ping 8000 bytes in size not making it

Unanswered Question
Feb 13th, 2009

Is there any way to let this size of packet go through on an interface.

when I ping and make the packet 8000 it fails.

Any advice would be great

I have this problem too.
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Paolo Bevilacqua Fri, 02/13/2009 - 10:58

What's the point ? That is like sending 4 packet and an half as fragments, and expect the router to reassemble them, thing that it never does or is expected to do. Only ping to larger MTU and if you're really in an pinging mood, use sweeping sizes.

Paolo Bevilacqua Fri, 02/13/2009 - 11:48

That will fail on numerous types of interface that don't support large MTU, like frame-relay, ethernet, and many others.

cisco24x7 Fri, 02/13/2009 - 12:49

"That will fail on numerous types of interface that don't support large MTU, like frame-relay, ethernet, and many others."

I like to know where you get this information from. This is a 9000 bytes

ping across a Cisco 7140 router:

[[email protected]]# ping -s 9000 -c 5 98.174.21.130

PING 98.174.21.130 (98.174.21.130) 9000(9028) bytes of data.

9008 bytes from 98.174.21.130: icmp_seq=0 ttl=255 time=7.49 ms

9008 bytes from 98.174.21.130: icmp_seq=1 ttl=255 time=7.47 ms

9008 bytes from 98.174.21.130: icmp_seq=2 ttl=255 time=7.52 ms

9008 bytes from 98.174.21.130: icmp_seq=3 ttl=255 time=6.37 ms

9008 bytes from 98.174.21.130: icmp_seq=4 ttl=255 time=6.36 ms

--- 98.174.21.130 ping statistics ---

5 packets transmitted, 5 received, 0% packet loss, time 4042ms

rtt min/avg/max/mdev = 6.366/7.045/7.522/0.563 ms, pipe 2

[[email protected]]#

Paolo Bevilacqua Fri, 02/13/2009 - 13:00

I was responding to the suggestion of setting an arbitrary larger MTU on the interface, it is not possible to do so, hence the command fails.

With regard to the ability of the router of reassembling ping packets, your 7140 appears to do that well, other platforms /IOS could not, yet that does not indicate a problem whatsoever.

cisco24x7 Fri, 02/13/2009 - 13:34

It works on the C3640 platforms as well.

The ping goes across the Cisco 3640 and

7140 and it still works:

C3640#ping 98.174.21.134 source f1/0 size 9000 repeat 10

Type escape sequence to abort.

Sending 10, 9000-byte ICMP Echos to 98.174.21.134, timeout is 2 seconds:

Packet sent with a source address of 129.174.1.2

!!!!!!!!!!

Success rate is 100 percent (10/10), round-trip min/avg/max = 12/14/20 ms

C3640#

Mohamed Sobair Fri, 02/13/2009 - 13:32

Hi,

Ping with 8000 byte packet size causes a router to fragments the packets.

The default MTU on Cisco router interface is 1500, The Fragmentation can cause delays, and if the delay is larger than 2 seconds (default time out) you will see . instead of !

This doesnt necessarily means the packet is not transmitted at all, it just means there is no reply within those 2 seconds.

HTH

Mohamed

Paolo Bevilacqua Fri, 02/13/2009 - 13:38

Good point, but to fail due to timeout, the interface must be really, really slow.

More likely the failure is due to some internal buffer that is insufficient.

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