Impact of applying ip forward-protocol udp port#

[karamalomari]

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?

[MHM Cisco World · Accepted solution]

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

[rasmus.elmholt]

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 · Accepted solution]

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