Re: Anyone seeing ping corruption?

[Masataka Ohta <mohta () necom830 hpcl titech ac jp>]

Bjorn Mork wrote:

> > No, an ICMP echo reply does not include the entire request packets
>
> RFC792:
>        The data received in the echo message must be returned in the echo
>        reply message.

RFC792:

Echo or Echo Reply Message

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Identifier          |        Sequence Number        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Data ...
   +-+-+-+-+-


The data excludes IP and ICMP header and is not "the entire
request packets".

Once an echo request packet is reassembled, which may cause
buffer overflow with poor implementations, you only have to
rewrite type, checksum and IP header to construct echo reply
without copying data, which is what BSD kernel is doing.

                                                Masataka Ohta