Running DHCPv6 relay without interfaces

Neff, Glen glen.neff at
Thu Mar 14 15:35:28 UTC 2013

> >> Can I able to run DHCPv6 relay with single interface
> > This makes no sense.  If you don't have multiple interfaces, then you
> > shouldn't need a relay.
>     I think it makes sense for IPv6, which uses multicast instead of the
> traditional broadcast/unicast.
>     Clients send to the link-local DHCP address "FF02::1:2". The DHCP
> server listens at the site-wide DHCP address "FF05::1:3". Something has
> to piece the two together.
>     Even in an IPv4 world, a DHCP relay does not HAVE to run on the gateway
> so a single interface relay to pick up the broadcasts and unicast them off
> the local network to the server is perfectly valid. The OP said his box had
> a single interface, not that he only had a single broadcast domain.

Since I've become the list whipping-boy for the day. . . 

While correct that a DHCPv6-relay does not have to be a router, I do not think it's correct to say a single interface can mean multiple broadcast domains.  If there was multiple broadcast domains associated with a single NIC, then surely this would be a trunked interface with sub-interfaces for each broadcast domain.

I've also struggled with both the lack of DHCPv6-relay support on Cisco NXOS devices, and 'dhcrelay -6' and its upper & lower interface designations used for ISC-DHCPv6-relay.  I'm not sure how well a config where the same interface is specified as both lower & upper would work.


 * Glen R. J. Neff
 * USD Lab Operations Infrastructure Team
 * glen.neff at
 * EMC^2 == E^2

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