Ethernet and Flow Control
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Posted by ChrisW on June 30, 2006, 4:34 pm
Please log in for more thread options Which "Flow Control" nic setting would get the best performance on a lan with Gigabit lan? Disabled or generate & respond? Why? Thanks in advance, ChrisW | ||||||||||||||||||||||||||||||||||||||||
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Posted by glen herrmannsfeldt on June 30, 2006, 9:12 pm
Please log in for more thread options ChrisW wrote: It depends on what else it is connected to. -- glen | ||||||||||||||||||||||||||||||||||||||||
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Posted by Wrolf on July 2, 2006, 11:32 pm
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ChrisW wrote: > Which "Flow Control" nic setting would get the best performance on a
> lan with Gigabit lan? Disabled or generate & respond? Why? > > Thanks in advance, In general, I would use the default for that NIC. The feature is pretty much useless .In much the same way as an ICMP source quench, a PAUSE frame really does not give enough information to do anything good with in a working network, and can easily go to the wrong device and cause more problems. Class of Service and Quality of Service, e.g. Diff-Serv and 802.3p are really the way to go. If push came to shove, I guess I would set generate and respond. But that is with great hesitation, since the better solution in a network with so much traffic and so little bandwidth might be to rely on proven methods like TCP window size and other congestion control methods. If you need 802.3x PAUSE frames switch to switch, then your network probably already collapsed. Switch to switch (to me) is a don't care. Wrolf | ||||||||||||||||||||||||||||||||||||||||
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Posted by anoop on July 3, 2006, 1:59 pm
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Wrolf wrote: > Class of Service and Quality of Service, e.g. Diff-Serv and 802.3p are
> really the way to go. I think you mean 802.1p. Anoop | ||||||||||||||||||||||||||||||||||||||||
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Posted by anoop on July 3, 2006, 1:57 pm
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ChrisW wrote: > Which "Flow Control" nic setting would get the best performance on a
> lan with Gigabit lan? Disabled or generate & respond? Why? The general thinking is that it makes sense to enable 802.3x flow control only on "edge" ports; i.e. those ports that are connected directly to end-stations. Enabling 802.3x on an inter-switch link is usually not a good idea because of the following. - It causes head-of-line blocking (slows traffic that isn't necessarily causing congestion). - It causes higher burstiness which is not desireable for certain applications such as VoIP. - It is not sensitive to the priority of frames. The transmission of all frames is stalled for the duration of the pause on the link. This last point is particularly significant for control protocols such as LACP (used for link aggregation), STP/RSTP/MSTP, and routing protocol packets. Very long pause durations could result in instability in the network because the control protocols may assume (incorrectly) that they have lost the adjacency. Anoop | ||||||||||||||||||||||||||||||||||||||||
> lan with Gigabit lan? Disabled or generate & respond? Why?