Questions about network discovery

[Darth Jed]

I have a few questions for all of you that have done this before, but especially for Doug Schulze and Aleck Lin.

1. According to the wiki, network discovery will scan the MID server's gateway router for its routing table and then use that table to identify other routers. After that, the process repeats across the network until all network devices and networks have been identified. The network discovery will not scan every IP address across the network to identify network devices. Is this correct?

2. I was asked if there was a way to throttle the network discovery to limit the bandwidth needs. I haven't found a way, except to limit the number of threads the MID server can use. Is there another way? Is it even necessary to throttle the network discovery?

3. My network team is concerned about taking down remote sites with network discovery and normal discovery scans due to the remote sites having limited bandwidth. We have multiple MID servers located around the country in areas that reduce the distance between the server and that scan's target device. The team has read both of the following articles and still has concerns. We're planning a test scan of a network device at a remote site to evaluate the bandwidth usage. Do you have any other ideas or information that will help put their concerns to rest?

http://wiki.servicenow.com/index.php?title=Deploying_Multiple_MID_Servers#gsc.tab=0

http://wiki.servicenow.com/index.php?title=Discovery_Resource_Utilization#gsc.tab=0

John Edwards

Kansas City Southern

[doug_schulze]

John,

First I have to ask why do you need to do a networks discovery?   I ask because ive rarely seen that used since it first came out for Discovery Patient zero.  

For reference to those reading that may not be aware of what Network discovery does... We have that in there so that our friends out there that have NO idea how many ranges or subnets they need to discover as was Patient zero's need.   So as you describe you would point a networks discovery at your core or seed routers where we will ask for all the vlans that the device managed and who they shared that information with (OSPF), we would then go to those peers and ask the same questions spidering around the networks till we exhausted the number of devices we learned about.   We would then populate the IP Networks table so that you could create range sets to be used in a proper configuration items discovery.   Think of going around town asking all the post offices what neighborhoods they deliver mail to.

So John, you might be able to extrapolate that a network discovery is no different than any other discovery other then its actually doing less and more targeted than a "normal" configuration items discovery. The only concern you should have is about utilization on the devices.   See when we go ask for that routing information , by RFC law those devices must resort their tables before providing an answer, kinda like your office is a mess but you know where everything is, the moment the boss comes in and asks for that report you have to put everything in order before you hand it over...Well this can cause a utilization spike and if the device is already at 90+% well..

So bottom line if you already have your IP Ranges and subnets theres really no reason to do a Network discovery...Is that the case?

[Darth Jed]

Thanks for the quick reply, Doug. I've been considering a network discovery because I've seen the number of ranges we have. I'm concerned about the amount of time it would take to enter all the ranges or even just to import all the ranges. The tool that contains the ranges outputs them as CSV files, one for each subnet and each file contains every IP address in the range. As I see it, I'd save a lot of time if network discovery created all the ranges for me.

[doug_schulze · Accepted solution]

John,

Id look to importing the ranges over doing a network discovery, its actually really easy, quick and gives you much more control over your range sets then what a network discovery can provide. Primarily your range set will be locked down to a router/l3 switch over you defining the groups...

[Darth Jed]

Doug, I'm going to continue the conversation offline with you, if you don't mind. I don't want to publicly share all the details of that hurdle.