Matching a DHCPv6 client against its link-local address

Benjamin Cama benjamin.cama at
Sat Jun 25 10:09:25 UTC 2011


[second try, this time after subscribing to the list…]

I'm trying to set up a DHCPv6 server for a small ISP here in France, so
that we can provide, among other options, automatic prefix delegation.
My goal is to use ISC DHCP as a stateless DHCPv6 server, but I
stumbled on a first problem, independent of the “statefullness”.

Our subscribers reach us through PPP (on ADSL connections, BTW), which
come to us in the form of a L2TP tunnel. So, we don't have link-layer
addresses to match them against. Still, we _need_ to match them as we
have attributed specific IPv6 prefixes for them. One identifier we could
match against is the link-local address they use : l2tpns (our L2TP
server) build them in a particular way, embedding their IPv4 address.
But I didn't find a way to match against the link-local address the
DHCPv6 message came from. Any idea anyone ?

I think many people will say we could configure the DHCPv6 client to do
this and that, but we don't have control over them, and the point is for
the subscriber not to have to touch anything. Currently, those who want
IPv6 connectivity configure their prefix manually. Doing so for another
identifier defeats the purpose of “automatically” delegating them their

Next problem will be to interface ISC DHCP with our RADIUS server, but
this is another story.

Thanks in advance,

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