every 2nd echo-request malformed when ping -s >4067

[Harald Schmalzbauer]

 Hello,

while checking new mtu9k-setup, I discovered that ping has some odd
behaviour.
If I use payloadsize > 4067, every 2nd icmp-echo-request seems to be
malformed:

ping -s 4068 -D 10.5.49.65

1st: 12:21:09.048447 IP 10.5.49.126 > 10.5.49.65: ICMP echo request, id
46597, seq 0, length 4076
        0x0000:  4500 1000 0f2d 4000 4001 a507 0a05 317e

2nd: 12:21:10.052891 IP 10.5.49.126 > 10.5.49.65: icmp
        0x0000:  4500 1000 0f2d 0040 4001 e4c7 0a05 317e

3rd: 12:21:11.062900 IP 10.5.49.126 > 10.5.49.65: ICMP echo request, id
46597, seq 2, length 4076
        0x0000:  4500 1000 0f2d 4000 4001 a507 0a05 317e

4th: 12:21:12.072915 IP 10.5.49.126 > 10.5.49.65: icmp
        0x0000:  4500 1000 0f2d 0040 4001 e4c7 0a05 317e

5th: 12:21:13.082900 IP 10.5.49.126 > 10.5.49.65: ICMP echo request, id
46597, seq 4, length 4076
        0x0000:  4500 1000 0f2d 4000 4001 a507 0a05 317e

When payload is 4076, outgoing _every_ outgoing request begins with
    4500 xxxx xxxx 4000 4001,
while above we see every second request starting with
    4500 xxxx xxxx 0040 4001.

Does anybody know header composing off pat? Haven't seen these bits for
quiet some time...

Thanks,

-Harry

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