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What is "ip forward-protocol udp netbios-ss"

Posted on 2007-04-03
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Last Modified: 2009-07-29
I have this command listed on the configuration of our Cisco 4507R layer 3 switch.
"ip forward-protocol udp netbios-ss"
What exactly does this do?
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Question by:Spelurker
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Bobby_Thekkekandam earned 500 total points
ID: 18844968
Very simply put, "ip forward-protocol udp netbios-ss" enabled forwarding of netbios session service (port 139) broadcast packets for interfaces configured with an ip helper.

To provide a more detailed explanation, the ip forward-protocol global configuration command combined with the ip helper-address command allows you to control which broadcast packets and whichi protocols are forwarded. If you use the ip forward-protocol command, specifying only UDP without the port enables forwarding and flooding on the default ports (TFTP, DNS, Time, NetBIOS name server, NetBIOS datagram server, BOOTP, TACACS).

So specifying netbios-ss explicitly makes the 4507 forward any NetBIOS session service broadcast packets.

Hope that helps,

Bobby
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by:Spelurker
ID: 18845039
Bobby,
I do have the ip helper-address command listed for several of my internal VLANs. As I understand it, that points machines to the ip address of a DHCP server on another subnet or VLAN. If I remove the "ip forward-protocol udp netbios-ss" command, will that screw up the ability to retrieve DHCP for those VLANs or merely stop these 'netbios' broadcasts?
Thanks.
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by:Bobby_Thekkekandam
ID: 18845088
Hi,

removing netbios-ss forwarding will only stop the forwarding of NetBIOS broadcasts. It will not affect DHCP.

HTH,

Bobby
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