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With reference to this question and to ASIO libary, I would like to know what is the maximum size of ICMP v6 reply packet. I'm using ASIO library to listen for and receive ICMPv6 packets, but I don't know what size of buffer to use in order to prevent buffer over flow. I'm confused by IPv6 supporting extension headers.

Ex code:

asio::streambuf replyBuffer;
replyBuffer.consume(replyBuffer.size());
size_t length = icmpV6Socket->receive(replyBuffer.prepare(65536) );
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Marcus Frenkel
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1 Answers1

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One of the great features of Boost.Asio's buffers is that they provide protection against buffer overruns. Boost.Asio's buffers pair together a handle to the actual memory and the size. Thus, as long as the size is properly set or deduced, then Boost.Asio operations will not produce buffer overruns.

Nevertheless, the details for ICMPv6 sizes are as follows. IPv6 Header is 40 bytes, and reserves 2 bytes to represent the Payload Length. Thus, the max payload for IPv6, including extension headers, is 65,535. This differs from IPv4, where the Total Length included the header itself. The ICMPv6 Echo Reply header is 8 bytes.

Therefore:

  • The maximum IPv6 packet is 65,575 bytes (max payload of 65,535 + header of 40).
  • The maximum IPv6 payload is 65,535 bytes.
  • The maximum ICMPv6 Echo Reply body is 65,527 bytes. (max payload of 65,535 - ICMPv6 Echo Reply Header of 8).
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Tanner Sansbury
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  • With reference to my code example, if I use: icmpV6Socket->receive(replyBuffer.prepare(65575) ) there is no chance of overflow in replyBuffer right? – Marcus Frenkel Mar 16 '13 at 02:48
  • @MarcusFrenkel: If you use [`streambuf::prepare()`](http://www.boost.org/doc/libs/1_53_0/doc/html/boost_asio/reference/basic_streambuf/prepare.html) with _any_ value, it will not cause a buffer overrun. Therefore, yes. Using 65575 will not cause a buffer overrun. – Tanner Sansbury Mar 16 '13 at 03:12