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Webcast-Catalyst9k
New Member

ip helper-address

Can I forward only DHCP broadcast to server 1 and only TFTP broadcast to server 2?

Client

|

|

Router --- Server1

|

|

Server2

I know that by default

ip helper-address X.X.X.X

forwards 8 protocols and I can get the rid of them using the

no ip forward-protocol udp 37

no ip forward-protocol udp 49

...

But in case of multiple helper-address, how to enable only one protocol per destination IP?

Thanks to read!

5 REPLIES

Re: ip helper-address

hello,

i think by using two helper address command with appropriate server addresses and by allowing appropriate udp port number you can achive it.

rate this post if it helps

regards

Devang

New Member

Re: ip helper-address

If I use 2 ip helper-address and I leave enabled 2 protocol to be forwarded, both bradcast will be forwarded to both destinations.

I haven't tried yet, but can an access-list in output sort this out?

Hall of Fame Super Gold

Re: ip helper-address

Stefano

I do not believe that there is any way to send only one type of message to one server and a different type of message to another server. I do not believe that an access list will do that either - but you are welcome to test it and let us know the outcome.

You can use ip forward-protocol/no ip forward-protocol to control what kind of messages get forwarded by ip helper-address. But whatever set of messages are enabled are sent to each server.

HTH

Rick

Gold

Re: ip helper-address

I don't think you will be able to filter messages that are produced by the router itself with a access list.

A method that should work is to use

IP LOCAL POLICY ROUTE-MAP xxxx

Route-map xxxx

Match IP address test

set interface null 0

ip aceess-list extended test

Permit udp any host x.x.x.x eq 37

permit udp any host x,x,x,y eq 49

Deny ip any any

In this case what you permit is dropped.

For those of you who have not used the local policy routing make sure you try it on a lab router first you can easily lock yourself out of the router.

Re: ip helper-address

hi

here you are matching the traffic for the perticular server and then by accesslist you are selecting the traffic of UDP port and then you divert that trafice to NULL 0 by using route maps

am i right?

regards

Devang

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