Re: Strange throughput anomaly: gateway fast, behind gateway slow

From: Ralf Gerlich
Date: Fri May 06 2005 - 02:18:31 EST


On Thu, May 05, 2005 at 01:34:58PM -0500, Jason Clark wrote:
> Silly question, but have you checked your speed/duplex settings on the lan
> side of the gateway to make sure you dont have a mismatch with your
> switch/hub?

Not that silly, though it's not the solution :-/ The gateway has only one NIC. The DSL modem and the rest of the network are on the same hub - which is probably not the cleanest solution but it had worked the last 2-3 years. Therefore a mismatch is impossible - or am I misunderstanding your question?

I already thought that one additional difference between the gateway and the hosts "behind" the gateway is that when downloading on the gateway the data is at its destination already when it is received by the gateway from the DSL modem. In the other case - downloading on a host behind the gateway - the data has to be retransmitted from the gateway to the target using the same ethernet line as the connection to the DSL modem. Yet the increased delays of 80-100ms are between sending the ACK of the last packet out to the DSL modem and getting the next packet from the DSL modem. There is no transmission from or to the client in between.

I have an additional NIC lying around here - an old 3C509B - which I could put in the gateway to check whether separating the gateway-DSL-connection from the gateway-LAN-connection helps, but as your question implies that may add more unknown variables.

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