Ethernet Frame Sniff-tastic!

Aug 15, 2005 3 Replies
Ethernet Frame Sniff-tastic! open original image

Hi all



Is there any way I can look at dot1q frames on a 'switchport' on a Catalyst 2950? I have a PC plugged into a Mitel phone but I need to ensure that the Priority/CoS stuff is set up correct.



Thanks for any help.



John T.


Good man.

I knew there would be a way, I'll look in to this.

Thanks, John T.

John,

You should set VLAN tagging on the Mitel IP phone, which will tag the Ethernet frames from the PC with one VLAN ID and the frames from the phone with a diferent VLAN ID. On the IP voice PBX you will want to set the IP precedence or DSCP value for IP voice packets to 5 or 45, respectively. The default CoS value that is assigned to all incoming untagged packets on the 2950 is 0. The switch also has a default DSCP-to-CoS mapping that is fine for most installations, but can be modified as necessary. Depending on the OS, you may also be able to do things like rewrite the ToS bits, set dscp values, and perform egress queuing at the switch. Alternatively you can modify IP headers (ToS), set CoS, and perform strict priority queuing at the router. Here is a link for configuring the 2950:

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Dan

On 15.08.2005 20:17 Marraboy wrote

SPAN (Switched Port Analyzer) or RSPAN is what you want.

You can analyze network traffic passing through ports by using SPAN to send a copy of the traffic to another port on the switch that has been connected to a SwitchProbe device or other Remote Monitoring (RMON) probe or security device. SPAN mirrors received or transmitted (or both) traffic on one or more source ports to a destination port for analysis.

See

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for details

Arnold

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