Switches Connectivity Via Transport MUX

Unanswered Question
Apr 21st, 2009


Is there any provision/command in cisco switches (we are using 4507 L3 switches)... where in case of transport failure between two Muxs (switches are not directly connected to each other, they are connected via transmission MUXs at both end), The connected GIG port on both cisco switches will go down.

Note :- Asking this question as Both the switches are not directly connected , MUX involved in between connectivity... and in our case ports are not going down even there is failure of connectivity between MUXs.

I am looking for a solution, where in case of transport connectivity failure between MUXs, anyhow Switches at both end detect the outage and keep their Gig port auto Shut. So that traffic on that link will shifted to alternate path within seconds

Scenerio attached here for easy understanding.


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vmiller Tue, 04/21/2009 - 07:45

A few questions.

Who owns the muxes and their respective configurations?

What is the transport between the two Muxes? i.e. Gig/E ?

cisco.net Tue, 04/21/2009 - 08:35


MUXes & their configs are owned & maintained by Services Provider.

Fiber ring between MUXes. In my above question i am querring about Gig port connectivity.

vmiller Tue, 04/21/2009 - 12:29

If you route between the two endpoints, a link failure would be recognized by your gig port. Unless there is some way for the provider to drop the link between your switch and the mux based on a failure of the link between the mux.

NickNac79 Tue, 04/21/2009 - 23:29


This one is dead easy - we had the same issue using LES / EES circuits over here.

Create a single-member port-channel with LACP (The Following commands assume the link is a trunk):

interface port-channel 1

switch trunk enc dot

switchport mode trunk

interface GigabitEthernet1/3

descr Po1: MUX Link

switch trunk enc dot

switch mode trunk

channel-group 1 mode active

Do this on both ends of the MUX link - the LACP will bring PO1 down if there is any loss of connectivity.

Hope this helps!

Please rate any useful posts.


cisco.net Wed, 04/22/2009 - 00:13

Thanks Nick,

please confirm what this command will do "switch trunk enc dot".


NickNac79 Wed, 04/22/2009 - 00:38

switchport trunk encapsulation dot1q

When the port is in trunking mode, the encapsulation used will be 802.1q - instead of ISL

On some devices / IOSs this command isn't needed/accepted because they always use dot1q. If your device doesn't accept the command - then it already uses dot1q.


cisco.net Wed, 04/22/2009 - 01:20

Hii Nick,

I guess, we already used this scenerio. But unfortunerly not helping out for our expectation.


NickNac79 Wed, 04/22/2009 - 01:36


In what way is it not working?

Have you got the port-channel up?

What happens to the port-channel when the MUX goes off?


cisco.net Wed, 04/22/2009 - 02:47

Port Channel and respective Gig port always showing UP even in case of failure of transport.

NickNac79 Wed, 04/22/2009 - 03:28


It sounds like you've not got LACP turned on unconditionally.

You need to have:

channel-group 1 mode ACTIVE

if you have anything else, like auto, on or passive this will not work.

The Gig interface will always show as up - only the port channel will go down.


cisco.net Thu, 04/23/2009 - 04:48

Hii Nick,

I can understand this. But this LACP sceneio also not helping


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