Cisco recommended that I patch my routers and switches IOS by blocking Blaster and Nachi ports 135, 139, even 69...
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and ICMP. But doesn't Microsoft's WINS service use some of these ports? My users now cannot see their domains, and I have a feeling it's because I'm blocking ports that they need, including some applications. What should I do?
Yes, I agree the Cisco recommendation is bad. And yes, you will block critical Windows ports that will not allow any Windows type of connections. I believe this was a first step by Cisco to stop the spread of malicious code. Now I think there is an IOS patch that will fix the problem within the router and switches, so you don't need to block them.
Furthermore, I think Cisco was making a general statement for fast fix so they could then update the IOS.
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