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Blocking DHCP Forwarding packet

We have 2 Routers.The Remote Router(2600) sends the DHCP relay and forwarding packets to the Main Router(4700M).The DHCP forwarding packet has a Gateway IP address of 0.0.0.0.When the packets are relayed with special processing,why do they get forwarded also with no special processing.Is there a way we can block the DHCP forwarded packets alone going from remote site router to Main site router.Is there a selective access-list for doing that.

Thanks.

Anu

3 REPLIES
Silver

Re: Blocking DHCP Forwarding packet

Anu,

Routers do not, by default, forward DHCP requests. ip-helper is most surely configured on your remote router, unless your bridging. Can you just remove or change this ip-helper to suit your needs? Access-lists to stop these might very well effect other things that you might want to pass. If you really want to use an ACL you can deny ip from the primary ip address of the remote router's interface, which is used to encapsulate the DHCP request (DISCOVER)..

Hope this helps,

Don

New Member

Re: Blocking DHCP Forwarding packet

Don

Can a IP DHCP Relay command be applied in this regard instead of the Ip helper address.But I am not sure if we can configure IP addresses with the IP Dhcp Relay Command.

Thanks

Anu

Re: Blocking DHCP Forwarding packet

I think the DHCP relay command , can be used if the server is a Cisco IOS DHCP server. As Don suggested, you might want to either remove the helper-address or block the dhcp packet using accesslists.

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