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New Member

Any TECKI can HELP me on Sniffing SPAN Port?

Does CAT6509 pass VLAN header received from the SOURCE-SPAN port (dot1q trunk port) to the DEST-SPAN port (dot1q trunk port) if both SOURCE-SPAN and DEST-SPAN ports belongs to same VLAN?


2 Source-SPAN ports: 6/42 adn 6/43 - 100bTFull- VLAN100-dot1Q trunk port

1 Dest-SPAN port: 6/33 - 100bTFull - VLAN100-dot1q trunk port

Attached Sniffer to 6/33


Host connected to the 6/42 and 6/43 sends 802.1/Q header to the CAT6509.

Want to verify that using SPAN feature ONLY not w/ HUB


Do not see VLAN header for VLAN99 but see other VLAN headers. I guess that is beacuse of source ports 6/42 and 6/43 are tunk ports and they might be getting frame/pkt from different VLAN ( other then 99) so it is seen.

Any NEW suggestions OR comments!


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New Member

Re: Any TECKI can HELP me on Sniffing SPAN Port?



Finally i got it worked.


SPAN dest port/s has to be in the different VLAN form the source SPA port that

you want to Sniff. For example: If you want to moirror source ports 6/42 and 6/43 (TRUNK) ports of VLAN 99 TO the SPAN dest (TRUNK) port 6/33, Then put the SPAN dest port 6/33 in VLAN=3 (or other then VLAN=99). This would let switch to pass the VLAN header info of source ports (VLAN=99) onto the SPAN dest port of (VLAN=3).


My understanding is...

If source and dest SPAN ports are in the same VLAN then CAT6509 does not pass the VLAN header onto the dest SPAN port because of host of same VLAN. eventhough all source and dest ports are TRUNK ports.

Any comments on???