I have a problem in configuring two pair of backup interface on my customer's router (3845). It's ok when I configure just one of them. If I configure both pairs of interfaces into backup interface, one of them will be in disabled mode, as shown below :
WANR01#sh ip int bri
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 172.16.199.106 YES NVRAM up up
GigabitEthernet0/1 172.16.3.5 YES NVRAM up up
Serial0/0/0 unassigned YES NVRAM administratively down down
Serial0/0/1 unassigned YES NVRAM administratively down down
FastEthernet0/1/0 188.8.131.52 YES NVRAM standby mode down
FastEthernet0/2/0 184.108.40.206 YES NVRAM standby mode/disabled down
FastEthernet0/2/1 220.127.116.11 YES NVRAM up up
Loopback0 172.16.199.12 YES NVRAM up up
Primary Interface Secondary Interface Status
----------------- ------------------- ------
GigabitEthernet0/1 FastEthernet0/2/0 disabled
FastEthernet0/2/1 FastEthernet0/1/0 normal operation
I was just working on a GNS3 lab for the CCIE R&S and got into a task where I should use this kind of Setup redundant interfaces and got the same result ( Got the disabled state).. In my case was because the primary interface was administrative shutdown.
Seems like when this happens the default action is to put the standby interface in shutdown state and it does not matter how many times you get into the backup interface and do a no shut... It will stay on that particular state
I would say that is expected as this works by monitoring the protocol line, not if I have shut it down or not...
Anyway just wanted to share that with anyone else having the same issue, looks like I have hit a wall as it does not matter if I take down the physical link the interface will keep as up. so GNS bug
Julio Carvajal Senior Network Security and Core Specialist CCIE #42930, 2xCCNP, JNCIP-SEC
I have also re-tested the backup interface feature on a 2691 router IOS. It seems that I have been too hasty in my first answer in this thread. Julio, you have been very kind to mark that answer as Cisco Endorsed but it does not really deserve the rating as it is misleading. I am not sure if you are able to un-mark that designation - if not, I will delete the entire response as it is wrong.
In any case, these are my findings:
If the main interface is up,up, the backup interface will be put into standby,down mode.
If the main interface is up,down or down,down, the backup interface will be put into up,up mode.
If the main interface is administratively down,down, the backup interface will be put into standby/disabled,down
It is not possible to manipulate the state of the backup interface using the shutdown or no shutdown command. This setting will always be carried over from the main interface.
The last point in particular shows that my former assessment of the situation was wrong. It would not be possible to deactivate the Fa0/2/0 interface as I originally suggested.
So this leaves me puzzled. A backup interface is in disabled state only if the main interface is shutdown. However, the OP's post shows that the main interface Gi0/1 is up,up while the backup interface Fa0/2/0 is disabled. This is clearly not logical. An IOS bug, perhaps?
If we manually shutdown the primary interface, backup interface will go to disabled. To work it properly, i changed the (serial interface) encapsulation to ppp (other end = hdlc), so for primary interface only protocal went down and backup link became up with below deb logs -
R1(config)#int s1/0 R1(config-if)#enc R1(config-if)#encapsulation ppp R1(config-if)#encapsulation ppp R1(config-if)#end R1# R1# *Mar 1 00:14:27.551: %SYS-5-CONFIG_I: Configured from console by console R1# *Mar 1 00:14:27.723: BACKUP(Serial1/0): event = primary interface went down *Mar 1 00:14:27.727: BACKUP(Serial1/0): changed state to "waiting to backup" *Mar 1 00:14:28.719: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/0, changed state to down R1# *Mar 1 00:14:28.719: BACKUP(Serial1/0): event = primary interface went down R1# *Mar 1 00:14:30.727: BACKUP(Serial1/0): event = timer expired on primary *Mar 1 00:14:30.731: BACKUP(Serial1/0): secondary interface (Serial1/1) made active *Mar 1 00:14:30.731: BACKUP(Serial1/0): changed state to "backup mode" R1# *Mar 1 00:14:32.727: %LINK-3-UPDOWN: Interface Serial1/1, changed state to up R1# *Mar 1 00:14:32.735: BACKUP(Serial1/1): event = secondary interface came up *Mar 1 00:14:33.731: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/1, changed state to up R1# *Mar 1 00:14:33.731: BACKUP(Serial1/1): event = secondary interface came up R1# R1# R1# R1# R1#sh ip int brie Interface IP-Address OK? Method Status Protocol FastEthernet0/0 unassigned YES unset administratively down down FastEthernet0/1 unassigned YES unset administratively down down Serial1/0 18.104.22.168 YES manual up down Serial1/1 22.214.171.124 YES manual up up Serial1/2 unassigned YES unset administratively down down Serial1/3 unassigned YES unset administratively down down
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