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DHCP relay agents, helper address, and Option 82…
All, Between the DocCD and previous posts I’m a little bit confused regarding how DHCP works with remote DHCP servers… From what I understand…
If you have a router acting as a relay agent (i.e. there is no DHCP server local to the LAN), you configure a ‘helper address’ that points to the real DHCP server under the LAN interface you want to provide DHCP services to (basically for the relay agent router to forward all DHCP messages to). Where I start to get confused is when the documentation starts talking about the giAddr field and what that is set to? Also when do you need to use Option 82 and configure classes? And when you configure your helper addresses, can they be any IP address on the DHCP server (e.g. a loopback that is in your routing table)?
As an example: If Router A is acting as a relay agent for two directly connected LAN segments (we’ll call them Ethernet0/0 and Ethernet0/1) and relaying to Router B (who is acting as the DHCP server) how does Router B figure out which pools to map the two different LAN segments on Router A to?
ASCII Visio: E0/0 and E0/1 on RouterA RouterB (acting as DHCP server)
From previous posts… Hello,
Basically, DHCP server consults either incoming interface or “giaddr” field (relay agent IP) in DHCP packet.
HTH Petr
Tony Paterra apaterra@gmail.com
