MTU size.

The solution was to add a line to the radvd.conf file (used by the daemon that handle the router advertisements). The line that I added was

AdvLinkMTU 1280;

Which results in those devices that configure their IPv6 details from the router advertisement setting their MTU to 1280 which is the minimum datagram size for IPv6.

I have spent this morning figuring out how to get a DSpace Handle Server to accept connections over both IPv4 and IPv6. Previously it was working over IPv4 only. The usual Google hunt didn’t turn up any advice, though it did turn up the exact opposite of what I wanted (how to get it to only run on IPv4).

In the end the solution turned out to be very simple, just not documented. In the handle server’s configuration file changing the bind_address entries from the IPv4 address to :: and it will start listening on the relevant port on all interfaces (IPv4 and IPv6).