Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

IP helper address

Recently we started using IP helper to get the DHCP from a centralized DHCP. I guess it is causing an issue with Windows 2k machines. The lan group is advising me that it is broadcasing PORT 137 and PORT 138.

I guess every 13 minutes they try to negiotate a master browser.

How can I stop ports 137 and 138.


Re: IP helper address

Router#config terminal

Router(config)#no ip forward-protocol udp 137

Router(config)#no ip forward-protocol udp 138


Re: IP helper address

From the documentation

To specify which protocols and ports the router forwards when forwarding broadcast packets, use the ip forward-protocol global configuration command. To remove a protocol or port, use the no form of this command.

ip forward-protocol {udp [port] | nd | sdns}

no ip forward-protocol {udp [port | nd | sdns}

If a helper address is specified and UDP forwarding is enabled, broadcast packets destined to the following port numbers are forwarded by default:

Trivial File Transfer Protocol (TFTP) (port 69)

Domain Naming System (port 53)

Time service (port 37)

NetBIOS Name Server (port 137)

NetBIOS Datagram Server (port 138)

Boot Protocol (BOOTP) client and server datagrams (ports 67 and 68)

TACACS service (port 49)

IEN-116 Name Service (port 42)

New Member

Re: IP helper address

Tks everyone , that has done the trick.