[c-nsp] Setting relay agent IP on 4500

[Phil Mayers]

On 29/07/17 13:43, Nathan Lannine wrote:
>>> The issue is the 4500 stamps the relay agent IP in the DISCOVER as
>>> being the incoming interface IP where the DISCOVER was received,
>
> Yeah, that's expected and required behavior.  I sort of assumed, as
> Mr. Mayer indicated, that the "global" option would still set the
> giaddr to the receiving vrf gateway address, but set the source to
> some address in the global table.  It never occurred to me that a dhcp
> server would not support this behavior.

By default, DHCP servers reply to the giaddr as opposed to source IP 
because there may have been intermediate DHCP relays (you can chain 
them, hence the "hops" field)

I haven't checked the source but the docs for Kea make it sound vaguely 
as if this might be an option that helps in this setup:

http://kea.isc.org/docs/kea-guide.html#dhcp4-relay-override

>
> We accomplish this with intervrf routing and leave out the "global"
> option, which keeps the discovers/requests in the vrf and sourced from
> the vrf gateway address.

This is what we do.

There is also the option of a "services" VRF and using route 
import/export to the customer VRFs.