udp broadcast

Hi,

I am testing this command "ip broadcast-address" but seems it doesnt work on serial interface. Can someone please explain on this?

Thanks!

-minh

Comments

  • seems to work on my GNS3 router, what is your test setup or your goal to accomplish with the command?

    R1(config-if)#do sh ver
    Cisco IOS Software, 3700 Software (C3725-ADVENTERPRISEK9-M), Version 12.4(15)T12, RELEASE SOFTWARE (fc3)


    R1#sh ip int | i up|Broadcast
    FastEthernet0/0 is up, line protocol is up
      Broadcast address is 255.255.255.255
      Address determined by setup command
    Serial0/0 is up, line protocol is up
      Broadcast address is 255.255.255.255

      Address determined by setup command


    R1#ping www r 1

    Translating "www"...domain server (255.255.255.255)
    *Mar  1 00:08:09.115: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast

    *Mar  1 00:08:09.119:     UDP src=51326, dst=53
    *Mar  1 00:08:09.119: IP: s=11.11.11.11 (local), d=255.255.255.255 (Serial0/0), len 49, sending broad/multicast
    *Mar  1 00:08:09.123:     UDP src=51326, dst=53
    *Mar  1 00:08:12.123: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast

    *Mar  1 00:08:12.123:     UDP src=51326, dst=53
    *Mar  1 00:08:12.127: IP: s=11.11.11.11 (local), d=255.255.255.255 (Serial0/0), len 49, sending broad/multicast
    *Mar  1 00:08:12.127:     UDP src=51326, dst=53
    *Mar  1 00:08:15.131: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast

    *Mar  1 00:08:15.131:     UDP src=51326, dst=53
    *Mar  1 00:08:15.135: IP: s=11.11.11.11 (local), d=255.255.255.255 (Serial0/0), len 49, sending broad/multicast
    *Mar  1 00:08:15.135:     UDP src=51326, dst=53



    R1(config-if)#do sh ip int | i up|Broadcast
    FastEthernet0/0 is up, line protocol is up
      Broadcast address is 255.255.255.255
      Address determined by setup command
    Serial0/0 is up, line protocol is up
      Broadcast address is 0.0.0.0

      Address determined by setup command


    R1#ping
    *Mar  1 00:09:50.635: %SYS-5-CONFIG_I: Configured from console by console
    R1#ping www r 1

    Translating "www"...domain server (255.255.255.255)

    *Mar  1 00:09:55.483: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast
    *Mar  1 00:09:55.483:     UDP src=57406, dst=53
    *Mar  1 00:09:55.487: IP: s=11.11.11.11 (local), d=0.0.0.0 (Serial0/0), len 49, sending broad/multicast

    *Mar  1 00:09:55.487:     UDP src=57406, dst=53
    *Mar  1 00:09:58.491: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast
    *Mar  1 00:09:58.491:     UDP src=57406, dst=53
    *Mar  1 00:09:58.495: IP: s=11.11.11.11 (local), d=0.0.0.0 (Serial0/0), len 49, sending broad/multicast

    *Mar  1 00:09:58.495:     UDP src=57406, dst=53
    *Mar  1 00:10:01.499: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast
    *Mar  1 00:10:01.499:     UDP src=57406, dst=53



    R1(config-if)#do sh ip int | i up|Broadcast
    FastEthernet0/0 is up, line protocol is up
      Broadcast address is 255.255.255.255
      Address determined by setup command
    Serial0/0 is up, line protocol is up
      Broadcast address is 11.0.0.0

      Address determined by setup command

    R1(config-if)#do ping www r 1

    Translating "www"...domain server (255.255.255.255)
    *Mar  1 00:11:39.127: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast

    *Mar  1 00:11:39.127:     UDP src=51461, dst=53
    *Mar  1 00:11:39.127: IP: s=11.11.11.11 (local), d=11.0.0.0 (Serial0/0), len 49, sending broad/multicast
    *Mar  1 00:11:39.131:     UDP src=51461, dst=53
    *Mar  1 00:11:42.131: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast

    *Mar  1 00:11:42.131:     UDP src=51461, dst=53
    *Mar  1 00:11:42.135: IP: s=11.11.11.11 (local), d=11.0.0.0 (Serial0/0), len 49, sending broad/multicast
    *Mar  1 00:11:42.135:     UDP src=51461, dst=53
    *Mar  1 00:11:45.139: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast

    *Mar  1 00:11:45.143:     UDP src=51461, dst=53
    *Mar  1 00:11:45.143: IP: s=11.11.11.11 (local), d=11.0.0.0 (Serial0/0), len 49, sending broad/multicast
    *Mar  1 00:11:45.147:     UDP src=51461, dst=53



    --
    Garry L. Baker

    "There is no 'patch' for stupidity." - www.sqlsecurity.com



    On Tue, Sep 21, 2010 at 9:44 AM, leminh <[email protected]> wrote:

    Hi,

    I am testing this command "ip broadcast-address" but seems it doesnt work on serial interface. Can someone please explain on this?

