3.5 shutting FR subinterface causing backup interface being disabled?

Hi Guys,

According the the solution guide, we are disabling the frame relay main interface on R4 to trigger the backup interface to come up.

However when I try to disbale the frame relay subinterface, the backup point to point interface didn't come up instead it went to disabled mode? any idea?

 

before shut down the interface


Rack1R4#sh ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            204.12.1.4      YES manual up                    up
Serial0/0                  unassigned      YES unset  up                    up
Serial0/0.1                155.1.0.4       YES manual up                    up
FastEthernet0/1            155.1.146.4     YES manual up                    up
Serial0/1                  155.1.45.4      YES manual standby mode          down
Loopback0                  150.1.4.4       YES manual up                    up

After shut down the interface

Rack1R4#debug backup
Backup events debugging is on
Rack1R4#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Rack1R4(config)#int se0/0.1
Rack1R4(config-subif)#shut
Rack1R4(config-subif)#
*Mar  5 00:31:36.584: BACKUP(Serial0/0.1): event = primary interface shutdown
*Mar  5 00:31:36.588: BACKUP(Serial0/0.1): secondary interface (Serial0/1) moved to standby
*Mar  5 00:31:36.592: BACKUP(Serial0/0.1): changed state to "disabled"
*Mar  5 00:31:37.576: BACKUP(Serial0/0.1): event = primary interface went down
*Mar  5 00:31:37.576: BACKUP(Serial0/0.1): backup is currently disabled on this interface
Rack1R4(config-subif)#end
Rack1R4#sh
*Mar  5 00:31:42.996: %SYS-5-CONFIG_I: Configured from console by console
Rack1R4#sh ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            204.12.1.4      YES manual up                    up
Serial0/0                  unassigned      YES unset  up                    up
Serial0/0.1                155.1.0.4       YES manual administratively down down
FastEthernet0/1            155.1.146.4     YES manual up                    up
Serial0/1                  155.1.45.4      YES manual standby mode/disabled down
Loopback0                  150.1.4.4       YES manual up                    up
Rack1R4#sh backup
Primary Interface   Secondary Interface   Status
-----------------   -------------------   ------
Serial0/0.1         Serial0/1             disabled

 

 

Comments

  • Hi,

    I got the same issue. I think it is because you manually shutdown the interface. In that case IOS will not make the backup interface up. If you go ahead and bring the frame relay switch down, you can see backup interface in action. Another way is to shutdown remote end frame relay interface. Still you may see pvc is up because interface keeps on getting LMI from frame relay switch. So enable frame relay keepalive and shutdown the remote end.

    -Shameer

  • Hi Guys,

    According the the solution guide, we are disabling the frame relay main interface on R4 to trigger the backup interface to come up.

    However when I try to disbale the frame relay subinterface, the backup point to point interface didn't come up instead it went to disabled mode? any idea?

     

     

    Change the encapsulation method of the interface Serial 0/0 to
    something else lke in the following configuration and it will work.

    interface s0/0

    no encapsulation frame-relay

    encapsulation ppp

     

    On the Frame Relay switch, you can also delete the DLCI associated with the you FR subinterface.

     

    Hope this help!

  • Think this is devised to prevent you shutting down your main interface by mistake and then incurring quite expensive dial bills. Goes back to the good old days of ISDN and dial, when the dial interface (or the ISDN interface) was used as a backup to the main interface. Not ideal, but a great "get out of jail" card when your main interface goes down, and there is no other way to establish a connection. By preventing the backup interface coming up when the main interface has been administratively shut down, (which could occur, for example, when doing some maintenance out of hours), you avoid running up a hefty bill.



    As previously mentioned here, changing the encapsulation on the interface, or even changing the LMI-type to something other than which is alrfead configured on the network, will cause the primary link to go down, without it being administratively shut down.



    There is a great explanation for this in video "038-Backup Interface" in the Advanced Technologies series of videos, which helped me understand why the backup interface went into disabled mode. Like you, I'd have struggled to be honest with why it didnt automatically kick in when the main interface went down.

    Hope this makes sense?

    Kevin

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