Curious wrote: > > Open Question!!!! > How do we detect the source of collision, i am experiencing > alot of > collision on my LAN, which consisit of 10 Base T HUBS and > 10/100 Switches, i > am seeing alot of collision, but i dont know where is a Source, > If some one > knows how to detect the source of collsion will be great help > for me > !!!!!!!!!!!!!!!!!!!!!!!!!!! >
Hello Curious, It takes two to tango. Seriously, a collision means two or more stations sent at the same time, so it's difficult to identify a single source of the collisions. The stations involved sense the carrier, see that it is free, and start transmitting. Their frames collide somewhere in the middle. The senders send their jam and then stop sending. They back off and retransmit. It can be very difficult to determine which stations were involved in the collision because the senders stop prematurely, usually before they have sent an entire source address. An Ethernet frame starts with preamble, dest address, source address, and then length or type. On most networks, all the collisions happen within the preamble and dest address. Note that collisions are normal on shared Ethernet. If you have a lot of collisions, then you should start dividing up your collision domain with switches. In fact, not only is that a good design approach, it's really the only way to troubleshoot also. You have to use a divide-and-conquer approach and divide up the network until you find the culprits. I see that someone suggested using a protocol analyzer. You could capture all the fragments (runts), which are frames that are too short, usually due to a collision. But these frames may not have a source address, as mentioned. And not only that, you may be just seeing the victims of the problem, not necessarily the perpetrators. To determine which stations are most likely to need a lot of bandwidth (and were possibly involved in lots of collisions), you could use a protocol analyzer to determine who are the biggest senders. Actually, the stations that are most involved in collisions are the ones that send the most often, which is not necessarily the biggest bandwidth hogs, but usually it is. Because most networks these days are already micro-segmented (with small collision domains), the most likely cause of high collisions is a duplex mismatch. All the stations that are connected to hubs must be set to half duplex. Any station that is connected point-to-point to a switch can be set to full duplex as long as the switch port is also set to full duplex. IEEE 802.3 is supposed to make all this work automatically. The autonegotiation feature should make sure that you don't have any mismatches. Even if you connect to an old hub that predates autonegotiation, the workstation is supposed to recognize this. 10Base-T hubs send pulses that the workstation should recognize as coming from a half-duplex hub, causing the workstation to use half duplex. Unfortunately, autonegotiation fails a lot of the time. This could result in you having a workstation on a shared network that is set to full duplex, which would wreak havoc. It would send whenever it wanted, rather than doing carrier sense first. But that station will be very hard to find. How big is your network? Can you manually check devices? HTH, sorry it was so long-winded! ;-) ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=48847&t=48830 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
