HSRP interface tracking

Unanswered Question
Jul 17th, 2008

What is the difference between tracking a sub-interface configured for VLAN and simply tracking a physical interface?

For e.g.

standby track FastEthernet0/0.5


standby track FastEthernet0/0

According to my understanding the second option automatically satisfies the first.

Is there a real significance of tracking a sub-interface instead of the corresponding physical interface?

What is the best practice?

Thanks in advance for your thoughts and time.

I have this problem too.
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lamav Thu, 07/17/2008 - 06:24

I've never tracked a sub-interface. But to answer the larger question, a physical interface can be "up, up" while one of its sub-interfaces can be down. Losing a Frame Relay DLCI is a perfect example.



tdrais Thu, 07/17/2008 - 06:33

For ethernet it is mostly true. There is probably a case where a subinterface could be down and the main up but it would have to be something strange related to the VTP tables.

In general it does little good to even track ethernet interfaces. They tend to stay up all the time even when stuff if very broke. The SLA track options are so nice when dealing with issue like this.

rsgamage1 Thu, 07/17/2008 - 06:47

Thanks a lot Victor for your excellent example.

For the moment, my Focus is on Ethernet.

Tracking sub-interfaces would be helpful in a scenario where there are several virtual interfaces configured to connect to different networks.

For instance, bringing down some networks for maintenance or when there's a new interconnection to be commissioned, could be taken.

Simply shutting down the sub-interface will lead to Standby router taking over for the link in discussion.

Since the Physical interface is up, the new link could be commissioned without any service interruption to the existing connection.

I understand this example is quite specific.

Though, my original post was made expecting some generic approaches/best practices with regard to HSRP interface tracking.


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