dhcp v4 server bypassing relay agent ip addr and directly replying to ciaddr

[Matthew Newton]

On Wed, 2019-03-20 at 07:46 +0000, Katuri, Vikram wrote:
> Discover from my client targeted at the relay is making its way to
> the dhcp server , but the offer packet from the server is bypassing
> the relay and directly landing onto the client.
>        
> from the pcap it appears that the server (v4) is stripping off the
> ciaddr and giaddr in the offer packer.
> 
> (0)  running request
> (0)  Received DHCP-Discover XID 00000000 from 10.43.18.35:67 to
> 10.43.18.95:67 via eth1 
> (0)    &DHCP-Opcode = Client-Message
> (0)    &DHCP-Hardware-Type = Ethernet
...
> (0)    &DHCP-Gateway-IP-Address = 10.43.18.35

Copy the giaddr from the incoming request to the reply:

> (0)    update reply {
> (0)      &DHCP-Domain-Name-Server = 127.0.0.1
> (0)      &DHCP-Domain-Name-Server = 127.0.0.2
> (0)      &DHCP-Subnet-Mask = 255.255.255.0
> (0)      &DHCP-Router-Address = 192.0.2.1
> (0)      &DHCP-IP-Address-Lease-Time = 900
> (0)      &DHCP-DHCP-Server-Identifier = 192.0.2.1
> (0)    } # update reply (noop)

Add

&DHCP-Gateway-IP-Address := &request:DHCP-Gateway-IP-Address

-- 
Matthew