Deepak N wrote: > > HI All > I have simple configuration of HDLC connected back to back. > If i give ip unnumbered at one end and the static ip address at > the other end, I cant ping the either end. But when i give show > ip int brief, it shows the line and protocol are up. > If i give ip unnumbered at both ends, now i am able to ping > either end. > could anybody help me out in this. > > Regards > Deepak
This stuff is impossible to remember. Everytime I think I have it committed to memory, I wind up back at: http://www.cisco.com/en/US/tech/tk648/tk365/technologies_tech_note09186a0080094e8d.shtml An interesting excerpt: "The only real disadvantage that the unnumbered interface suffers from is that it is unavailable for remote testing and management." But more importantly: When unnumbered is used, a route that is learned via the unnumbered interace is placed into the routing table using the unnumbered _interface_ it came in on as opposed to the next hop IP. If the next hop IP were to be used, problems would arrise because tit isn't directly attached (everything eventually has to boil down to a directly attached interface so the packet can be offloaded). The next hop IP is on the back side of the distant-end unnumbered interface. Unnumbered was meant to conserve address space on p-t-p serial links. It was assumed that both ends would implement it. In the case of a numbered interface, the "use the interface instead of next hop IP" logic isn't implemented. Thus, the router inserts the next hop (which is behind the unnumbered inteface on the other end). The problem, of course, is that the next hop isn't directly attached. And no special logic has been implemented to compensate. I think I got that right. Read the link and see if it adds up. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=62194&t=62134 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
