SPAN monitoring

Unanswered Question
Jun 9th, 2009

Hi all,

I have configured SPAN on 3750 switch and couldn't see any L2 protocol updates on destination it normal behaviour

and I am aware on this

# A destination port does not participate in spanning tree while the SPAN session is active.

# When it is a destination port, it does not participate in any of the Layer 2 protocols (STP, VTP, CDP, DTP, PagP).

but question is I should see L2 protocols info of source interfaces i am trying to monitor ?


I have this problem too.
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Giuseppe Larosa Tue, 06/09/2009 - 03:49

Hello Shiva,

yes it is normal to see L2 protocols frames you need the option

encapsulation replicate on config of destination port

It says:

The default configuration for local SPAN session ports is to send all packets untagged. SPAN also does not normally monitor bridge protocol data unit (BPDU) packets and Layer 2 protocols, such as Cisco Discovery Protocol (CDP), VLAN Trunk Protocol (VTP), Dynamic Trunking Protocol (DTP), Spanning Tree Protocol (STP), and Port Aggregation Protocol (PAgP). However, when you enter the encapsulation replicate keywords when configuring a destination port, these changes occur:

•Packets are sent on the destination port with the same encapsulation-untagged, Inter-Switch Link (ISL), or IEEE 802.1Q-that they had on the source port.

>>>•Packets of all types, including BPDU and Layer 2 protocol packets, are monitored.

Hope to help



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