Dec
02

You might have a request in the Core Knowledge, Troubleshooting, or the Configuration section to have a Cisco router be able to PING its own Frame-Relay IP address. In this blog post, we will make sure we can accomplish this. Here is the topology that we will use:

ping thyself

The first order of business here is to ensure that R5 can PING the remote device of R3.

Rack9R5#ping 173.9.0.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 173.9.0.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/58/60 ms
Rack9R5#

Excellent! Now let us see if R5 can PING itself. I am hoping this fails or it is going to be my shortest blog post ever! :-p

Rack9R5#ping 173.9.0.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 173.9.0.5, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Rack9R5#

OK. As expected, it does not work. But why? Well, let us debug frame-relay packets and see if we can determine why.

Rack9R5#debug frame-relay packet
Frame Relay packet debugging is on
Rack9R5#ping 173.9.0.5          

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 173.9.0.5, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Rack9R5#
Dec  2 14:05:50.399: Serial0/0/0:Encaps failed--no map entry link 7(IP)
Dec  2 14:05:52.399: Serial0/0/0:Encaps failed--no map entry link 7(IP)
Dec  2 14:05:54.399: Serial0/0/0:Encaps failed--no map entry link 7(IP)
Dec  2 14:05:56.399: Serial0/0/0:Encaps failed--no map entry link 7(IP)
Dec  2 14:05:58.399: Serial0/0/0:Encaps failed--no map entry link 7(IP)
Rack9R5#

There is the answer. Frame-Relay does not know what DLCI to use for this destination IP address. We need to add a Frame-Relay mapping for our own IP address pointing to the DLCI of our neighbor.Let us do that now and then perform our verifications:

Rack9R5#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Rack9R5(config)#int s0/0/0
Rack9R5(config-if)#frame map ip 173.9.0.5 503
Rack9R5(config-if)#do sh run int s0/0/0
Building configuration...

Current configuration : 198 bytes
!
interface Serial0/0/0
 ip address 173.9.0.5 255.255.255.0
 encapsulation frame-relay
 frame-relay map ip 173.9.0.5 503
 frame-relay map ip 173.9.0.3 503 broadcast
 no frame-relay inverse-arp
end

Rack9R5(config-if)#do ping 173.9.0.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 173.9.0.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 116/118/124 ms

Would I engage in this extra configuration unless I was asked to do so in the exam? No way…but at least now we fully understand this under-documented little nuance.


You can leave a response, or trackback from your own site.

12 Responses to “PING Thyself in Frame-Relay”

 
  1. It seems to be a logical answer :) however you teach the way and show the reason an NBMA technology like FR need to be maped with a resolution L3 to L2 address in order to reach each destination it is desired. Excellent… as always!!!

  2. Nick G says:

    Hey this was the QUICKEST tutorial ever. I really enjoy this series, I set up a quick lab and try to figure out before reading, without thinking I said that the frame map ip was missing, in the time it took me to write that I already figured it out.

    That’s a good feeling. Keep em’ coming, I love these little bite sized pieces!

    -Nick

  3. ananth says:

    This is the one thing if you do not know will make a ccie candidate go crazy :)

    Thanks for highlighting this :)

  4. Net_OG says:

    yeah I agree nice and “bite sized”.. Just don’t call it a nugget!

    Maybe we can call them…

    “Tampa Tapas” or a “Reno Oysters”

  5. Olga says:

    Every ping to ip of serial interface first goes on the other end of the link,no matter what encapsulation (traceroute shows it). That’s why in some FR cases (where it’s not p2p) you should have mapping for this ip.

  6. Deepak Arora says:

    I would like to add some little more details for CCIE students.

    1. The self interface ping issue only comes with Frame Relay interfaces those are Multipoint in Nature e.g. Physical FR interface and FR Multipoint Sub interface. Simple reason is that because these interfaces requires Layer 3 to Layer 2 resolution either Statically configured using Frame Relay map statements or by Dynamic means like using Inverse ARP.

    2. Frame Relay point to point subinterfaces do not require any Layer 3 to Layer 2 resolution because logically only one device can be found on the other end of the connection. So if we have situation where we have configured FR point to point subinterfaces (more real world situation), we can actually ping self interfaces without any problem.

    Hope this helps

    regards,
    Deepak Arora

  7. Mbong says:

    I faced a similar scenario once and I failed it. Thanks for bringing the smile to my face.

  8. Ted Pelas Johansson says:

    Why do you want to do like this?

    Just use sub interfaces instead, much better;

    interface Serial0/0/0.1 point-to-point
    ip address 173.9.0.5 255.255.255.0
    frame-relay interface-dlci 20
    end
    !
    interface Serial0/0/0
    no ip address
    encapsulation frame-relay
    frame-relay intf-type dce
    end

  9. Rayees ul hasan says:

    Thanks Very helpful.

  10. EduDeCopas says:

    Hello. I find interesting that when we configure IPv6 addresses, the router is able to ping itself.

    Here is a link that talks about it
    https://supportforums.cisco.com/thread/199833

    Regards,

    Eduardo

 

Leave a Reply

Categories

CCIE Bloggers