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LAN Latency/Performance Tuning

I recently added a small remote office to our corporate frame-relay WAN and it has affected the office in some unexpected ways. Prior to this, they operated completely autonomously and their network only consisted of a 3 Mbps DSL connection with a PIX 506e and some Linksys switches. The PIX was their default gateway for all machines on the LAN, including a domain controller, Exchange server, SQL server, etc, etc, etc.

I have replaced all of that with a 2811 router and 3 2950 switches. FA0/1 on the 2811 is now the same IP that the PIX used to have and is now the default gateway and the inside NAT interface. FA0/0 is attached to their DSL modem and is the outside NAT interface, and then S0/0/0 is a T1 CSU/DSU with the frame-relay T1. Routing for our corporate WAN is learned via EIGRP on the frame, and a static default routes sends all non-192.168 (i.e. Internet) bound packets through the NAT pool and out to the DSL modem.

Since doing all this, I am hearing complaints about machines on their network taking much, much longer to communicate back and forth for file/print sharing, longer to login in the morning, etc. I would have thought that all of this traffic, being on the same subnet, would be switched at the 2950's and not even hit the router, but maybe I am wrong. The Windows machines are just hanging sometimes, and it has the look and feel of when Windows is waiting on replies from other machines on the network. I don't know if they are trying to enumerate with Windows machines accessible via the WAN link, or what they are trying to do that is causing them to take 30+ seconds to show the mapped drives in My Computer for instance. None of the mapped drives are outside their subnet or traverse the frame link, etc - shouldn't communication between two machines on the same switch (same VLAN, etc) be pretty much instantaneous? Would this have anything at all to do with the router or is it just a L2 switching issue? I appreciate any ideas.

Super Bronze

Re: LAN Latency/Performance Tuning


You are correct - if all traffic is local it should be fairly quick... I'd start with basic stuff - check your switch ports for errors and for what speed/duplex they're running at (start with a slow client and any servers you have running).

Use this command on each switch:

show int | i duplex|is up,|errors|esc

To get a nice summary...

Let us know how you get on.


Please rate helpful posts.

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

Re: LAN Latency/Performance Tuning


I would backup your assumption that it should be local switching and thus no delays to be expected.

For testing purposes - to rule out the router - you could disconnect the router and check the local performance/latency issues.

Did you check port speed and duplex settings? There are known issues with autonegotiation. Some NICs end up with 10 Mbps half duplex and the switch is at full duplex (or vice versa). Then collisions occur and the throughput is degraded.

My suggestion is to configure fixed speeds and duplex settings on the switches, if possible.

Hope this helps! Please rate all posts.

regards, Martin