Hi Les, hi Paul,
I don't think there is so much mysterie about discovery. Maybe I'm wrong but
here is the way I think it works with most tools (without seed-File, that is
tool-specific):
o read the arp-cache of your local machine your software is running on
In most cases you now you have at least the IP-address of the
default-gateway discovered. If your Network is not switched you'll have more
adresses.
Loop for each new IP-address
o try to read the interface-table with snmp from this IP-address
If you have snmp-access this will give you a list of connected
IP-networks you now can draw on your map
o try to read the ARP-table from this IP-address
this will give you more new IP-addresses to work on
o try to read the routing-tables from this IP-address
this might give you even more addresses to work on
end loop
The seedfile can help to
- set up addresses that have to be checked to speed up discovery
- prevent other addresses from beeing checked
- ... (see manual)
It is easy to see why discovery sometime fails:
- you have no snmp-access to a gateway due to incorrect communities
- you have no snmp-access to a gateway due to access-lists or firewalls
- you have devices without snmp (are there still some out there?)
- some ip-addresses are very silent and are no longer in an arp-table
(some tools try to avoid this doing a ping to all possible IP-addresses,
but just think of a Class A - network...)
- routing problems: you discover IP-addresses in some arp-tables but
you are unable to reach them
- one of the most common problems is that you use name resolution
and this may take very long if
the addresses can't be resolved. I observed a case where the second
or third nameserver in hierarchy didn't answer and there seemd to be a
timeout-problem which caused netmon to wait forever,
so there were no more status changes on the map
(wasn't too bad, erverything stayed green forever ;-)).
Well, I hope I am not too wrong with this and didn't forget too much, but from
this model I could solve or at least find all problems regarding discovery so
far (well, there is this problem with firewalls discussed lately...).
Happy discovering
Michael Seibold
Gmünder Ersatzkasse GEK
>>> lesdickert@hotmail.com 15.03.2001 04.22 Uhr >>>
I think you're going to find that, like
all other products that do network
discovery, NetView's discovery process
is a trade secret. Translation: even
the developers don't understand it.
I think you can bet ARP is involved though.
Les Dickert
Verisign Consulting
>From: "Paul Maine Jr." <paulm@msicc.com>
>Reply-To: IBM NetView Discussion <nv-l@tkg.com>
>To: "Netview List (E-mail)" <nv-l@tkg.com>
>Subject: [NV-L] NetView Discovery and ARP
>Date: Wed, 14 Mar 2001 14:33:40 -0600
>
>Does NetView use ARP as part of the automated discovery process? If so, how
>does it use ARP? I have read conflicting statements in the Tivoli
>documentation.
>
>Thank You
>Paul
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