RE: [dhcwg] Feedback on Layer 2 Relay Agent functionality

[David Miles <davidm at thetiger.com>]

With the recent discussions around Layer 2 Relay Agents (such as that  
described in DSL Forum TR-101 Appendix B) has there been consideration  
of the equivalent for IPv6?

Today Layer 2 Relay Agents are an integral part of TR-101 when N:1  
VLANs are used. As we move towards IPv6 deployments there is a desire  
to keep the fundamental layer 2 architecture (N:1) which suggests a  
similar function for DHCPv6 in the DSLAM.
Like the current DSL Forum L2 DHCPv4 Relay Agent, the purpose for the  
relay agent is to add DHCPv6 Remote ID (equivalent to DHCPv4 Option  
82) so that a server can determine policy based on value matching.

In DHCPv6 things become more challenging as for starters there is no  
real "layer 2". There seem to be two general options:

1) Implement a DHCPv6 Relay on the DSLAM
	- Implication is that the DSLAM must then have a IPv6 address (link- 
local) and stack, participating as an actual node in the N:1 VLAN (ie,  
the DSLAM should perform DAD and possibly ND)
	- As the DSLAM does not act as an IPv6 router, the Relay-Forward link  
address would be unspecified and thus requires the addition of  
Interface ID
	- The interface ID itself could then be used to convey the "circuit"  
to the router

2) DSLAM inserts Option 37 (Remote ID) into DHCPv6 messages
	- Inserts information into a client-sourced Solicit without the  
client knowledge
	- Minimal impact on the DSLAM (no need for complete IPv6 stack
	- Not supported by DHCPv6 (RFC 3315) as Option 37 is a Relay Agent  
Option

I wouldn't suggest the above satisfactorily explores the issues  
relating to DHCPv6 Relay Agents in a DSLAM, but hopefully it may stir  
some ideas. IPv6 deployments are just on the horizon for carriers but  
without clear directives we could see multiple (and incompatible)  
approaches.

My apologies if this has been discussed prior (I couldn't find any  
direct references in the archives)


Regards,

- David

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