mirror of
https://github.com/OpenVPN/openvpn3.git
synced 2024-09-20 12:12:15 +02:00
6608878d57
Adds mssfix support including optional
transport overhead. Some code has been ported
from openvpn2.
mssfix sets MSS option in TCP SYN to
a calculated value which guarantees that
size of UDP/TCP packet (which may or may not
include headers, see below) encapsulating
TCP segments won't exceed mssfix value.
If mssfix is used with optional "mtu" parameter,
then IP and UDP/TCP headers are also taken into account.
It is set in config like this:
mssfix 1300 mtu
Signed-off-by: Lev Stipakov <lev@openvpn.net>
91 lines
2.3 KiB
C++
91 lines
2.3 KiB
C++
// OpenVPN -- An application to securely tunnel IP networks
|
|
// over a single port, with support for SSL/TLS-based
|
|
// session authentication and key exchange,
|
|
// packet encryption, packet authentication, and
|
|
// packet compression.
|
|
//
|
|
// Copyright (C) 2012-2017 OpenVPN Inc.
|
|
//
|
|
// This program is free software: you can redistribute it and/or modify
|
|
// it under the terms of the GNU Affero General Public License Version 3
|
|
// as published by the Free Software Foundation.
|
|
//
|
|
// This program is distributed in the hope that it will be useful,
|
|
// but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
// GNU Affero General Public License for more details.
|
|
//
|
|
// You should have received a copy of the GNU Affero General Public License
|
|
// along with this program in the COPYING file.
|
|
// If not, see <http://www.gnu.org/licenses/>.
|
|
|
|
#pragma once
|
|
|
|
#include <openvpn/common/endian.hpp>
|
|
#include <openvpn/ip/ipcommon.hpp>
|
|
|
|
namespace openvpn {
|
|
|
|
#pragma pack(push)
|
|
#pragma pack(1)
|
|
|
|
struct TCPHeader {
|
|
static unsigned int length(const std::uint8_t doff_res)
|
|
{
|
|
return ((doff_res) & 0xF0) >> 2;
|
|
}
|
|
|
|
std::uint16_t source;
|
|
std::uint16_t dest;
|
|
std::uint32_t seq;
|
|
std::uint32_t ack_seq;
|
|
std::uint8_t doff_res;
|
|
std::uint8_t flags;
|
|
std::uint16_t window;
|
|
std::uint16_t check;
|
|
std::uint16_t urgent_p;
|
|
|
|
// helper enum to parse options in TCP header
|
|
enum {
|
|
OPT_EOL = 0,
|
|
OPT_NOP = 1,
|
|
OPT_MAXSEG = 2,
|
|
OPTLEN_MAXSEG = 4
|
|
};
|
|
|
|
enum {
|
|
FLAG_SYN = 1 << 1
|
|
};
|
|
};
|
|
|
|
#pragma pack(pop)
|
|
|
|
/*
|
|
* The following routine is used to update an
|
|
* internet checksum. "acc" is a 32-bit
|
|
* accumulation of all the changes to the
|
|
* checksum (adding in old 16-bit words and
|
|
* subtracting out new words), and "cksum"
|
|
* is the checksum value to be updated.
|
|
*/
|
|
inline void tcp_adjust_checksum(int acc, std::uint16_t& cksum)
|
|
{
|
|
int _acc = acc;
|
|
_acc += cksum;
|
|
if (_acc < 0)
|
|
{
|
|
_acc = -_acc;
|
|
_acc = (_acc >> 16) + (_acc & 0xffff);
|
|
_acc += _acc >> 16;
|
|
cksum = (uint16_t)~_acc;
|
|
}
|
|
else
|
|
{
|
|
_acc = (_acc >> 16) + (_acc & 0xffff);
|
|
_acc += _acc >> 16;
|
|
cksum = (uint16_t)_acc;
|
|
}
|
|
}
|
|
}
|
|
|