Devicename resolution in LMS

Unanswered Question
Feb 6th, 2008

He Experts,

we have around 1000 devices in LMS 2.6

some of them have a hostname configured on the device selve, some are resolved in DNS, some in AD, some has loopback configured, some are in default without hostname or dns or loopback. For the discovery procedure I can select use Reverse DNS Lookup and then Preferred Management IP as Use Loopback Address; Resolve By Name and Resolve By SysName. What will be the best, that I find on the topology device with sensefull name and can switch to ip-address if needed. I do not have the possibility to add all device in DNS now, so what will be the best selection for device discovery setting and do you suggest to build a hosts table on LMS WinServer and work on this to solve names, if yes again what will be the selection in discovery setting combination ?

Danke Gruss Steffen

I have this problem too.
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Joe Clarke Wed, 02/06/2008 - 22:52

Selecting all three options is not a good idea. The way they work is that if use loopback is checked, then Discovery will try to resolve the management IP via a loopback address. If this fails, then no further resolution is attempted. With resolve by name and resolve by sysName, Discovery will first try resolve by sysName, then fallback to resolve by name if that fails.

Ideally, you should pick one algorithm and stick with it. How these algorithms work will also depend on how your name resolution is configured on the server. That is, resolve by loopback will scan all loopbacks on the device. It will pick the operationally up loopback interface with the lowest ifIndex which has an IP address. That IP address will become the management IP. Discovery will look that IP up via the system resolver (then directly in DNS if the system resolver fails). The resulting hostname will be the management hostname.

With resolve by name, Discovery will take the first address by which it learns a device. It will then look that address up to get a hostname. It will then look that hostname up to get another address. This second address will be the management IP for the device, and the aforementioned hostname will be the management hostname.

With resolve by sysName, Discovery will lookup the sysName, and get an IP. That IP will become the management IP for the device. Discovery then looks that IP up, and sets the management hostname to the resulting hostname.

Because of the way these algorithms work, resolve by loopback is the best choice. In fact, using loopbacks for management is a recommended leading practice by Cisco because loopbacks are always up, and all IOS devices can be configured to have the same loopback interface number thus making initial deployments easier (i.e. helps to make a good initial management template for devices).

In your situation, with so many different address scenarios, the local hosts file might make the most sense. Assuming all devices are already configured with loopbacks, you could add the loopback IP with the desired hostname to the hosts file.

steffen.plorin Thu, 02/07/2008 - 04:53

He JClarke,

cool stuff.

Do you explain me the good initial management template for devices, please !

What will be if there are already somme loopbacks, should I configure new one for LMS but what will be with lowest ifindex ?

Each device can have the same loopback interface number but need differnce ip-address, correct ?! Does it mean I need to walk around my 1000 devices and provide a loopback with dedicated ip-address ?

Looking forward for the goooood template !

Danke Gruss Steffen


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