Re: Can't ping local FR interface

To successfully ping your own interface address, another router must send

> back the ICMP echoes and the echo replies. >I have seen this...you can't ping the local FR interface, you can from a > machine behind the router ping the interface..... > > > JB
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> >> I ran across a Cisco's FAQ on the subject, unfortunately I got more >> confused from reading the explanation as why one can't ping a local >> frame-relay interface (the setup is similar to the one posted in >> another thread, I pasted it to the end of the email), below is the >> excerpt from Cisco: >> >> "A: You cannot ping your own IP address on a multipoint Frame Relay >> interface. To make a ping successful on a serial interface, an >> Internet Control Message Protocol (ICMP) echo packet must be sent, and >> an ICMP echo reply packet must be received. Pings to your own >> interface address are successful on point-to-point subinterfaces or >> high-level data link control (HDLC) links because the router on the >> other side of the link returns the ICMP echo and echo reply packets. >> The same principle applies with multipoint (sub)interfaces. To >> successfully ping your own interface address, another router must send >> back the ICMP echoes and the echo replies. Because multipoint >> interfaces can have multiple destinations, the router must have >> mapping for every destination. Because mapping is not made for our >> interface address to point toward other routers, which would send our >> ICMP packets back, the router does not have any layer-two to >> layer-three mapping for its own address and does not know how to >> encapsulate the packet. An encapsulation failure results." >> >> My question is why should the router at the other end come into play >> when I ping a local frame-relay interface. Cisco seem to indicate >> that the ping somehow goes out on the wire (or the PVC) to the router >> at the other end and comes back? Is this a limitation on Cisco router >> in implementing serial interface or am I missing something here? Any >> insight would be greatly appreciated. >> >> John >> >> ----------------------- referenced configuration setup >> -------------------- >> R1 (s0/0)--------(s0/0)R2(s0/1)--------(s0/0)R3 >> >> R2 is configured as FR switch with no ip addresses set (interfaces are >> dce >> with clockrate) >> >> R1 is: >> interface serial 0/0 >> ip address 172.16.0.1 255.255.255.0 >> encapsulation frame-relay >> >> R3 is: >> interface serial 0/0 >> ip address 172.16.0.2 255.255.255.0 >> encapsulation frame-relay >> >> mappings are: >> -on R1 >> Serial0/0 (up): ip 172.16.0.2 dlci 203(0xCB,0x30B0), dynamic, >> broadcast,, status defined, active >> -on R3: >> Serial0/0 (up): ip 172.16.0.1 dlci 302(0x12E,0x48E0), dynamic, >> broadcast,, status defined, active >> >> it looks ok. I can ping from R1 to R3 and (of course) from R3 to R1, >> but I can't ping from R1 it's own serial interface and from R3 its >> serial >> interface. >> >> debug frame-relay packet >> -------------------------- >> Type escape sequence to abort. >> Sending 5, 100-byte ICMP Echos to 172.16.0.2, timeout is 2 seconds: >> >> 02:25:04: Serial0/0:Encaps failed--no map entry link 7(IP). >> 02:25:06: Serial0/0:Encaps failed--no map entry link 7(IP). >> 02:25:08: Serial0/0:Encaps failed--no map entry link 7(IP). >> 02:25:10: Serial0/0:Encaps failed--no map entry link 7(IP). >> 02:25:12: Serial0/0:Encaps failed--no map entry link 7(IP). >> >> Why can't I ping routers own serial interface???? >> > >
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Larry Jones
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Robert Emert

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