DHCP broadcasts

[kapishmohole.cisco]

Hello,

To allow DHCP broadcasts 'ip helper-add' command will first convert DHCP broadcast request packet coming on interface to unicast packet and then it will route that according to routing table.

For converting broadcast to unicast - router uses IP add of its own client side interface as source address and IP address of server as destination.

Similarly answer to this request from server is unicast packet it will come to DHCP client interface and then will be converted again it to broadcast to get out from DHCP client interface.

IS THIS RIGHT?

[ziutek]

Pretty much right.

Although the ip helper-add can also specify an broadcast address, not necessarily a unicast one. for example you may have all your servers, DHCP, WINS, etc. on one subnet, and want all broadcast forwarded to that subnet, and then the appropraite server accept the broadcast and respond accordingly.

DHCP responses are unicast and remain that way all the way back to the client requesting the ip address.

At least this is the way I think it works.

Regards,

Joe