6. FAQ for IPv6 routes

6.1. Support of an IPv6 default route

One idea of IPv6 was a hierachical routing, therefore only less routing entries are needed in routers.

There are some issues in current Linux kernels:

6.1.1. Clients (not routing any packet!)

Client can setup a default route like prefix “::/0”, they also learn such route on autoconfiguration e.g. using radvd on the link like following example shows:

# ip -6 route show | grep ^default
default via fe80::212:34ff:fe12:3450 dev eth0 proto kernel metric 1024 expires
¬ 29sec mtu 1500 advmss 1440

6.1.2. Routers in case of packet forwarding

Older Linux kernel (at least <= 2.4.17) don't support default routes. You can set them up, but the route lookup fails when a packet should be forwarded (normal intention of a router). If you're still using such older kernel, “default routing” can be setup using the currently used global address prefix “2000::/3”.

Note: take care about default routing without address filtering on edge routers. Otherwise unwanted multicast or site-local traffic can leave the edge.