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How do you configure DHCP relay from one subnet to another?

Verfasst: Fr 17.07.2009, 12:25
von ajl119
Hello,

Is it possible to enable DHCP relaying from one subnet to another through Securepoint?

Thank you, Andy.

How do you configure DHCP relay from one subnet to another?

Verfasst: Fr 17.07.2009, 13:16
von carsten

How do you configure DHCP relay from one subnet to another?

Verfasst: Fr 24.07.2009, 15:03
von ajl119
Hello,
Thanks for this. I think dhcrelay is ok.

The DHCP servers are located on our LAN (eth7).
We want DHCP broadcasts originating in dmz1 (eth4), to be forwarded to the LAN DHCP servers.

'/usr/sbin/dhcrelay -q -i eth4 -m forward 192.168.200.1 192.168.200.2'

However, the broadcast packets are being dropped at the securepoints dmz1 interface.

I created two network objects;
255.255.255.255/32 in zone 'firewall-dmz1' = 'DMZ1_Interface'
0.0.0.0/0 in zone 'dmz1' = 'DMZ1_any'

I created a service group with one service object;
Name: 'DHCPRelay', protocol: UDP, Source: 67:68, Destination: 67:68

I then created a firewall rule;
From: DMZ_any, To: DMZ_Interface, Service: DHCPRelay

However the logs show my DHCP broadcasts are being dropped!!!

Log;
'Firewall DROP' IN=eth4 OUT= MAC=ff:ff:ff:ff:ff:ff:00:0c:29:80:5d:b0:08:00 SRC=0.0.0.0 DST=255.255.255.255 LEN=328 TOS=0x00 PREC=0x00 TTL=128 ID=16 PROTO=UDP SPT=68 DPT=67 LEN=308

How do you configure DHCP relay from one subnet to another?

Verfasst: Sa 25.07.2009, 12:20
von Erik
Hi,
if the zones on eth4 equal "dmz1;firewall-dmz1" I don't see any reason, why the (DHCP Request) packets are dropped.
For letting the DHCP Reply packets pass through the firewall, you need to create a rule:
[Your DHCP-Server](internal) -> 255.255.255.255/32(internal-interface) -> dhcp-relay

To ensure, that the rules are correctly written to iptables execute the following command in a root-shell:

Code: Alles auswählen

# iptables -L INPUT -t filter -n -v | grep "67:68"
The output should read similar to the following:

Code: Alles auswählen

   82 26896 ACCEPT_LOG_ALL_8  udp  --  eth4   *       0.0.0.0/0            255.255.255.255     udp spts:67:68 dpts:67:68 state NEW,ESTABLISHED
    8  4608 ACCEPT_LOG_ALL_7  udp  --  eth1   *       192.168.200.1        255.255.255.255     udp spts:67:68 dpts:67:68 state NEW,ESTABLISHED
Note:
According to the dhcrelay-manpages you need to specify the outgoing interface of the relayed DHCP-request as well as the incoming.

Unfortunately, I wasn't able to completely test dhcrelay in my environment.
I saw the request-packet on the external interface, but my router didn't send an answer :roll:

How do you configure DHCP relay from one subnet to another?

Verfasst: Fr 31.07.2009, 19:43
von ajl119
Thank you,

With your help I managed to get it working :)