?
Solved

Disable udp on ports 137 and 138 on cisco 1700

Posted on 2004-03-22
5
Medium Priority
?
1,597 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
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
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 500 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

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

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

Originally, this post was published on Monitis Blog, you can check it here . It goes without saying that technology has transformed society and the very nature of how we live, work, and communicate in ways that would’ve been incomprehensible 5 ye…
This article will show how Aten was able to supply easy management and control for Artear's video walls and wide range display configurations of their newsroom.
If you're a developer or IT admin, you’re probably tasked with managing multiple websites, servers, applications, and levels of security on a daily basis. While this can be extremely time consuming, it can also be frustrating when systems aren't wor…
Monitoring a network: why having a policy is the best policy? Michael Kulchisky, MCSE, MCSA, MCP, VTSP, VSP, CCSP outlines the enormous benefits of having a policy-based approach when monitoring medium and large networks. Software utilized in this v…
Suggested Courses

752 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