Routing with Point to Point Connection

Unanswered Question

Hi Guys,

I need you help. Here is my situation.

I have two LANS spread over a geographical area which I would like to connect.

On Network A, I have Internet connection, dhcp server, Cisco 2800 Series router, Cisco 2960 Series switch, exchange, file server and so on.

On Network B, I have the same thing as network A but no exchange.

Anyways, Network A has an internal IP of and Network B has an Internal Network of

I have purched a leased line or point to point connection between the two locations but what i want to do is I want each location to use its own dhcp and internet connection but still be able to access resources from each others network. How can i do this?

I tried just connecting the point to point into the cisco switch in on location and the same on the other side. The plus side is that I can see the other network from one end. However as soon I attach the dhcp my network will either fail on one side or one dhcp server will become the dominate and will start sending addresses to the other side. How can i prevent this.

Also, Network A has a domain controller, so i want network B to be apart of this domain. Is this possible?

I did some research and some say it is possible through VLANS and trunking. However when i tried this I got the result mentioned above.

Please Help


Donny Q

I have this problem too.
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Giuseppe Larosa Fri, 11/20/2009 - 11:53

Hello Donny,

to keep separated the two sites from DHCP point of view should be enough to apply the appropriate ACL on the WAN point to point link if this link is a L3 routed link.

DHCP uses BOOTP messages that use UDP port 67 and 68

access-list 111 remark no dhcp and bootp

access-list 111 deny udp any any eq bootpc

access-list 111 deny udp any any eq bootps

access-list 111 permit ip any any

this access-list can be applied on the wan links

this should be able to stop DHCP servers competition

but I have a doubt that your link is a L2 link and not a L3 link otherwise an even easier solution is to have on siteA:

only ip helper-address serverA

for siteB only ip helper-address serverB

if you have two different IP networks at the two sites you need to have a routed link between the two sites.

That would be a firewall for DHCP requests that are sent to broadcast.

routers can translate DHCP requests to have them routed with the ip helper-address given in interface configuration mode.

Hope to help



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