Just curious, but when using the LinkSys 10/100 switches, what did they auto-negotiate to? Which speed and which duplex mode?
Did the hub that you installed even understand auto-negotiation? Perhaps it was too old to understand auto-negotiation which was introduced to the IEEE 802.3 specs relatively recently. Of course, the router should have figured this out. (Auto-negotiation is supposed to work even if the other side doens't understand it). But the router might not have been smart enough to do this until you rebooted. In other words, it thought all was fine and didn't bother to renegotiate speed/duplex mode until you rebooted. (See my earlier comment about 10-Mbps link pulses looking similar to auto-negotiation pulses.) In fact, all was fine (sort of) because you could ping. Could it be that after some time elapsed the router interface figured out that there was a duplex mismatch or realized that it was getting a high collision rate (receiving while sending due to the duplex mismatch?) Perhaps STP is smart enough to never leave the blocking state when there is a high collision rate. Anyway, thanks for the helpful case study. Priscilla At 11:42 PM 12/29/01, Ole Drews Jensen wrote: >Chuck, > >At all three offices when I installed these 1720's, I at the same time >installed some new LinkSYS 10/100 switches (the black and blue model). This >worked (works) fine with the 1720 set to auto. > >However, when I replaced the switch, it was with a 3COM hub, and that one is >a 10 mbps. > >I did remove the manual mac config from the FE again, so that was not part >of the solution. > >If you have an old 3COM HUB TP16...(something - I cannot remember the exact >model number), try to set your router in auto sense and connect the hub and >see what happens. > >I guess this is one of these weird situations you come accros sometimes. But >anyway, a speed problem should never cause the STP to go into blocking mode >- those two things doesn't really have anything to do with each other. So, >interesting...... > >Ole > >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > Ole Drews Jensen > Systems Network Manager > CCNP, MCSE, MCP+I > RWR Enterprises, Inc. > [EMAIL PROTECTED] > http://www.RouterChief.com >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > NEED A JOB ??? > http://www.oledrews.com/job >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > >-----Original Message----- >From: Chuck Larrieu [mailto:[EMAIL PROTECTED]] >Sent: Saturday, December 29, 2001 5:14 PM >To: [EMAIL PROTECTED] >Subject: Re: Autosense this ... (add to your knowledgebase) [7:30446] > > >An interesting read, particularly since I am reviewing Kennedy clark's cisco >Lan Switching book prior to reviewing Cat5K and Cat 3920 configuration. > >I am somewhat surprised at both the phenomenon and the concludion. Spanning >tree blocks for particular reasons. > >when you concluded that your configurations were identical at all offices, >does that mean that your port negotiations were set to auto everywhere else? >both on the routers and on the local switches? if so, I would expect to see >similar problems elsewhere. > >is it possible that there was a duplicate mac someplace in another part of >the bridged network, one that was being picked up by STP and interpreted as >a loop? You mention changing macs of interfaces as part of your >experimentation. Are you certain that this process was not part of the >solution? > >To be frank, I'm hard pressed to come up with a reason why the FE port on >the router would go into blocking. I can see that hapening on the serial >port for reasons that have been discussed on this group in the past. I can't >come up with a rationale as to why hard setting of speed and duplex would >make a difference. I suppose one MIGHT conclude that if the port is in full >duplex, the STP process MIGHT see a loop occuring over the two different >wire pairs. that's about the only wild rationale I can come up with. And >that one is really stretching the point / bug / whatever. > >In any case, thanks for the good read. > >Chuck > > >""Ole Drews Jensen"" wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > After a fun evening last night, I have decided not to trust the >autosensing > > on ethernet interfaces anymore. > > > > I was at a branch office where the users could not access the corporate > > network. The router, a 1720 setup as a bridge with the same IP address for > > the FastEthernet as the Serial subinterface, both configured for > > bridge-group 1. It was connected to a 2620 at the corporate office via a > > Fractional Frame Relay connection. > > > > I changed the switch out with an old spare hub I had lying around, and > > connected only one workstation from the local network. After starting the > > router up, I could ping the local workstation, and I could ping devices on > > the corporate network, so both my FastEthernet and Serial interfaces were > > working fine. However, I could not ping anything on the corporate network > > from my workstation, nor could I from a telnet connection to my corporate > > router ping the workstation, so traffic was not being passed through >between > > the interfaces. > > > > That looked like a typical routing problem, but the only problem was that >I > > was not routing, I was bridging, so ????? > > > > I did a "show bridge 1 group" and saw that the FastEthernet was in a > > blocking state by the spanning tree, so something was wrong here. I >cleared > > the arp table on the router and on all other routers and switches. I tried > > to assign a different mac address to the FE interface. I tried a different > > workstation. No matter what I did, it kept being in a blocking state. > > > > I went in and did a "bridge-group 1 spanning-disabled" on the interface, >and > > it changed to forwarding state, but I could still not pass traffic >through. > > > > This is when I called TAC, but after I guided them through to a telnet > > connection to my routers, they decided after three hours that something > > weird was going on with the router, and they did an RMA for a replacement > > unit. > > > > However, I decided to continue my troubleshooting, because I hate to give > > up. I reconfigured everything, I tried to create a bridge-group 2 instead, >I > > forced it into IP routing, and back off it again, but no matter what, it > > kept going into blocking mode (I had removed the spanning-disabled command > > again at that time). > > > > That's when it hit me to try and force the speed on the interface. It was >in > > AUTO, and my switch had been auto 10/100, but my hub was only 10. I >changed > > it from auto to 10 and power cycled the router. PLING!!! Now it started up > > and after the listening and learning, it went in forwarding state, and I > > could now ping through my router, and I could connect my workstation to >the > > corporate network. > > > > What makes this strange is that I can apparently use my FastEthernet > > interface from the router even though the speed is wrong, but the STP >see's > > this and blocks the interface for switched traffic. WEIRD!!!!! > > > > Read the entire case study here: > > > > http://www.RouterChief.com/CaseStudies/1.htm > > > > Ole > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Ole Drews Jensen > > Systems Network Manager > > CCNP, MCSE, MCP+I > > RWR Enterprises, Inc. > > [EMAIL PROTECTED] > > http://www.RouterChief.com > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > NEED A JOB ??? > > http://www.oledrews.com/job > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30559&t=30446 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
