Hi all, (Since how to run stateless DHCPv6 in 6rd scenario is also related to DHC WG, I copy this email to DHC WG mailing-list).
There are two options now for running DHCPv6 in 6rd scenario: 1) The CPE as a DHCP relay agent sends the DHCP-relay-forward message to ALL-DHCP-SERVER/RELAY multicast address. The only available way of forwarding multicast in 6rd is to tunnel this multicast DHCP message to the BR which acts as a DHCP server/relay. If a 6rd SP deployed multiple BRs for load-balancing (by using anycast), each BR should be enabled as a DHCP server or a DHCP relay agent. 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 wonder whether this option is acceptable from the perspective of DHCP redundancy requirement. 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. In comparison with the first option, this option has no special limitation. Of course, the CPE needs to learn the DHCPv6 server addresses through a new DHCPv4 option. For more details, please see draft-guo-softwire-6rd-ipv6-config-00. Best wishes, Xiaohu > -----邮件原件----- > 发件人: Xu Xiaohu [mailto:[email protected]] > 发送时间: 2010年8月3日 16:59 > 收件人: 'Ole Troan' > 抄送: '[email protected]' > 主题: re: [Softwires] About draft-guo-softwire-6rd-ipv6-config-00 > > Hi Ole, > > > -----邮件原件----- > > 发件人: Ole Troan [mailto:[email protected]] 代表 Ole Troan > > 发送时间: 2010年8月2日 19:17 > > 收件人: xuxiaohu 41208 > > 抄送: [email protected] > > 主题: Re: [Softwires] About draft-guo-softwire-6rd-ipv6-config-00 > > > > Xiaohu, > > > > > First, as stated in the DHCPv6 specification [RFC3315], "...The client MUST > > use a link-local address assigned to the interface for which it is requesting > > configuration information as the source address in the header of the IP > > datagram." Since the link-local address can not travel through the 6rd domain, > > the CPE SHOULD act as a DHCPv6 relay agent. I think nobody will argue against > > this conclusion. > > > > do you only need "stateless" DHCPv6? > > if so, I think the DHCPv6 specifications should loosen up on the restrictions > > of which source and destinations can be used. then you can just use a global > > address as a source and the IPv6 address of the BR as the relay/server. (I > > believe this was Townsley's proposal via IM during the softwires meeting). > > If the CPE could work as a DHCP relay agent which sends DHCP-relay-forward > messages with its global IPv6 address being the source address, the DHCPv6 > specification doesn't need any change. > > > > Second, as I mentioned during the presentation, relaying DHCP request > > messages to All_DHCP_Servers multicast address by CPEs is not optimal in 6rd > > scenario. Note that here what I said is "not optimal", rather than "not > > possible". The CPE as a relay agent, could be upgraded to relay > > information-request DHCPv6 messages (multicast) towards the 6rd BRs. > However, > > with this approach, the DHCPv6 servers would have to be located in the IPv6 > > Interne > > > t, rather than in a 6rd site which is owned by the 6rd SP. In addition, > this > > usage will result in more traffic burden on the 6rd BRs. > > > > I don't quite see that this has to be the case. the DHCPv6 server can obviously > > also be part of the SP's network. it is just placed on an "IPv6 leg" of the > > BR or the BR acts as the DHCPv6 server. the multicast packets could very well > > be encapsulated in unicast L2 (IPv4) to the BR. > > Yes, it works. However, it's not optimal. First, if a SP deployed multiple BRs > for load-balancing, each BR should be enabled as a DHCP server or a DHCP relay > agent. Second, in case that the DHCP server/relay on a given BR is unavailable > due to some reason but the other functions of it (e.g., the anycast route for > it) are still available, once the DHCP message is encapsulated in unicast L2 > (IPv4) 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. > > > > > > > Hence, we propose that the CPE as a DHCP relay agent, SHOULD know at least > > one DHCPv6 server address. > > > > of course, the other option is to just have a DNS proxy on the CPE. > > Yes, in case that DNS is the only configuration information needed. > > > in any case I would like to see these requirements in the next phase of the > > requirements for IPv6 routers in v6ops. and I'd like to start a discussion > in > > DHC about this as well as some other clarifications needed for CPE routers. > > Good idea. > > Best wishes, > Xiaohu _______________________________________________ Softwires mailing list [email protected] https://www.ietf.org/mailman/listinfo/softwires
