On Tue, 2006-03-14 at 10:41 -0500, Dan Williams wrote: > On Tue, 2006-03-14 at 10:24 -0500, Darren Albers wrote: > > I just tried to use NM and a Cisco 2950 switch without portfast > > enabled, this resulted in NetworkManager assigning me a 169.x address. > > > > When I tried this on a 3550 it went from Blocking to Forwarding a lot > > quicker so NM worked fine and anyone who sets up a switch for user > > access is probably going to enable portfast so this may not be a big > > deal and might only affect a small number of users who probably work > > in a Datacenter and know to just click on NM and have it reconnect to > > the wired. > > > > I don't know of any way for NM to detect that a switch is going > > through all the STP checks so maybe the ethernet timeout could be > > increased a little? In theory, NetworkManager could listen for Spanning Tree BPDUs to determine whether Spanning Tree was in use on the port. > In this case my switch went from blocking to > > forwarding about 3 seconds after NM gave up and assigned me a 169 > > address so it should not need to be much longer... > > What's the situation here? NM only cares if the machine's ethernet card > has a link or not, which is reported by the driver for the card itself. > Once the driver reports that it has a link, NM will attempt to acquire a > DHCP address on that port. > > Are you saying that the switch takes a long time to actually start > passing traffic from the machine on which NM is running, even though the > port is active? Yes, when the full Spanning Tree protocol is in use on a port, it can take 15 seconds from the time that the switch detects link on the port and the time that the switch will start to forward data frames. The Cisco "spanning-tree portfast" modifies the Spanning Tree protocol so that the port goes immediately from the blocking state to the forwarding state (bypassing the listening and learning states). Other switch vendors have similar methods of disabling/modifying Spanning Tree to avoid this problem. Jeff
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