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Cisco 1604-r DNS using NBT (137)

By chicharones ·
Need help. Netbios is using dns(53) for name resolution(137) thus bringing up our Isdn line.

I already tried using an access list and dialer list

access list 101 deny udp any any eq 137
dialer list 1 protocol ip list 101

This is what thesniffer found.


UDP: ----- UDP Header -----
UDP:
UDP: Source port = 137 (NetBIOS-ns)
UDP: Destination port = 53 (Domain)
UDP: Length = 55
UDP: Checksum = 62B6 (correct)
UDP: [47 byte(s) of data]
UDP:
DNS: ----- Internet Domain Name Service
Anyway is there anybody out there that can come up with a different filter to filter this traffic?

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Cisco 1604-r DNS using NBT (137)

by Some Guy in Seattle In reply to Cisco 1604-r DNS using NB ...

To block this specific traffic you would need the following command:

access list 101 deny udp any any eq 53

Cisco access lists filter by default on the destination port, not the source.

Hope that helps -

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Cisco 1604-r DNS using NBT (137)

by chicharones In reply to Cisco 1604-r DNS using NB ...

The question was auto-closed by TechRepublic

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Cisco 1604-r DNS using NBT (137)

by guru@net In reply to Cisco 1604-r DNS using NB ...

The last answer is correct, but this will also deny the DNS queries that you want to pass the router (i.e. resolution for web surfing). Unless you have your own internal DNS to resolve Internet names, then I suggest that you disable "use DNS for NetBIOS name resolution" on all of your hosts.

HTH

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Cisco 1604-r DNS using NBT (137)

by chicharones In reply to Cisco 1604-r DNS using NB ...

The question was auto-closed by TechRepublic

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Cisco 1604-r DNS using NBT (137)

by chicharones In reply to Cisco 1604-r DNS using NB ...

This question was auto closed due to inactivity

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