07-15-2012 12:31 PM - edited 03-04-2019 04:58 PM
OK Experts,
I have made this issue very simple for you guys to help me out.
I have two routers R22 and R23. I have configured the back up interface on R22 to be interface fas 0/1. Everything appears to be working fine. I issue the command show backup and I get the following on R22
r22#show backup
Primary Interface Secondary Interface Status
----------------- ------------------- ------
FastEthernet0/0 FastEthernet0/1 normal operation
r22#
Also I get the following:
FastEthernet0/1 10.10.13.2 YES manual standby mode down
However, when I shutdown interface fast 0/0 to test the back up interface fast 0/1 I get the following:
r22#show backup
Primary Interface Secondary Interface Status
----------------- ------------------- ------
FastEthernet0/0 FastEthernet0/1 disabled
r22#
FastEthernet0/1 10.10.13.2 YES manual standby mode/disabled down
So it doesn't work.
Attached are the configs.
I was wondering if someone could help me figure out why this won't work.
Cheers
07-15-2012 02:58 PM
Hello Carlton,
there are some notes about your tests:
a) the configuration of the primary interface includes two logical interfaces main interface and a vlan based subinterfaces both fail when you disable fas0/0, the secondary interface has only IP configuration at main interface level
from your log files:
interface FastEthernet0/0
backup interface FastEthernet0/1
ip address 10.10.14.2 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 12
ip address 10.10.12.2 255.255.255.0
!
You should remove the subinterface fas0/0.1 as a minimum to make interface configurations compatible,
b) the specific type of interface you would like to use for backup is LAN based Fastethernet.
The backup command had been introduced for providing a backup interface for serial interface and the secondary interface may be a serial interface or ISDN based ( in this case a DDR call is triggered over ISDN).
The dial backup command reference says that support for gigabit interfaces in C7600 has been later introduced.
see
http://www.cisco.com/en/US/docs/ios/dial/command/reference/dia_a1.html#wp1012054
The use of backup command may be supported or not for fastethernet interface on your routers.
If it is not supported, you can easily implement an alternate solution, because you are running OSPF in area 0 in all router interfaces
router ospf 1
log-adjacency-changes
>>network 0.0.0.0 255.255.255.255 area 0
!
So all you need to do is to increase OSPF cost on fas0/1 to create a backup path
on R22, R23:
conf t
interface fas0/1
ip ospf cost 50
Hope to help
Giuseppe
07-15-2012 04:31 PM
Carlton
In my experience with backup interface one of the lessons that I learned is that you can not test it by doing shutdown on the primary interface. It seems that IOS is smart enough to say that if you shut down the interface it was intentional and therefore it does not activate the backup interface. I suggest that you test by creating a real problem on the primary interface. (unplug is the first thing that comes to mind but there are probably other things that might work)
HTH
Rick
Sent from Cisco Technical Support iPad App
07-16-2012 01:26 AM
Hi Giuseppe,
Thanks for responding, I did try the backup interface solution without sub-interfaces and I got the same results.
I wonder if you're correct when you mention that 'backup interface' was introduced to backup a serial interface?
Increasing the ip ospf cost is a solution I will investigate.
Cheers
07-16-2012 01:41 AM
Hi Carlton,
Follow Rick advice because as he stated the backup interface can't be put out of standby mode by shutting down the primary interface, this was made on purpose because at the beginning the backup interface was a link you were paying for only when traffic was flowing and it was expensive and so to prevent using that line by just doing a mistake and shutting down the primary they conceived it like this.
Regards.
Alain.
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07-16-2012 02:21 AM
Hi Cadet,
I'm back in the office now and will setup the backup interface in our lab.
In the meantime, apart from actually disconnecting the cable, is there another way of testing backup interface?
Regards
Carlton
07-16-2012 02:45 AM
Hi,
just shut down the primary interface on the other router.
Regards.
Alain
Don't forget to rate helpful posts.
07-16-2012 03:26 AM
cadet,
I tried your suggestion by shutting the primary interface on the other router.... However, the backup interface still didn't activate.
R10#show backup
Primary Interface Secondary Interface Status
----------------- ------------------- ------
FastEthernet0/0 FastEthernet0/1 disabled
I think I will have to pull the cable. If that doesn't work I will then assume it won't work with the primary and backup interface both being ethernet???
07-16-2012 04:12 AM
Hi,
is there a switch between the 2 devices ?
Regards.
Alain
Don't forget to rate helpful posts.
07-16-2012 04:42 AM
Carlton
I am not authoritative on this, but I believe that backup interface should work with Ethernet interfaces. And a couple of things from your original post see to indicate that it is ok
r22#show backup
Primary Interface Secondary Interface Status
----------------- ------------------- ------
FastEthernet0/0 FastEthernet0/1 normal operation
r22#
Also I get the following:
FastEthernet0/1 10.10.13.2 YES manual standby mode down
If backup interface was not supported on Ethernet then I would not expect to get these outputs.
With serial interfaces there were a couple of things that we could do to create a problem that would initiate the backup interface (things like changing the line encapsulation or turning off keepalives on the neighbor device). But those do not affect Ethernet. On a router I would have thought that shutting down the interface on the directly connected device would have caused the Ethernet to go line protocol down. But the most reliable test is to unplug the router interface.
HTH
Rick
07-16-2012 06:05 AM
Hi Rick,
Unplug the router interface maybe my only option, however it should work by shutting down both interfaces...
07-16-2012 06:03 AM
No switch between.
05-18-2014 01:27 PM
Hi,
The configurations on the primary and backup interfaces must match or the backup interface does not work.
BR,
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