    Thanks!

    -minh





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    http://www.internetworkexpert.com



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  • Hi Baker,

    Thanks for the information.

    My setup is: R1 --- R2 ----- R3 --- R4

    R2 & R3 are connected with serial interfaces.

    The rest are connected with fastethernet interfaces

    According to cisco we can convert the general broadcast 255.255.255.255 to directed broadcast by using this command "ip broadcast-address x.x.x.255" where x.x.x is the direct network prefix.

    For fastethernet interfaces, it is working fine.

    However, on serial interfaces, it doesnt seems to work.

    Your output doesnt look like command is effective or else you havent input on the interface itself.

    -minh

     

     

     

  • here is my setup

    R1 <-f0/0-> R2
    R1 <-s0/0-> R2

    and the configuration and the results showing the command does change the broadcast address on the serial interface as before using the command 'ip broadcast address', what am i missing?


    R1#conf t
    Enter configuration commands, one per line.  End with CNTL/Z.
    R1(config)#int s0/0
    R1(config-if)#ip broadcast-address 11.11.11.255
    R1(config-if)#do sh ip int | i up|Broadcast
    FastEthernet0/0 is up, line protocol is up

      Broadcast address is 255.255.255.255
      Address determined by setup command
    Serial0/0 is up, line protocol is up
      Broadcast address is 11.11.11.255
      Address determined by setup command

    R1#sh debug

    *Mar  1 01:28:56.119: %SYS-5-CONFIG_I: Configured from console by console
    Generic IP:
      IP packet debugging is on (detailed)




    R1#ping www r 1

    Translating "www"...domain server (255.255.255.255)

    *Mar  1 01:29:04.515: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast
    *Mar  1 01:29:04.515:     UDP src=60349, dst=53
    *Mar  1 01:29:04.515: IP: s=11.11.11.11 (local), d=11.11.11.255 (Serial0/0), len 49, sending broad/multicast

    *Mar  1 01:29:04.519:     UDP src=60349, dst=53
    *Mar  1 01:29:07.519: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast
    *Mar  1 01:29:07.519:     UDP src=60349, dst=53
    *Mar  1 01:29:07.523: IP: s=11.11.11.11 (local), d=11.11.11.255 (Serial0/0), len 49, sending broad/multicast

    *Mar  1 01:29:07.523:     UDP src=60349, dst=53
    *Mar  1 01:29:10.527: IP: s=1.1.1.1 (local), d=255.255.255.255 (FastEthernet0/0), len 49, sending broad/multicast
    *Mar  1 01:29:10.527:     UDP src=60349, dst=53
    *Mar  1 01:29:10.531: IP: s=11.11.11.11 (local), d=11.11.11.255 (Serial0/0), len 49, sending broad/multicast

    *Mar  1 01:29:10.531:     UDP src=60349, dst=53



    --
    Garry L. Baker

    "There is no 'patch' for stupidity." - www.sqlsecurity.com




    On Tue, Sep 21, 2010 at 11:07 PM, leminh <[email protected]> wrote:

    Hi Baker,

    Thanks for the information.

    My setyp is: R1 --- R2 ----- R3 --- R4

    R2 & R3 are connected with serial interfaces.

    The rest are connected with fastethernet interfaces

    According to cisco we can convert the general broadcast 255.255.255.255 to directed broadcast by using this command "ip broadcast-address x.x.x.255" where x.x.x is the direct network prefix.

    For fastethernet interfaces, it is working fine.

    However, on serial interfaces, it doesnt seems to work.

    Your output doesnt look like command is effective or else you havent input on the interface itself.

     


     
     



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    http://www.internetworkexpert.com



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  • Hi Baker,

    After some testing, I think this command has nothing to do with serial or fastethernet interfaces.

    I tested with this setup: R1 -- R2 -- R3 -- R4

    R4 is dns server

    R3 configure with "ip directed-broadcast" comand on the interfaces toward to R4

    Scenario 1:

    R1 configure with "ip broadcast-address x.x.x.255", where x.x.x is the segment between R3&R4

    nslookup from R1 was successful

    Scenario 2:

    R3 configure with "ip broadcast-address x.x.x.255" on any interfaces, where x.x.x is the segment between R3&R4

    nslookup from R2 was timed out

    The behavior of command "ip broadcast-address" is very hard to understand if compare with "ip helper-address" command.

     

     

     

     

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