Priscilla, In your reply below, you're saying that "A half-duplex Ethernet interface (whether on a bridge, switch, router, server, or PC) monitors for a collision while sending. If a collision occurs, the interface (I assume you're talking about the interface on the router/bridge) re-transmits the frame". So this tells me that a router/bridge Ethernet interface is able to re-transmit a frame. Correct? Then why do you state in the next paragraph "The CCIE tests expect you to know that neither a bridge nor router re-transmits if a frame experiences a bit error or gets lost somehow". Could you please clarify further? Thank you!
Shawn K. > -----Original Message----- > From: Priscilla Oppenheimer [SMTP:[EMAIL PROTECTED]] > Sent: Tuesday, May 07, 2002 12:16 AM > To: [EMAIL PROTECTED] > Subject: Re: Router/Bridge re-transmit frames? [7:43459] > > Regardless of whether a router is configured for bridging or routing, it > must send an Ethernet frame successfully, without a collision. A > half-duplex Ethernet interface (whether on a bridge, switch, router, > server, or PC) monitors for a collision while sending. If a collision > occurs, the interface retransmits the frame. This happens at the Media > Access Layer, and has to do with accessing the medium successfully and > nothing more. The station listens while sending and retransmits if a > collision occurs. That's basic CSMA/CD. Every Ethernet interface (that is > in half-duplex mode) must do CSMA/CD. > > This doesn't mean that a router or bridge retransmits in most cases. The > CCIE tests expect you to know that neither a bridge nor a router > retransmits if a frame experiences a bit error or gets lost somehow. > Retransmitting is up to the end station. A recipient bridge or router > doesn't send back any sort of message to a sending bridge or router to > report a problem. It's up to the end station to know that a packet didn't > get ACKed. A router could send an ICMP message. In general, those go back > to the end station though. An intermediate router has no way to know if a > problem occurred and retransmit. > > A few other exceptions to the rule that a router doesn't retransmit are > Binary Synchronous Communication Protocol (BISYNC) and LAPB. > > Priscilla > > At 11:27 PM 5/6/02, Kaminski, Shawn G wrote: > >I've always known routers to "route" and bridges to "learn, filter, > forward, > >and flood". A co-worker said that if a router is configured with > transparent > >bridging, it can re-transmit a frame. He said that he heard this > somewhere. > >I'm pretty sure he's wrong because this just isn't something that a > >router/bridge is meant to do. I also searched CCO but came up > empty-handed. > > > >For example, say you have two segments connected to a router; one segment > >off of e0 and one segment off of e1. If a host on the e0 segment sends a > >frame to a host on the e1 segment and a collision occurs on the e1 > segment > >before reaching the destination host, then I believe that the host on e0 > is > >responsible for re-transmitting the frame, not the router/bridge. > > > >Has anyone heard of a router configured with transparent bridging > >re-transmitting frames? I just can't see how this could happen. However, > >I've seen stranger things happen, so I just wanted to get the opinions of > >others on this group. > > > >Shawn K. > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=43483&t=43459 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
