Network Health Monitoring Program

Any advice for me on a simple to use program that would monitor the health (avail bandwidth, load, retransmissions, etc.) of a small network?

[code:1]
Big Network eth0
|
|
|
-- --------
| 1|----| switch |
-- --------
| |
-- | |
| 2|------ |
-- |
|
-- |
| 3|--------
--
[/code:1]

Simplified diagram shows what the configuration is. If I run Ethereal on Box 1 and listen on eth1, I will be able to log all traffic going from any machie on the subnet to/from the big network, as well as from any machine on the subnet to/from Box 1. However I will miss the data between Box 2 and Box 3 since the switch will keep that data away from Box 1.

Okay, option 1: Find another tool that will log and analyze data like Ethereal, only set it up to somehow monitor the health of the hardware switch.

Option 2: Run another network monitor program on Box 2 (don't think I can use Ethereal, since Boxes 2 and 3 are QNX while Box 1 is Linux) and somehow line the data up with what was acquired on Box 1.

Option 3: Just assume that whatever bandwith is left over after running Ethereal and logging it, is always available to Boxes 2 and 3.

I really want to see some graphs and summaries of all the data that is being handled by the switch, and not just Box 1.

Any advice? Thanks in advance.

If you switch is Cisco catalyst you can SPAN or MONITOR a port, group of ports or a VLAN to another
port. Not familiar with HP or 3Com but I would guess if the switch is a "manageable" switch capable of
VLANs then it would have a similiar feature. You could run tcpdump on Machine 2 and 3 and then read
the capture files with ethereal, won't be real-time but better than nothing. Addtionally there is a tool
called ettercap that may help. http://www.sans.org/rr/whitepapers/networkdevs/244.php

Todd Magers
toddmagers@gmail.com