Full duplex problem with servers

[vveen]

We have 8 offices connected with leased lines. Each router (3640 with 10baseT ethernet mod, IOS 12.2.7) is connected to a 3com switch with full-duplex. This configuration is maintained at all offices. I encounter severe communication problems with netware and nt-servers. I found documents that advise to switch the routers and servers to half duplex in stead of full. After I did this communication problems disappear quickly.

In my opinion a server and router should always run at full duplex. The "solution" to turn back to half is unacceptable I think.

Do you have an advise or opinion about this. Your help would be appreciated.

Valentijn van Veen

[csthomas]

Do the underlying comm links actually support full duplex, or are they half duplex? If the latter, then if you run the end networks in full duplex, you're going to have to have enough buffering so that you don't drop packets before the comm link can process them. In this case, it's probably better to buffer in the servers by making them hdx.

[vveen]

the leased lines are serial connections with hdlc encapsulation. According to my information this connection is full duplex. I enclosed a sh contr s1/2 output.

#sh contr s1/2

CD2430 Slot 1, Port 2, Controller 0, Channel 2, Revision 18

Channel mode is synchronous serial

idb 0x611AF368, buffer size 1524, V.35 DTE cable

output omitted....

Is there a way to find out if the wan connection is full duplex?

Thanks again.

[rfroom]

It sounds like you may some Duplex Mismatches, read the following document that describes how to properly configure half-duplex and full-duplex connections.

www.cisco.com/warp/customer/473/46.html

[vveen]

In the original situation all nic's and switch port's were hard coded to full-duplex. My serial lines are full-duplex, I confirmed. The sh int ethernet0/0 did not show any crc, runts or other problems. However, the connection from one server to another is full-duplex and still the problem exists. In the first place I thought netware was the problem. But connection problems with nt servers pointed me to another cause. When switching to half-duplex (hard-coded in every connection)all problems disappear. In the link you send me there is no connection made with 10baseT full-duplex. Could this be the problem. i.e. can you run at full-duplex with a 10Mbps network module in a 3640?

Thanks again.

[msjouw]

An older 10mb card for the 3640 will NOT support full duplex unless you have a minimum of 12.1.7 or higher loaded. This feature was not supported in older versions of the ios. You will not be able to set duplex on this interface if the feature is not supported. When setting full duplex on servers do make sure that they really do so, for we found often that NT servers indicate they are running Full but are actually still running half. When fixing the switch port OR the server make sure you fix the other side also.

Further to that there is no direct connection between a serial link and an ethernet link. Each interface is treated seperately.

Regards, Maarten Sjouw.

[joke]

Is the 3Com switch a 10/100 switch or a 10 mb switch? If it is 10 only it may only be capable of half duplex operation.

[jeff]

I have experienced this problem many, many times with various NICs and Switches. Check to see if the switch and other side are both set for Auto Negotiation. If both sides are set to Auto Negotiate, invariably this will cause problems.

The solution is to set one side only (switch) for Auto Negotiate, and set the other side to "fixed" parameters, i.e. Full Duplex 100. Better yet, turn off Auto Negotiate entirely.

See Cisco's FAQ on Ethernet and Auto Negotiation:

http://www.cisco.com/warp/public/473/3.html