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On a Linux machine connected to the ipv6 internet via a router's radvd-advertised tunnel, ip -6 route accumulates recent addresses. Why does this happen? Is it expected behavior, or is the machine misconfigured? On a different machine that is connected to an ipv6 tunnel directly, ip -6 route keeps a shorter list.

On the client (which is accumulating recent addresses as routes):

ip -6 route # after pinging ipv6.google.com and www.kame.net

2001:200:dff:fff1:216:3eff:feb1:44d7 via fe80::216:1ff:fe14:444 dev eth0  proto static  metric 1024 
2001:470:8:e7c::/64 dev eth0  proto kernel  metric 256  expires 86407sec
2607:f8b0:4002:801::1011 via fe80::216:1ff:fe14:444 dev eth0  proto static  metric 1024 
fe80::/64 dev eth0  proto kernel  metric 256 
default via fe80::216:1ff:fe14:444 dev eth0  proto kernel  metric 1024 

On the router:

    ip -6 route
    ::/96 via :: dev tun6to4  metric 256  mtu 1280 advmss 1220
    2001:470:7:e7c::/64 via :: dev he-ipv6  metric 256  mtu 1480 advmss 1420
    2001:470:8:e7c::/64 dev br0  metric 256  mtu 1500 advmss 1440
    2002:62b4:2270:1::/64 dev br0  metric 256  mtu 1500 advmss 1440
    2002::/16 dev tun6to4  metric 256  mtu 1280 advmss 1220
    2000::/3 dev he-ipv6  metric 1024  mtu 1480 advmss 1420
    fe80::/64 dev eth0  metric 256  mtu 1500 advmss 1440
    fe80::/64 dev vlan0  metric 256  mtu 1500 advmss 1440
    fe80::/64 dev eth1  metric 256  mtu 1500 advmss 1440
    fe80::/64 dev br0  metric 256  mtu 1500 advmss 1440
    fe80::/64 dev vlan1  metric 256  mtu 1500 advmss 1440
    fe80::/64 via :: dev he-ipv6  metric 256  mtu 1480 advmss 1420
    fe80::/64 dev tun6to4  metric 256  mtu 1280 advmss 1220
    ff00::/8 dev eth0  metric 256  mtu 1500 advmss 1440
    ff00::/8 dev vlan0  metric 256  mtu 1500 advmss 1440
    ff00::/8 dev eth1  metric 256  mtu 1500 advmss 1440
    ff00::/8 dev br0  metric 256  mtu 1500 advmss 1440
    ff00::/8 dev vlan1  metric 256  mtu 1500 advmss 1440
    ff00::/8 dev he-ipv6  metric 256  mtu 1480 advmss 1420
    ff00::/8 dev tun6to4  metric 256  mtu 1280 advmss 1220
    default dev he-ipv6  metric 1024  mtu 1480 advmss 1420

ip -6 a
1: lo: <LOOPBACK,MULTICAST,UP>
    inet6 ::1/128 scope host
3: eth0: <BROADCAST,MULTICAST,PROMISC,UP>
    inet6 fe80::216:1ff:fe14:444/64 scope link
4: eth1: <BROADCAST,MULTICAST,PROMISC,UP>
    inet6 fe80::216:1ff:fe14:446/64 scope link
5: vlan0: <BROADCAST,MULTICAST,PROMISC,UP>
    inet6 fe80::216:1ff:fe14:444/64 scope link
6: vlan1: <BROADCAST,MULTICAST,UP>
    inet6 fe80::216:1ff:fe14:445/64 scope link
8: br0: <BROADCAST,MULTICAST,PROMISC,UP>
    inet6 fe80::216:1ff:fe14:444/64 scope link
    inet6 2002:62b4:2270:1::1/64 scope global
    inet6 2001:470:8:e7c::1/64 scope global
12: he-ipv6: <POINTOPOINT,NOARP,UP>
    inet6 2001:470:7:e7c::2/64 scope global
    inet6 fe80::62b4:2270/128 scope link
13: tun6to4: <NOARP,UP>
    inet6 2002:62b4:2270::1/16 scope global
    inet6 ::98.180.34.112/128 scope global

radvd.conf:

interface br0 {
AdvSendAdvert on;
prefix 2001:470:8:e7c::/64 {
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr off;
};
};
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Can you show some more routes, and also the output of ip -6 addr? –  Sander Steffann Apr 25 '12 at 3:28
    
@SanderSteffann there's the info. –  joeforker Apr 26 '12 at 20:33
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1 Answer

I suspect what is happening here is that the router doesn't have an address in the 2001:888:0:18:: range, so the router is broadcasting its route advertisements using its link-local address (fe80::444).

Since the fe80:: range isn't associated with a particular interface the client machine needs to track which interface to use when sending packets to fe80::444, so it adds an entry to its routing table.

If your router picks up an address on the same network, say 2001:888:0:18::1, I suspect this behaviour might change.

share|improve this answer
    
That sounds promising. radvd is specifically configured with the link-local address, in an attempt to only advertise on the LAN. I can change that and see what happens. –  joeforker Apr 25 '12 at 15:53
    
You can do this by advertising on the LAN interface only rather than on a link-local address. –  dwurf Apr 25 '12 at 21:59
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