Port monitoring

Unanswered Question


I have a network analyzer connect to a port on my 3550 switch, which I can access remotely via the web. When I configure the port for port monitoring, I can no longer access the network analyzer application via the web.

These are the commands I have entered to enable port monitoring:

no monitor session 1

monitor session 1 source interface fastethernet 0/32

monitor session 1 destination interface fastethernet 0/43

Port 0/43 is configured as follows:

interface FastEthernet0/43

description network analyzer

switchport access vlan 10

no ip address

duplex full

speed 100

no mdix auto

spanning-tree portfast

Is it not possible to connect to the PC ip address once port monitoring is enabled?



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ankbhasi Thu, 05/24/2007 - 10:17

Hi Mary,

Once you configure some port as destination monitor port the port goes into monitoring state and will only receive sniff packets from source monitor port.

If you want this destination port to also participate in network while capturing traffic enable a keyword "ingress" something like this

monitor session 1 destination interface fastethernet0/43 ingress vlan 10

To read more about ingress functionality read this link


Try this and update if it worked.



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ankbhasi Thu, 05/24/2007 - 10:52

Hi Mary,

It does not matter which vlan you are trying to monitor, what matters is that destination port should be configured with same vlan what you specify in span destination ingress vlan.

Is it possible for you to attach "sh run", "sh vlan" and "sh interface fa 0/43" and "sh version"?



ankbhasi Thu, 05/24/2007 - 11:21

Hi Mary,

All look good to me ..

Can you just add this line on your interfaces fa0/43 & interface fa0/32

switchport mode access

Also where you have configured monitored destination port from that config remove untagg keyword and let only this command be there

monitor session 1 destination interface Fa0/43 ingress vlan 10

If this does not work I will do some research and get back to you tomorrow on the same.



ankbhasi Thu, 05/24/2007 - 22:07

Hi Mary,

Its working for me on my switch so I believe it should also work for you.

The "switchport mode access" will put this interface in an access port as bydefault all ports are in dynamic desirable mode and try to form a trunk sending DTP packets.

Just run the same command with "no" keyword and then run again same command removing untagg keyword. The interface status will still show you monitoring but you should be able to ping your machine connected to your destination port.



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