I am having a strange problem. We have two sites connected by two 100Mbs lines.
In order to bypass complications raised by propagating our routes over MLPS it was decided
to use two GRE tunnels to connect the two sites.
On both sides of the WAN links we have 1Gbs for all our worskations and servers but the connecting lines are running, as mentioned above, at 100Mbs each.
The CPU usage, Memory Usage for the routers connected at each end of the two lines (2 pairs of C2821) are OK, both variables under 50%. The line is not used at full capacity, we do experience short spikes for traffic values but nothing to worry us and to explain what I am going to say below.
The problem we have is that our users are reporting, and I have tested that myself, dropped SSH sessions or dropped RDP sessions which run accros these two lines.
The GRE tunnel interfaces on each router present output queue drops and these can not be correlated with any spikes for traffic values or CPU loads observed on this routers at the same time with the measuring the output drops rate via SNMP. Moreover the drops seem to happen randomly...
By my knowledge a router should display output queues drops only when it deals with congestion and that should be also revealed by the traffic values measured at that moment when the output drops appear.
Has anybody experienced something like this? Does anybody have any ideea what else could cause these drops? I should also mention that I am seeing output queue drops on the switches connected behind these 2821 roauters (C3750 stacks at one end and 4506 at the other end).
These could also be caused by workstations or servers trying to adjust their TCP window size but...this shouldn't cause SSH or RDP session drops
Thanks in advance for any suggestion