IP-Helper

[Oron Yaniv]

Hi All,

i am asking my self how IP-helper work?

how IP helper differentiate between services?

for example, when a packet of DHCP request riching the helper, base on which packet`s field the helper deciding that this packet is DHCP? (base on ports/UDP, Payload or Layer 2 B.C etc.) 

Thanks,

Oron Yaniv

[luis_cordova · Accepted solution]

Hi @Oron Yaniv,

The DHCP discover packets are identified by the port number associated with the DHCP service (UDP: source port = 68; destination port = 67).

These packets are sent with the broadcast destination address, but if a DHCP server is not found in the local network, the ip helper-address command changes the destination ip broadcast by a unicast destination ip (the one you indicate after the command ).
With this, it is possible for the packet to reach a DHCP server outside the broadcast domain.

Regards