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New Member

DLSW peers causing congestions

I noticed lately that my peers to the datacentre is causing congestions issues. Once I remove the peer or redirect it to another router performance on the WAN to the remote site improves.

This doesn't sound like a new issue can anyone relate?

  • Server Networking

Re: DLSW peers causing congestions

You need to identify the source of the traffic. In addition to LLC2 (i.e. SNA and NETBIOS) traffic, DLSw forwards LLC1 traffic if the routing protocol of the traffic is not enable on the router. For example, DLSw will forward IPX traffic if IPX routing is not enable on the router.

I suggest you one of the followings:

1. put a sniffer and identify the traffic source. Look for any traffic with UDP port 2067.

2. enter a global command "DLSW icanreach sap 00 04 F0." If you do not need to transport NETBIOS, please omit F0 from the above command.

3. another way is to enter global command "dlsw udp-disable"

New Member

Re: DLSW peers causing congestions

1. Betwwn the peers there dosen't seem to be any UDP traffic, I can only find 2065.

2. What will DLSW icanreach sap 00 04 f0 do?

3. I'm guessing this would be an IOS issue if I don't have that command.


Re: DLSW peers causing congestions

1. Cisco implements DLSw version 2 in 11.3. DLSw version 2 uses UDP for non-llc2 traffic. If one of the DLSw peers router use 11.2 software, you will not see UDP traffic on the DLSw pipe.

2. DLSw icanreach 00 04 f0 specifies SAP (service access point) transported by DLSw. 04 is the default SAP for SNA traffic. I have seen a couple of companies use other SAP value for SNA. F0 is the default SAP value for NETBIOS. In short, DLSW icanreach command is a filter to filter out all traffic, but SNA and NETBIOS, from DLSw. Very powerful command. Please go to the following URL for details:

3. As per above URL, DLSw icanreach is introduced in IOS 11.0. If you do not get the global command, you may run a pre 11.0 software. This is a big problem for you because any IOS version before 11.2 is not Y2K compliant. (Does anyone still care on Y2K?) Please verify the IOS version by using show version.

New Member

Re: DLSW peers causing congestions

The only time I have seen DLSw cause over-utilization issues is when the WAN interface is inadvertantly made part of the bridge-group servicing DLSw. If this is the case then ALL bridge traffic will span the wan and definately over-utilize it and the LAN it is dumping onto.




bridge-group 1


Re: DLSW peers causing congestions

I can think of several possibilities:

1. there are too many DLSw circuits on the router

2. the router picks up LLC1 (non-SNA and non NETBIOS) traffic

3. a DLSw loop

You may want to try DLSw icanreach sap 0 4. This will allow SNA. If you need NETBIOS (over DLC), you need f0 as well. Please go to the following URL on command reference: