Creating Loopback interface on production routers

Answered Question
Jul 30th, 2007

Hello everyone,

I have two questions:

What are the repercussions of configuring loopback interfaces on routers running in full production with various routing protocol i.e. EIGRP & OSPF.

If there are, is there a way that we may avoid those issues and still be able to configure virutal interfaces on Cisco devices without impacting business.

Looking forward to your prompt respones.

Regards,

Hashsham

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Correct Answer by Edison Ortiz about 9 years 5 months ago

A well configured OSPF network, would have a router-id under the OSPF process to avoid this kind of issues.

Correct Answer by balajitvk about 9 years 5 months ago

Hi,

Creating the loopback interface won't make any impact on the ongoing traffic..... It won't make any difference until you advertise in any of routing protocol.... Even advertising this, will provide way for other routers to reach this thro. that loopback ip.... Nothing much to do on the ongoing traffic until you make any wrong configuration.

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Correct Answer
balajitvk Mon, 07/30/2007 - 07:11

Hi,

Creating the loopback interface won't make any impact on the ongoing traffic..... It won't make any difference until you advertise in any of routing protocol.... Even advertising this, will provide way for other routers to reach this thro. that loopback ip.... Nothing much to do on the ongoing traffic until you make any wrong configuration.

Rgs.

hashsham1 Mon, 07/30/2007 - 07:43

Thank you very much for the response. However I have the following concern.

1- In case of OSPF, DR and selection of BDR is dependent on Loopback address. If a router comes to have a loopback that it never had, then IP addresses for loopback addresses will have to be carefully chosen to avoid any impact on the current set up.

Otherwise, there will be production issues...right?

Regards,

Hashsham

Correct Answer
Edison Ortiz Mon, 07/30/2007 - 07:54

A well configured OSPF network, would have a router-id under the OSPF process to avoid this kind of issues.

royalblues Tue, 07/31/2007 - 03:47

I agree with Edison that configuring a router-id is the best possible way to implement and avoid such issues.

When a router comes online it always checks for an existing DR and BDR and only goes into an election mode if it doesn't find one. So creating a loopback interface would not disrupt the production traffic.

However if the ospf process restarts for some reason, all the checks are now applied taking the loopback interface into consideration

HTH

Narayan

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