Larry Letterman wrote: > > Most likely the previous 10/half interface on the switch and > the router > were not > linked at the same speed/duplex or the other router had an > issue with > the setting.
No, the switch and router were set to the same thing, which was 10 Mbps half duplex, if you read his messages. He was using a 2500 router. Those routers predate the full duplex standard. In fact they may predate 100 Mbps also. He had no choice but to upgrade the router, which he did. He was seeing lots of collisions, including excessive collisions where the frame got dropped because even after 15 retries it encountered a collision. Collisions are normal in shared (half-duplex) Ehternet, but excessive collisions are not. Collisions are caused by the stations on the shared link simultaneously sending. Excessive collisions are due to a shortage of capacity. One fix to the problem is to increase the capacity. By jumping 10-fold from 10 Mbps to 100 Mbps, the risk of collisions, especially excessive collisions, goes way down. Since each frame takes 1/10th the amount of time to send, the odds that some other station is sending when another station transmits (or retransmits) go way down. Increasing capacity used to be the only way we could upgrade an Ethernet network. Then the full-duplex standard came about. It can only be used on a point-to-point link where each side has its own dedicated transmit path. In other words, it's no longer shared Ethernet. There's no need to sense carrier to see if anyone else is sending, because there isn't anyone else. It's not multiple access. Receiving while you're sening is legitimate, so there's no need to check for collisions. It's no longer CSMA/CD. Of course the collision rate goes down. Collisions really have no meaning in this environment. If there are collisions, then there's probably a duplex mismatch. So, anyway, he improved matters in two ways: upgrading the capacity and moving to full duplex. I just wanted to add this theory discussion. It's not right to say (as someone else did) that collisions are "caused by" a half-duplex setting. Collisions are caused by two stations sending at once, which tends to happen more and more frequently when there's not enough capacity to support the sending behavior of the nodes on the shared network. To fix the problem, you can increase capacity or you can make the network not shared by connecting just two devices and using full duplex. _______________________________ Priscilla Oppenheimer www.troubleshootingnetworks.com www.priscilla.com > > To be safe I would set the switch port and the router interface > to > 100/full or 10/full > and there should be no issues then. > > and yes, the fast ethernet in the 26XX/36XX routers are a > better > solution..... > > Larry Letterman > Cisco IT-LAN , San Jose > > Cliff Cliff wrote: > > >Today, We are put 3660 router to their end, having > Fastethernet card, and > >connected to their switch. > > > >They change their switch port as following: > > > >interface FastEthernet0/14 > >load-interval 30 > >duplex full > > > >so far, after observe serveral hours, there is no collision as > well as not > >error message in our router. > > > >So, what's wrong? Is the fastethernet is better? or previous > setting that I > >have is wrong? > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58480&t=58389 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
