Routers unable to ping each other

sharat11sharat11
in CCIE Routing & Switching Technical

Hi, this may sound like a silly question..

I connected 2 routers via serial.

R1# int s0/0

        Ip address 1.1.1.1/30

        No shut

R2# int s0/0

         Ip address 1.1.1.3/24

         No shut

In this scenario according to me R1 should be able to ping R2 as 1.1.1.3 is broadcast Ip for R1.

But it's not pinging.. can anyone elaborate on this.

Regards,

Sharat

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Comments

  • Hari.sapkotaHari.sapkota ✭✭

    Hi Sharat,

    You are sending the ip directed broadcast in 1.1.1.0/30 network. So, only the valid hosts that belong to the particular network respond for the same. A broadcast address can never be the source of a packet. Therefore, your ping won't work in this case.

    If you configured 1.1.1.2/24 instead of .3 and send the ping from R1, it would get the response as shown below:

    R1#ping 1.1.1.3

    Type escape sequence to abort.

    Sending 5, 100-byte ICMP Echos to 1.1.1.3, timeout is 2 seconds:

    Reply to request 0 from 1.1.1.2, 1 ms

    Reply to request 1 from 1.1.1.2, 1 ms

    Reply to request 2 from 1.1.1.2, 1 ms

    Hope this helps!
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  • sharat11sharat11
    Hi Hari,
     
    Thanks for the input.
    Please see the debug result which I see from both routers..
     
    R1# ping 1.1.1.3
    Type escape sequence to abort.

    Sending 5, 100-byte ICMP Echos to 1.1.1.3, timeout is 2 seconds:
    *Mar  1 00:02:59.155: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 100, sending broad/multicast.
    *Mar  1 00:03:01.239: IP: tableid=0, s=1.1.1.3 (FastEthernet0/0), d=1.1.1.1 (FastEthernet0/0), routed via RIB

     
     
    R2# *Mar  1 00:15:54.795: IP: s=1.1.1.1 (FastEthernet0/0), d=255.255.255.255, len 100, rcvd 2
    *Mar  1 00:15:54.795: ICMP: echo reply sent, src 1.1.1.3, dst 1.1.1.1
    *Mar  1 00:15:54.799: IP: tableid=0, s=1.1.1.3 (local), d=1.1.1.1 (FastEthernet0/0), routed via FIB

     
    I am getting echo replies from R2 on R1 where the source ip is 1.1.1.3 which is the broadcast ip for R1, is that why I am unable to see successful ping result.
     
    Regards,
    Sharat



    On Mon, Oct 21, 2013 at 3:31 PM, Hari.sapkota <[email protected]> wrote:

    Hi Sharat,

    You are sending the ip directed broadcast in 1.1.1.0/30 network. So, only the valid hosts that belong to the particular network respond for the same. A broadcast address can never be the source of a packet. Therefore, your ping won't work in this case.

    If you configured 1.1.1.2/24 instead of .3 and send the ping from R1, it would get the response as shown below:

    R1#ping 1.1.1.3

    Type escape sequence to abort.

    Sending 5, 100-byte ICMP Echos to 1.1.1.3, timeout is 2 seconds:

    Reply to request 0 from 1.1.1.2, 1 ms

    Reply to request 1 from 1.1.1.2, 1 ms

    Reply to request 2 from 1.1.1.2, 1 ms

    Hope this helps!



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  • Hari.sapkotaHari.sapkota ✭✭

    Yes, 1.1.1.3/24 is not a broadcast address for R2 but its a broadcast for R1. So, it could be the reason of ping failure. :)

    Good luck

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