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Adding Loopback to CMM question

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Feb 2nd, 2009
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I added a loopback to the CMM we have in our 6500. As there is no routing protocol will I need to put an ip secondary on the default g/w?

<br />Of course even though the logs dont reflect, is there any reason not to put a loopback in this? As I am now being blamed for some voice issues at a remote site. Thanks

Update, well it seems that the original configuration did not have a "bind" statement for the CCM to use. So when I put in the loopback, all calls started trying to register to the loopback.

Can someone clarify why?

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Nicholas Matthews Mon, 02/02/2009 - 18:28
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For most voice protocols, the interface chosen is the 'closest interface'. Generally, you can a 'show ip route x.x.x.x' and see which interface it will use to access.

A lot of routing protocols will use the highest loopback value as the Router ID / source. Offhand, I can't think of a voice situation that uses this; not to say it's not possible. If you're sending/receiving routing protocol information on that interface it's very likely the router will choose that interface.

If you have a router with more than one interface, you should have a bind command.

Loopbacks are handy for using IP addresses that are used for management and are easier to remember. They're used more often used for devices with multiple IP addresses so that they can be managed and reached with a single address. If your device (like a CMM) only has a single IP address, it will offer much less service.



rtuttle Tue, 02/03/2009 - 06:48
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I'm familiar with the loopback stuff, and this is a module in a 6513. What is funny is there is no routing protocol just connected and the default static to the gateway.

Since we are in a multi customer setup, I use public ip's as the mgmt so as not to step in rfc1918 address duplicates between customers.

More than anything what I was looking for is a comment that cisco doesnt recommend using loopbacks on the cmm as they say not to do it for access points. Though both will let you configure one.


Nicholas Matthews Tue, 02/03/2009 - 07:06
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I don't think there is a recommendation to not have loopbacks. Rather, there isn't much reason to have a loopback on a CMM since it would be a single interface - single IP address device.


rtuttle Tue, 02/03/2009 - 07:23
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What was found by the onsite folks was when I put in the loopback and activated. Apparently all incoming calls were registering with the loopback address (or trying) instead of the interface. I assume this is related to your statement of highest/lowest vlan/loopback interface. Ok, this said apparently a bind statement was needed to ensure the bind to the correct interface. I just can't find documentation on this aspect.



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