SPAN not supported on some routed interfaces?

[Venison Mogambi]

Hi,

I'm trying to configure a SPAN session on a Cisco 3725 router, but it won't let me complete the command. The router has two Fast Ethernet interfaces: 0/0 and 0/1. I'm trying to configure a SPAN session with Fa0/0 as the source interface and Fa0/1 as the destination interface.

Here is the "show ip interface brief", showing my interfaces:

3725_Router#sh ip int b

Interface                  IP-Address      OK?           Method          Status                               Protocol

FastEthernet0/0         x.x.x.x           YES            NVRAM           up                                    up

FastEthernet0/1       unassigned      YES          NVRAM             administratively down     down

But when I try to configure the session, it seems like it's giving me the option to configure the SPAN session, but in the end the router won't let me:

3725_Router(config)#monitor session 1 source interface ?

  FastEthernet  FastEthernet IEEE 802.3

  Port-channel  Ethernet Channel of interfaces

3725_Router(config)#monitor session 1 source interface FastEthernet ?

  <0-2>  FastEthernet interface number

3725_Router(config)#monitor session 1 source interface FastEthernet 0/0

                                                                                       ^

% Invalid input detected at '^' marker.

When I type "?", why would it give me the option of using the Fast Ethernet interface as source port, then when I try to execute the command, it doesn't like it?

Has anyone experienced this? Is it not supported on this chassis, or maybe my IOS?

Thanks.

[Anand G]

Hi Venison,

I had a look at your case and tried in my lab. I am getting a different error, but accepting the other parameters where you got rejected by router.

Could you please provide the image you use or 'show ver' output please?

Let me have a check and revert you ASAP.

Regards,

Anand G (ag2)

[Venison Mogambi]

Hi Anand,

The IOS I'm using is c3725-advipservicesk9-mz.124-25d.

Thanks.

[Anand G]

Hi Venison,

This 3725 is a pure L3 router and its onboard motherboard has a capability to function as L3 only and NOT L2.

As you are aware that Span is pure L2, it doesn't support on 3725 router, which will act as pure L3 device.

But still, we can use the 3725 as L2 by inserting the NM-16ESW module or any other Ether Switch Network Module.

With the help of NM module (pure L2), we would be able to configure the Span.

You can check on the below URL for more details and various models.

http://www.cisco.com/en/US/prod/collateral/routers/ps259/product_data_sheet09186a00801aca3e.html

Regards,

Anand G.

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[cadet alain]

Hi,

SPAN is a L2 port feature so I don't think it will work with a routed port but you could try RITE feature:

http://www.cisco.com/en/US/docs/ios/12_4t/12_4t11/ht_rawip.html

Regards.

Alain

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[Venison Mogambi]

Hi Alain,

I've definitely read some documentation that says SPAN can work on both switched and routed ports, but maybe it doesn't work with this particular chassis and IOS.

Thanks for the RITE suggestion - I'd never heard of it.

Venison.

[glen.grant]

   Cadet is correct span will not work on a "built in" routed port.  If you have installed a hwic l2/l3 switch card in the router then that is a different matter and span will work on the switchcard whether routed or a layer 2 port .  But the span function was never built in on standard interfaces specially on EOL routers like the 3725.  The RITE feature appears to be for only newer routers like the 2800, 3800 series .  I'd never heard of that either, interesting.

[cadet alain]

Hi Glen,

I've tested  RITE  on a 3725 with GNS3 and it works.

Regards.

Alain

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