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Community Member

port errors on 5509

Is there a way to switch a 5509 to store and forward mode, so when I span a port I can see the errors come in on a port? I have a remote sniffer attached to the switch to save me from going to the remote location. But I can't see the errors comming from the hub because the switch kills those packets. The counters on the port are nice but are not much help to identify who doing what. You can change the mode on a 3200 but I see no command to change it on a 5505. Thoughts/ideas anyone?

Community Member

Re: port errors on 5509

you don't need to change mode in this case

first, make sure there are no other span session running

switch(enable)set span disable

switch(enable)set span inpkts enable

example : set span 3/1 3/2 inpkts enable

there are also other option you could use.

just type set span 3/1 3/2 ?

good luck !

Community Member

Re: port errors on 5509

Thanks for the info but I still see no errors on the sniffer. Though the counter on the switch sees them. Of course if the errors occur before the first 2 bytes of the destination mac, the sniffer wont see it. I'll keep


Community Member

Re: port errors on 5509

You may need a Tap instead of a span port. lebrasseur is correct. A span port must be set up properly first, however span ports DO NOT see all traffic because the switch will drop packets that are too short or other types of errors.

You need to read this wonderfully written pdf on the subject of Taps Vs. Span:

Specifically, read the paragraph here from that pdf->

"...In contrast, a monitoring device connected to a SPAN port on a switch does not see all traffic. Corrupt network packets, or packets below minimum size, are usually dropped by the ingress ports on a switch; corrupt packets visible to the monitoring device are usually generated within the egress segment. In addition, switches eliminates layer 1 and select layer 2 errors. Without this information, it is impossible to properly troubleshoot common physical layer problems such as bad frames generated by a faulty NIC.

Additionally, the 5509 is a store-and-forward switch. Here's the doc that says that ->

Community Member

Re: port errors on 5509

Thanks for the info. After I submited the question I thought "hey stupid, it is in store and forward. I need it to be in cut through. DUHHHHH. Normally I would just take the portable sniffer out and attach it to the hub. In this case somebody "hijacked the closet" and we have to search far and wide to get somebody to open the door. Well if it was easy anybody could do it. Thanks again for the info

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