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Webcast-Catalyst9k
New Member

Isdn - Backup Interface And Floating Static Conflict

Dear all expert,

Good day.

Kindly help me to answer the ISDN question.

I have a router which using the the IOS -- flash:c3825-advipservicesk9-mz.124-9.T1.bin.

I had configure the #backup interface dialer88 on the serial0/0,

dialer88 is a dialer profile to trigger ISDN.

At the same time, i configure the floating static too.

#ip route 0.0.0.0 0.0.0.0 dialer88.

As i start to test the ISDN, i shut the serial0/0.

The isdn was not triggering or kick in, and i double check the dialer88,

it directly go through disable mode and shut the interface automatic.

Once i remove the #backup interface dialer88 on the serial0/0,

the dialer88 is up and triggering soon.

My question now is .....

Is it IOS issues/bug, or new feature for the IOS to prevent administrative use double backup method -- such as #backup interface with floating static together ??

Please advice.

Many Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Re: Isdn - Backup Interface And Floating Static Conflict

Sae

As I attempted to explain in my first post: the backup interface will activate only in the case of a "failure" of the primary interface. And doing shutdown on the serial is not interpreted as a "failure" by IOS. (the assumption is that if you shut it down you did it on purpose and that is not a failure) To get the backup interface to work you must do something that produces a "failure" of the primary (disconnect the primary, change the encapsulation of the primary, disable keepalive on the remote end of the primary - are all things that I have successfully used to test backup interface).

This behavior is common over all releases of IOS. So it is not anything about this particular router or about the version of code that you are running.

HTH

Rick

7 REPLIES

Re: Isdn - Backup Interface And Floating Static Conflict

Hi,

I don;t think you can use a combination of any of the 3 DDR for the same interface/link.

Check this link http://www.cisco.com/en/US/tech/tk801/tk133/technologies_tech_note09186a008009457d.shtml

Regards,

Dandy

New Member

Re: Isdn - Backup Interface And Floating Static Conflict

Dear Medan,

Thanks for info.

But previously i really did a combination of 2 DDR method -- Backup interface + floating static .. and it is working @@ so i suspect that is it new 12.4 IOS feature/bug fix for using the DDR combination.

Any expert can explain ?

Thanks alot.

Hall of Fame Super Gold

Re: Isdn - Backup Interface And Floating Static Conflict

Sae

It has been my experience using backup interface that IOS has NEVER activated the backup if the primary was shut down. The administrative shut is not considered a failure by IOS and the backup interface is not activated. You need a real failure (something that will take the primary interface to at least protocol down) before the backup interface will activate. This is not a new feature but a long standing restriction.

Also I note that your post refers to the static as a floating static route. But I do not see any administrative distance in the static route that is in the post. As you have configured it the static route will be used any time that interface dialer88 is active and will be removed from the routing table only when the interface goes down. In most implementations of DDR the floating static will be inserted when the normal route (a default route in this case) is removed from the table and the floating static will be removed from the table when the normal route is available again. This is not the behavior that you have configured.

HTH

Rick

Hall of Fame Super Gold

Re: Isdn - Backup Interface And Floating Static Conflict

Following up on my previous post, I believe that if properly configured both backup interface and floating static routes could work. But I believe that it is a less than optimum solution and wonder why you want to use both. If the static default route is configured as a floating static pointing at dialer88 and the regular default route is removed from the table then the floating static would attempt to enter the routing table. But it can not function until the dialer88 interface becomes fully functional and active (based on failure of the serial interface). So it looks to me as if there are two overlapping functions attempting to achieve the same result. Why use both when either one should work?

HTH

Rick

New Member

Re: Isdn - Backup Interface And Floating Static Conflict

Dear Sir,

Thanks for ur guide.

Please see the below scenario.

#ip route 0.0.0.0 0.0.0.0 dialer88 230

#ip route 0.0.0.0 0.0.0.0 58.58.58.58(main serial next hop)

#int serial0/0

#ip address 58.58.58.57 255.255.255.252

#backup interface dialer88

#router bgp 123

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Previously, i shut the serial0/0 down but the dialer88 didn't trigger and i checked the interface dialer88.Later, i found that the dialer88 automatically change to shut down.

After, i remove the #backup interface command on the main interface, the dialer88 immediately change to line protocol up and trigger the ISDN.

So, my question is .....

Why the interface dialer88 will directly change to shut down as main interface down, and after i remove the backup command, dialer88 is up and working ??

Is it IOS -- c3825-advipservicesk9-mz.124-9.T2.bin bug or new features ??

Why i use both when either one should work ?

Testing purpose :)

Dear sir, please advice

Hall of Fame Super Gold

Re: Isdn - Backup Interface And Floating Static Conflict

Sae

As I attempted to explain in my first post: the backup interface will activate only in the case of a "failure" of the primary interface. And doing shutdown on the serial is not interpreted as a "failure" by IOS. (the assumption is that if you shut it down you did it on purpose and that is not a failure) To get the backup interface to work you must do something that produces a "failure" of the primary (disconnect the primary, change the encapsulation of the primary, disable keepalive on the remote end of the primary - are all things that I have successfully used to test backup interface).

This behavior is common over all releases of IOS. So it is not anything about this particular router or about the version of code that you are running.

HTH

Rick

New Member

Re: Isdn - Backup Interface And Floating Static Conflict

Thanks sir ..... i Get it @@

Thanks alot @@

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