[Gllug] Oddity in IPv6 routing

[Anthony Newman]

John Winters wrote:
> and then the rest of the machines on my LAN get global IPv6 addresses 
> with the assistance of radvd (that is, a combination of my /64 prefix 
> and their MAC addresses).

I suppose that's actually how it's supposed to work because your router 
should be handing out link-local fe80:: addresses as well to aid with 
the routing; I can't say I like it though. This is supposed to be the 
replacement for DHCPv4 as well...


> As far as I can see the two endpoint addresses of the tunnel (xxx::1 and 
>   xxx::2) never actually get used for anything, but I've yet to find a 
> way of configuring it without specifying some sort of addresses for the 
> end points.

> The only problem I can see is if one of the machines on my LAN actually 
> wanted to send a packet to one of the tunnel end-point addresses then it 
> would fail because it would think the address was local rather than on 
> the other side of the router.  I can't think why it would want to though.

My local v6 routing table at the end of a tunnel also looks like:

2001:6f8:96c:2::/64 via :: dev sit1
2000::/3 dev sit1

which appears odd at a glance because 2001:6f8:96c:2::2 is the local 
tunnel endpoint address I have assigned; of course they're on the same 
effective network segment (the tunnel) so this makes sense, and your 
local tunnel endpoint has to have an address if you want to exchange 
traffic with the local machine's network stack or the remote endpoint 
directly; it doesn't have to have one if you don't want for a v6-in-v4 
tunnel AFAICS, unless the routing table on the tunnel remote specifies a 
next hop address rather than a device for packets to be fired at; if 
your tunnel provider tells you to use an address at your end, you might 
be wise to do so :)


> I do actually have a /48 allocation and could get a second /64 routed 
> down the link if I wanted to, but as you say it seems very wasteful.

I once thought that but with 64K times as many /48s as there are IPv4 
/32s that people throw around even now it seems like just something to 
accept as the new world order :)


Ant
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