Overview of scenerio...A complete Cisco network. 2950s used for access switches and 3550 for each building core with VLANs define at that core to route the VLANs (one VLAN per floor). If I do a throughput test with Chariot or iperf from port to port on same switch and same VLAN, I get about 86Mb on 100Mb link. No problem. That is probably the best that can be expected. When I run a test to different VLANs on the same 2950 switch connected back to the 3550 that has the VLANs defined I get only about 15 - 20 Mb throughput. I have done extensive packet captures and found that on the slower throughput I have what I think are excessive retransmissions and duplicate ACK packets (about every ten packets). The configs on the switches are pretty simple and straight forward. The amount of "other" traffic on the links is practically non existant. Does using the 3550 as a layer 3 switching lose that much capability in throughput? I thought the concept to layer 3 switching was route once, switch many so why would this affect throughput? Any thoughts are appreciated.
Nat
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check the link between the 2900 and 3550 for collisions. Try hard-coding the speed and duplex to 100 Full Duplex on each switch on the port connecting the 2 switches. You shouldn't always trust they they will auto-negotiate the right setting, even if they are both Cisco switches.
Clear the port counters, transfer some data, and check the interface statisitics looking for errors/collisions.
OK. I should have included more info but was pressed for time when posting. The swiches are coonnected via MM fiber thru the GBIC ports. THe ports are hardcoded as trunk ports with proper configurations (according to Cisco site) and show no errors of any kind. I upgraded the software late Friday to 12.1(22).EA3 on the 2950 switch and 12.1(22)EA4 on the 3550 switch (I think, I might have them backwards). No change in throughput via different VLANs using Chariot or iperf.
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by: Another-DanPosted on 2005-09-30 at 02:38:18ID: 14990711
I have had a similar problem with 2950's moving from switch to switch with a crossover cable. The probelm was cured because the ios's were incompatible! So upgraded both switchches to the same revision and it suddenly started performing.
Good luck