----- Original Message ----- From: "Lennert Buytenhek" <[EMAIL PROTECTED]> To: "Mathew McKernan" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Thursday, December 13, 2001 11:17 PM Subject: Re: [Bridge] Buffering of packets
> > On Thu, Dec 13, 2001 at 10:22:50PM +1100, Mathew McKernan wrote: > > > Hey all, > > Hi there, > > > > We currently are having some network problems across our microwave link. We > > have 2 seperate buildings linked by this microwave link. Both LANs are 100MBps > > and the link is 10MBps. In an attempt to stop excess data from flowing across > > the link we placed a bridge between the LAN and radio at both buildings. > > Unfortunetly both of these bridges are only 10MBps. So data is flying at > > 100MBps to the switch that each bridge is on and comes to a grinding halt and > > trickles through the bridge to the radio onto the other building. Because there > > is a high amount of traffic about twice a day the bridge "locks-up". i.e. > > doesnt forward packets and its CPU locks up. We have swapped the bridges and no > > success. On closer inspection we found that its buffer was overflowing > > What bridge were you using for this? What underlying hardware, > operating system, network cards? How did you diagnose that 'its buffer > was overflowing'? Magnum 3000, about 6 years old. They were sitting on a shelf doing nothing and the hub that the link was on died. It was a quick fix that stuck. I am not entirly sure what OS etc. But i guessed it overflowed because it stopped responding and its clocking led stopped dead. Also as it locked up it put spourous data out its RS 232 managment port. I am no expert here, but it was a guess that was some how "educated". Its a 2 port bridge with BNC, AUI and TP on each port. It only runs at 10MBps. The microwave link is interfaced via AUI. The switch is 10/100MBps. Even though the switch sees the bridge as 10Mbps it still dumps the data quickly. > > > > So I was reading on the internet and found the Linux Ethernet Bridge project. I > > have build a box to replace the bridge that keeps on "locking up". The box has > > 2 LAN cards that are both 100MBps. We are hoping that this box will not crash > > and not drop packets because its buffer overflows. Can anyone confirm that the > > Linux box will hold the data and eventually get it across the link? > > Heh, well I can assure you that there is no code in the linux ethernet > bridge code to actively lock up the machine under load ;) Under no > circumstance should active network equipment 'lock up' due to high load. Sounds good to me :) > > I'm not exactly sure what you mean with your question. If you are asking > whether linux ever drops packets, I can assure you that it will. If you > are bridging from 100Mbit to 10Mbit, it takes ten times longer to transmit > the data than to receive it, so if insist that no packets be dropped, even > if you put the 100Mbit under load for a day, you will need 10 days worth > of 10Mbit buffering capacity in the bridge, which is about a terabyte. I know we dont run our LAN that hard :P, but i see what your saying. The Magnum bridges were made about 6 years ago when the designers didnt think about 100MBps to be used in the future on LANs. > > It's generally acceptable to drop traffic under load. The end hosts are > supposed to detect this and retransmit. It will not benefit performance > if this happens, but things should keep working. > > > cheers, > Lennert Thanks for your help Mathew _______________________________________________ Bridge mailing list [EMAIL PROTECTED] http://www.math.leidenuniv.nl/mailman/listinfo/bridge
