Discovery - Best Practice

Question

Greetings,
I was wondering how most engineers approach Discovery, especially on larger networks.  I'm not interested in the methods so much but more in how you "define" a valid discovery range.  I think on most networks, for each subnet there will be one or two ip addresses for network devices and the rest of the range will be servers, workstations, etc.  Since you can't do an include and an exclude on the filters how do you make it such that your network devices are discovered but servers, firewalls, etc. aren't?  Do you manually "include" every device in the filter?  Use the SysObjectID somehow?  Is there a way to exclude devices that you don't want to repeatedly discover without using the exclude filter?
The ideal outcome would be to discover everything relevant and nothing that wasn't but also retain the ability to discover new devices that might be plugged into the network at a later time.  How do most engineers handle this issue?  Anyone know of a good document that covers this subject?  Thanks in advance!
George          

Answer 1

So far this has always been quite a bit of searching, mapping, etc to find what is in place. And this is a manual exercise :-|
Selecting devices to manage is usually best done on systemobjectid. Most management system have such list of vendor OID. If you have many vendors you list will be longer. Sometimes naming conventions indicate router or switch but it is not 100% reliable.
Choosing the management address is a bit harder. I would never use a physical interface however, always a virtual. I first want to establish a device is reachable, after that retrieve the state of the interfaces.
What I tend to do is try and find out about IP ranges reserved for management. Next would be to try and map between the system-name or DNS-name of a device and the desired IP address.
With this info you can then 'discover' the network and based on the lookup of system-name or DNS-name retrieve the IP you need.
In an ideal world you would be able to get a list of IP addresses of all devices in your network combined with the interface names and select an address from there. After all it is not uncommon that a specific VLAN is used as a management VLAN, however even though this info can be gathered simply from mib2,  I'm not aware of any product out there, that can do this.
LMS for instance, can select the lowest lo0 loopback (if it is available) as a management interface.
Sometimes info is already present in IP address reservation systems, sometimes in access control systems, sometimes it is already for a large part in a DNS.
If 'nothing' is in place I would suggest to define a loopback/VLAN interface on every device. Of course this will add to your routing tables. But you can then take the management VLAN to separate QOS class giving it the priority you feel it needs.
I tend to keep a subnet per site and tried to allow for subnet summarization of subnet's on the WAN, but in the MPLS backbones this is often not really a requirement anymore.if your network topology is a star then it may still be worthwhile
Just a little brainstorm,...
Cheers,
Michel