[c-nsp] Interface helper-address and Load-Balancing

[Nick Hilliard]

Saku Ytti wrote:
> Requests will be sent to all configured helper-addresses.

dhcp OFFER replies will be issued from all the configured dhcp servers
which are configured to reply.  The dhcp client will then issue a dhcp
REQUEST for one of these offers. Usually this would be the first offer
received, but there is no guarantee - it's up to the client which one
they choose.

Most dhcp servers have the capability of clustering either in
active/active or active/passive mode, so in practice the client will
either receive multiple OFFERs for the same IP address from a clustered
configuration, or else they will receive only a single offer from the
single active dhcp server.

>From the router point of view, it's a good idea to bear in mind that on
all platforms, dhcp relay causes dhcp packets in each direction to be
punted to the RP, where they are dissected, processed and forwarded
after modification.  I.e. CoPP is advisable unless you want to open up a
ddos vector on your network.

As a side note, enabling dhcp relay on any interface on vendor J
trio/trio3D platforms causes all data plane dhcp packets to be punted, oops.

Nick