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I need to create a router that will make ipv6 available to downstream users if it is available.

I have encountered two problems using the "naive" approach:

1) I am receiving a /64 address from upstream via radvd. When I turn radvd on on the router, the network becomes unreachable. (I'm also not sure what address to specify.)

2) In general, given the fact that there may be multiple routers on the same network, I'm not sure what kind of address to specify in order to ensure uniqueness down the line.

I'm doing this all in Debian (actually, the pilot version is in Etch for reasons we need not go into).

Thanks!

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Are you sure you need a router? If someone is already managing addresses, would not a bridging firewall be enough for your purpose? –  Bittrance Apr 26 '11 at 6:46

1 Answer 1

You cannot (normally) be autoconfigured and be a router at the same time. One of them will have to drop, and that is why your network becomes unreachable.

/64 is the prefix that you assign to datalink-layer network segments. Someone runs radvd to put your machine in a /64 prefix. You cannot run radvd on such address to give more addresses to other machines, because you would be stealing the domain of the radvd above you.

End users are supposed to have /48 prefixes (sometimes /56), where you can partition your network in up to 65536 /64 prefixes, and you run radvd to serve these prefixes.

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Ouch. That makes great sense. Unfortunately, I find myself in a situation where I have to be able to provide IPv6 in a situation where it is available to the router. Would using dhcp6 have a snowball's chance of working in this environment? –  Artie Gold Feb 16 '11 at 23:53
    
@Artie No, because DHCPv6 would still be stealing from the prefix which is controlled by the radvd above you. If you have an autoconfigured /64, you should put all machines in the same network using switches. –  Juliano Feb 17 '11 at 2:30

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