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Posted by Robert Emert on June 5, 2006, 9:24 am
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The reason is very simple: the router doesn't know to which DLCI should
map your own IP address.
For that reason you are receiving encapsulation failed error message.
Larry Jones wrote:
>>To successfully ping your own interface address, another router must send
>>back the ICMP echoes and the echo replies.
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>>I have seen this...you can't ping the local FR interface, you can from a
>>machine behind the router ping the interface.....
>>
>>
>>JB www.helpwithcisco.com
>>
>>
>>>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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