Telnet connection lags when routed
I have several clients that use telnet to connect to an application server. If the clients are on the same subnet as the server, everything is ok. If I move the clients to a different subnet and route them through a Linux server (different network cards or same network card with virtual eth's, it makes no different), there are intermittent hick-ups, when the cursor seems to stall for a quarter or a half of second. The situation is not singular to one server, we use this setup in many headquarters and it's always the same. The servers are Slackware, but vary from 10.2 to 12.1, iptables varies from 1.3.5 to 1.4.0 and iproute2 varies from ss050330 to ss060323, with different hardware configurations.
For example, if I connect and then keep a key pressed (let's say "a"), it outputs: 15 a's, half second pause, 20 a's, quarter second pause, 10 a's, half second pause, a.s.o.
I really don't know how to handle this problem or even where to start with it. Any pointers would really be appreciated.
This situation might happen with other connection types, not only telnet, but this is where it's most pressing and easy to verify.
I've also made some checks and there's no problem with the clients or the server, it all happens in the router. Also, no errors or dropped packets on the interfaces. It all happens over the LAN, so no third party network which could cause this.