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pinging to remote broadcast address - cant understand the response.

SJ K
Level 5
Level 5

Hi all,

 

As per my earlier thread of pinging to network ID ->

https://supportforums.cisco.com/discussion/12490926/ping-no-response-found-what-does-it-meant

I am now trying to ping to remote broadcast address (from R1 @ 192.168.3.0/24 to R2 @ 192.168.5.0/24)

q1) where does a network address actually resides ?  (e.g. 192.168.5.0 , is it at R2 or R3 or both ?) Why am i able to ping to 192.168.5.0 from R1

q2) on local broadcast 1st, what happen if i send a broadcast from R1 (fe0/0) to 192.168.3.255 ?  Does the broadcast still propagates back to R1 fe0/0 ? on it will be only 1 direction and thats to R2 fe0/0.

q3) I am seeing this responses from 3.2 back to 3.1

355    1002.873686000    192.168.3.1    255.255.255.255    ICMP    114    Echo (ping) request  id=0x0073, seq=1/256, ttl=255 (no response found!)
356    1002.920564000    192.168.3.2    192.168.3.1    ICMP    114    Echo (ping) reply    id=0x0073, seq=1/256, ttl=255
357    1004.889430000    192.168.3.1    255.255.255.255    ICMP    114    Echo (ping) request  id=0x0073, seq=2/512, ttl=255 (no response found!)
358    1004.967556000    192.168.3.2    192.168.3.1    ICMP    114    Echo (ping) reply    id=0x0073, seq=2/512, ttl=255

- why is it 255.255.255.255 and not 192.168.3.255 ? since i am pinging to this subnet (3.0) broadcast ip (3.255)

- why is there a no respond found in the ping request, but there is still a reply coming from 3.2 

----------------------------------------------------------------------------------------------------------------------------------------------------

q4) I have thought routers break up broadcast domain, hence if try to send some information (e.g. ping ) to 192.168.5.255, i should not get any respond. but yet i do and it is coming from 192.168.3.2 !? Why.. (confused)..

R1#ping 192.168.5.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.5.255, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/51/88 ms

Wireshark capture on R2 fe0/0
452    1434.070095000    192.168.3.1    192.168.5.255    ICMP    114    Echo (ping) request  id=0x0075, seq=0/0, ttl=255 (no response found!)
453    1434.132596000    192.168.3.2    192.168.3.1    ICMP    114    Echo (ping) reply    id=0x0075, seq=0/0, ttl=255
454    1434.195100000    192.168.3.1    192.168.5.255    ICMP    114    Echo (ping) request  id=0x0075, seq=1/256, ttl=255 (no response found!)
455    1434.210726000    192.168.3.2    192.168.3.1    ICMP    114    Echo (ping) reply    id=0x0075, seq=1/256, ttl=255

I did not turn on ip direct-broadcast on R2fe0/1 and doing a capture on R2 fe0/1 show that there is no outgoing ping packets from 3.1, but why 3.2 is responding to ping to 5.255  ?

 

Regards,
Noob

 

 

1 Reply 1

SJ K
Level 5
Level 5

Hi all,

 

Any takers :( , is the behavior above normal ? ) to have an interface on 1 side of the router to respond to ping request for another network on another side of the router.

 

Regards,
Noob

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