Larry Letterman wrote: > > In most cases you will only re-write the source mac address > when traversing > across a L3 device.
I don't think that's so. A host will have an ARP cache entry for its gateway. That would be the destination MAC. The source MAC would be that of the sending host itself. Using its own ARP cache, the gateway would re-write both the source and destination MAC if the destination was, in fact, directly attached to (or reachable via) another Ethernet interface. If not, and the packet needed to cross some serial WAN link, both MACs would simply be stripped off. Every L3 device strips off source and dest. MAC at ingress. Whether or not a new source and dest. MAC is encapsulated around the IP packet depends on whether or not the destination is reachable via another Ethernet interface. > If you go across a layer 2 network, all > the mac address's > would typically be part of the same broadcast domain and not > need to be changed. > > If you go across a T1 or Frame it will still be mapped to or > have an assigned IP Address > that constitutes a layer 3 hop and write its mac address in > the frame. > > However if I am wrong here, Priscilla or Howard or Chuck > will let me know...:) > > Larry Letterman > Network Engineer > Cisco Systems > > > ----- Original Message ----- > From: "Cisco Newbie" > To: > Sent: Friday, January 31, 2003 11:42 AM > Subject: RE: MAC Address [7:62251] > > > > First, thanks for all that responded. One clarification > that I need address > > is the following: > > > > If I cross a L3 router and the outgoing interface is > something other than > > Ethernet, will the L2 frame show a new MAC address? In > other words, if my > > outgoing interface is say T1 PPP or even a dial-up, should > I be seeing a new > > MAC address? > > > > Is it only when I cross a L3 device AND my outgoing > interface is a share > > medium like Ethernet that a new MAC address will be placed > on the frame? > > > > Thanks. > > > > > > > > --------------------------------- > > Do you Yahoo!? > > Yahoo! Mail Plus - Powerful. Affordable. Sign up now > [EMAIL PROTECTED] > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=62354&t=62251 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
