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Impact of applying ip forward-protocol udp port#

karamalomari
Beginner
Beginner

I have multiple Layer 3 SVI configured on the core switch and all of them are configured with "ip helper-address" command which by default enables "ip forward-protocol".

Now we have a requirement to add "ip forward-protocol udp PORT#" command.

when using "ip helper-address" then following UDP ports are enabled by default:
1) TFTP-69
2) DNS-53
3) Time-37
4) Netbios name services-137
5)Netbious datagram services-138
6)BOOTP server-67
7)Bootp client-68
Tacacs-49

What will be the impact of adding "ip forward-protocol udp PORT#"? Will this impact the default ports enabled by the "ip helper-address" method?

3 Replies 3

MHM Cisco World
VIP Mentor VIP Mentor
VIP Mentor

NO
the new UDP port will add to UDP default port that router will forward it.

rasmus.elmholt
Rising star
Rising star

No,

The new port will only be added to the list and if your SVI receives a packet on the port it will be forwarded to all the helper-addresses configured.

balaji.bandi
VIP Community Legend VIP Community Legend
VIP Community Legend

I do not see any effects - ip forward protocol

Enabling a helper address or UDP flooding on an interface causes the Cisco IOS software to forward particular broadcast packets. You can use the ip forward-protocol command to specify exactly which types of broadcast packets you would like to have forwarded. 

If you use the ip forward-protocol command, specifying only UDP without the port enables forwarding and flooding on the default ports.

some reference :

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-i1.html#wp1776761080

 

BB

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