Solved

Disable udp on ports 137 and 138 on cisco 1700

Posted on 2004-03-22
5
1,549 Views
Last Modified: 2007-12-19
Hi all. I've have a problem with workstations thinking they are the masterbrowser for my Windows 2000 domain. This is happening because I'm using ip helper addresses to broadcast dhcp requests on the router that connects another network on the same subnet . As a result, netbios udp broadcasts on ports 137 and 138 are also being forwarded, causing the master browser issue. What is the command to disable udp or broadcast forwarding on specific ports?
0
Comment
Question by:bluespringsit
5 Comments
 
LVL 51

Expert Comment

by:Netman66
ID: 10653625
Instead of using a helper address why not use a DHCP Relay agent on the subnet without the DHCP server?

This would be a better option - stops broadcast storms.

0
 
LVL 6

Expert Comment

by:parkerig
ID: 10653908
this is a real simple example I am giving so modify it as you see fit.

on cisco router
create an access list like

deny udp 137
deny udp 138
permit all

apply this access list to the ethernet port ( or whichever port connects lan / wan)

Cheers
Ian
0
 
LVL 79

Accepted Solution

by:
lrmoore earned 125 total points
ID: 10654010
The ip helper-address interface commands opens up those udp ports. You can close them back down easily enough without an access-list

router(config)#no ip forward-protocol udp 137
router(config)#no ip forward-protocol udp 138

0
 
LVL 51

Expert Comment

by:Netman66
ID: 10654047
lrmoore,

Perfect!

I still think a relay agent would work too, but your answer is simpler.

0
 

Author Comment

by:bluespringsit
ID: 10659426
Perfect, thank you lrmoore and everyone else. I went with the no ip forward commands instead of a relay agent. Theres only two computers on this other segment. Thanks again!
0

Featured Post

Gigs: Get Your Project Delivered by an Expert

Select from freelancers specializing in everything from database administration to programming, who have proven themselves as experts in their field. Hire the best, collaborate easily, pay securely and get projects done right.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Cisco Access point 6 87
Radius Debug Error 16 89
Cookies and new tab 3 36
Failing ALG SIP test for new VoIP phone system 4 82
Meet the world's only “Transparent Cloud™” from Superb Internet Corporation. Now, you can experience firsthand a cloud platform that consistently outperforms Amazon Web Services (AWS), IBM’s Softlayer, and Microsoft’s Azure when it comes to CPU and …
I had an issue with InstallShield not being able to use Computer Browser service on Windows Server 2012. Here is the solution I found.
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're looking for how to monitor bandwidth using netflow or packet s…

785 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question