Since I switched everyone over to using the MikroTik router, I've been getting complaints from all of our IM users that they are getting large numbers of disconnect/reconnects through the day.

When I set up the Mikrotik FW, I also set up a DSL connection in addition to our T1. At first I had it set to simply send all traffic through the DSL line. When people started complaining about IM, I thought it might have something to do with the DSL line, so I added a Mangle rule in the prerouting chain that maked any traffic with a destination port of 5190 with a routing mark of IM. I then added a route:

Destination: 0.0.0.0/0
Gateway: our gate way
Interface: T1
Routing Mark: IM

to route IM traffic through the T1. I'm not sure if this made much of a difference.

What else can I try to do to stabilize our IM connections??

Have a look at this page:

http://www.chebucto.ns.ca/~rakerman/port-table.html

Port 5190 is only for AIM / AOL messenger. MSN uses port 1863 and a few others.

If this doesn't help, post your NAT and ROUTES to this forum and we'll see what we can do.

What I would suggest, is to setup queue tree's, and give priority to IM's and VoIP etc. In some cases you could also have a MSS problem. Try not to change your MSS over your DSL link. Some secure sites won't work when your MSS setting is incorrect.