Re: [Softwires] [dhcwg] Is tunnelling DHCP multicast messages in 6rd unicast tunnel to BR acceptable for DHCP redundancy?//re: About draft-guo-softwire-6rd-ipv6-config-00

[Ted Lemon <[e-mail]>]

On Aug 8, 2010, at 11:59 PM, Xu Xiaohu wrote:
> In addition, in case that the DHCP
> server/relay on a given BR is unavailable due to some reason (e.g., no
> available address in the pool) but the other functions of it (e.g., the
> anycast route for it) are still available, once the DHCP message is tunneled
> to that BR, the DHCP service is unavailable any more. That's to say, it's
> hard to achieve the high availability for DHCP servers/relay agents since
> the DHCP information-request can not be relayed to other DHCP
> servers/relays.

I don't see the problem here.   If you want redundancy, you should configure each BR to relay to more than one DHCP server.   This would be the default anyway, according to RFC3315 section 20, which requires the relay to multicast if not otherwise configured.

> 2) The CPE as a DHCP relay agent sends the DHCP-relay-forward message to one
> of the learnt DHCP server (unicast) addresses. Since 6rd can support unicast
> flexible, the DHCP server can be located either on/behind any BR or behind a
> 6rd CPE which is owned by the 6rd SP.

This is completely contrary to the recommendations in RFC3315, which require the client to multicast, and require any relays to multicast by default.   Trying to relay DHCPv6 traffic over an IPv4 transport seems needlessly complicated.   You have the tunnel--why not use it?