Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

dhcp across two network


We are running into a problem with dhcp. Diagram is attached here.

portion on the left side belongs to Network A & right side is network B. These two networks are seperated by Firewall B.

Firewall B has minimal rules & permits traffic between the two Network A & B. On network B , 6506 does all routing.

The edge switch in Network B has users connected to it. But these users(vlan50) connected to this edge switch are actually belonging to Network A, they are physically attached there.

Layer 3 interface Vlan 50 - is configured on the Firewall A & on its interface , dhcp relay is pointed to ( dhcp server).

Firewall A does all routing for this portion in Network A.

Appropriate routing is in place on both sides. We have created vlan 50 ( layer 2 ) in Core 6506 in Network B.

We are trying to see if  these users (in vlan 50- can get an ip address via dhcp server from Network A.

This proves to be unsuccessful.

It will be really helpful if people can help us out.

Thanks in advance.


Re: dhcp across two network

Do you have a helper address configured on vlan 50's SVI on the 6506 on Network B? If not, it should be pointing to You may have to allow udp destined for for bootpc through the firewall for it to allow that traffic through.


*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
New Member

dhcp across two network

John, thanks for the reply.

Layer 3 for Vlan 50 - /24 is configured on Firewall A . The 6506 only has vlan 50 in its layer 2 database.

Helper address/relay pointing to is configured on Vlan 50 interface on Firewall A.

Both the firewalls have the broad rules which permit all traffic in between these two segment of network.

Appreciate all inputs.

dhcp across two network


As John said you have to add on 6506 on network B ip helper under SVI VLAN 50 interface to make this work. Also is dhcp server accessible from network B?

Hope it will help.

Best regards,

Hope it will help. Best regards, Abzal
CreatePlease to create content