backup interface

[carl_townshend]

when I use this command, does it automatically route through it ? how would i put my static routes in this case, would I need 2, 1 for the normal interface and 1 for the backup interface ?

cheers

[devang_etcom]

carl,

you can use the back up interface by two way...you can have the load sharing between link by configuring the load thrashold and other way is when your primary link will get down then it will use the back up secondary link...

when we are talking about the loadsharing then secondary link will atomartically used when the load on the primary link will reach the thrashold configure...

and when we are talking about bakup when primary fail then secondary route will used for the data transfer...

when ever you are talkinga bout the static route then you can configure the static rout with the same AD which are pointing to the both the interface at that time the load balancing will take place and when you configure static route with the diff. AD at that time best AD route will selected and other will use for backup when best AD route lost at that time the secondary route will transfer data...

hope this will help you

rate this post if it helps

regards

Devang

[carl_townshend]

why do we need to use this command then ? surely a static route with different AD would do the same job if both routes were pointing to the interface ?

[devang_etcom]

yes carl static route will work like this...initially the path with the lowest AD will be in routing table and when that route will goes down then the other rout with the large AD will used for the data transfer...

you will find the backup interface in ISDN connectivity...http://www.cisco.com/en/US/tech/tk801/tk379/technologies_configuration_example09186a00800b1148.shtml

hope this will help you

rate this post if it helps

regards

Devang

[carl_townshend]

so what is this command actually doing ? do we still need to point routes out of the backup interface ? and is normal practice to point routes at the local interface or the interface at the other end ?

[devang_etcom]

Command description:

it is just configure the backup interface for the current interface, backup interface is activated when the primary interface goes down or reaches the load specified by the backup load command...by using back up interface command you are pointing out the other interface of the same router ...as the primary link of the router will goes down then the secondary link which is connected with the same router will come up...

hope this helps you

regards

Devang

[carl_townshend]

so do I need to point routes out towards the backup interface still ? and do they need an AD ?

[devang_etcom]

carl noramlly router will try to find out the any alternet path when the primary path or interface down and if it doesnt found any path then it will use the back up path so i dont think so it will need to have other path to point...other wise there is no need to have backup command you can do it by using the static router with different AD and different matric path with routing protocol...

rate this post if it helps you

regards

Devang

[carl_townshend]

Hi thanks for the reply, so are you saying i will not need any routes pointing out this interface ?, can anyone show me an example config with routes ?

[carl_townshend]

Am have just read some more info on this, is it primarily used for routing protocols so it doesnt keep bringing the backup line up ?

[devang_etcom]

carl you will find such a good examples in ISDN configuration technotes or in the refernces like BCRAN book of CCNP as well as in CCIE practical study volume I...

kindly rate the posts

regards

Devang

[carl_townshend]

do people genrally use this command with a routing protocol so it stops it bringing up the line ?

[carl_townshend]

hi all, can anyone give me a definative answer to this ?

thanks all

[amit-singh]

Hi Carl,

We use backup interface command to backup an existing interface which is active and forwarding the traffic. You can use static route or any routing protocol but the route will work only when the interface comes up and it gets installed in the routing table.

You can also use it for load-sharing and when the primary active interface reaches a certain threshold then this interface will become active and start forwarding the traffic.

HTH, let me know if you have doubts on this.

-amit singh

[carl_townshend]

Hi amit

so do i still need to point 2 routes then to the other end ? would the route pointing through the backup interface need a higher cost ? or would 2 normal static routes work as the backup interface is shut down anyway ?