DHCPv6 PD & Routing Questions

Thu Nov 26 10:07:35 UTC 2015

Mark Andrews <marka at isc.org> writes:

> The DHCP server usually is sitting
> in a data center on the other side of the country with zero ability
> to inject approptiate routes.

Not too sure about that.  At least, that's not what we do.  We run the
DHCPv6 and DHCP servers on our BNGs (or BRAS or whatever the current
buzzword for "access router" is).  So the "servers" have full control
of both DHCP/DHCPv6 and routing.

The DHCP backend database may need to be centralised, but tunneling the
DHCP protocol all they way through your network just to achieve that
seems unnecessarily risky and error-prone.  Moving the DHCP frontends as
close as possible to the clients is a very simple way to make DHCP
scalable and robust. If you feel you should have a DHCP server in more
than one site for robustness, then you might as well do a fully
distributed design.  Going half-way, centralising everything and then
dividing it on multiple datasenters is just ten times the trouble..

If you only do pool-based arbitrary address allocations, then you might
not need a centralised database at all.  Distribute your prefixes to the
BNGs and let them manage the pools independently of each other.

> The DHCP relay could also have injected routes but that is a second
> class solution.

DHCP relays *are* second class solutions :)  Unfortunately they cannot
always be avoided in the semi-L2-environments like ISP access networks
often are.

Bjørn