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Diffstat (limited to 'src/openvpn/mtu.h')
| -rw-r--r-- | src/openvpn/mtu.h | 308 |
1 files changed, 308 insertions, 0 deletions
diff --git a/src/openvpn/mtu.h b/src/openvpn/mtu.h new file mode 100644 index 0000000..29ec21f --- /dev/null +++ b/src/openvpn/mtu.h @@ -0,0 +1,308 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program (see the file COPYING included with this + * distribution); if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#ifndef MTU_H +#define MTU_H + +#include "buffer.h" + +/* + * + * Packet maninipulation routes such as encrypt, decrypt, compress, decompress + * are passed a frame buffer that looks like this: + * + * [extra_frame bytes] [mtu bytes] [extra_frame_bytes] [compression overflow bytes] + * ^ + * Pointer passed to function points here so that routine + * can make use of extra_frame bytes before pointer + * to prepend headers, etc. + * + * extra_frame bytes is large enough for all encryption related overhead. + * + * mtu bytes will be the MTU size set in the ifconfig statement that configures + * the TUN or TAP device such as: + * + * ifconfig $1 10.1.0.2 pointopoint 10.1.0.1 mtu 1450 + * + * Compression overflow bytes is the worst-case size expansion that would be + * expected if we tried to compress mtu + extra_frame bytes of uncompressible data. + */ + +/* + * Standard ethernet MTU + */ +#define ETHERNET_MTU 1500 + +/* + * It is a fatal error if mtu is less than + * this value for tun device. + */ +#define TUN_MTU_MIN 100 + +/* + * Default MTU of network over which tunnel data will pass by TCP/UDP. + */ +#define LINK_MTU_DEFAULT 1500 + +/* + * Default MTU of tunnel device. + */ +#define TUN_MTU_DEFAULT 1500 + +/* + * MTU Defaults for TAP devices + */ +#define TAP_MTU_EXTRA_DEFAULT 32 + +/* + * Default MSSFIX value, used for reducing TCP MTU size + */ +#define MSSFIX_DEFAULT 1450 + +/* + * Alignment of payload data such as IP packet or + * ethernet frame. + */ +#define PAYLOAD_ALIGN 4 + + +/**************************************************************************/ +/** + * Packet geometry parameters. + */ +struct frame { + int link_mtu; /**< Maximum packet size to be sent over + * the external network interface. */ + + int link_mtu_dynamic; /**< Dynamic MTU value for the external + * network interface. */ + + int extra_frame; /**< Maximum number of bytes that all + * processing steps together could add. + * @code + * frame.link_mtu = "socket MTU" - extra_frame; + * @endcode + */ + + int extra_buffer; /**< Maximum number of bytes that + * processing steps could expand the + * internal work buffer. + * + * This is used by the \link compression + * Data Channel Compression + * module\endlink to give enough working + * space for worst-case expansion of + * incompressible content. */ + + int extra_tun; /**< Maximum number of bytes in excess of + * the tun/tap MTU that might be read + * from or written to the virtual + * tun/tap network interface. */ + + int extra_link; /**< Maximum number of bytes in excess of + * external network interface's MTU that + * might be read from or written to it. */ + + /* + * Alignment control + */ +# define FRAME_HEADROOM_MARKER_DECRYPT (1<<0) +# define FRAME_HEADROOM_MARKER_FRAGMENT (1<<1) +# define FRAME_HEADROOM_MARKER_READ_LINK (1<<2) +# define FRAME_HEADROOM_MARKER_READ_STREAM (1<<3) + unsigned int align_flags; + int align_adjust; +}; + +/* Routines which read struct frame should use the macros below */ + +/* + * Overhead added to packet payload due to encapsulation + */ +#define EXTRA_FRAME(f) ((f)->extra_frame) + +/* + * Delta between tun payload size and final TCP/UDP datagram size + * (not including extra_link additions) + */ +#define TUN_LINK_DELTA(f) ((f)->extra_frame + (f)->extra_tun) + +/* + * This is the size to "ifconfig" the tun or tap device. + */ +#define TUN_MTU_SIZE(f) ((f)->link_mtu - TUN_LINK_DELTA(f)) +#define TUN_MTU_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic - TUN_LINK_DELTA(f)) + +/* + * This is the maximum packet size that we need to be able to + * read from or write to a tun or tap device. For example, + * a tap device ifconfiged to an MTU of 1200 might actually want + * to return a packet size of 1214 on a read(). + */ +#define PAYLOAD_SIZE(f) ((f)->link_mtu - (f)->extra_frame) +#define PAYLOAD_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic - (f)->extra_frame) + +/* + * Max size of a payload packet after encryption, compression, etc. + * overhead is added. + */ +#define EXPANDED_SIZE(f) ((f)->link_mtu) +#define EXPANDED_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic) +#define EXPANDED_SIZE_MIN(f) (TUN_MTU_MIN + TUN_LINK_DELTA(f)) + +/* + * These values are used as maximum size constraints + * on read() or write() from TUN/TAP device or TCP/UDP port. + */ +#define MAX_RW_SIZE_TUN(f) (PAYLOAD_SIZE(f)) +#define MAX_RW_SIZE_LINK(f) (EXPANDED_SIZE(f) + (f)->extra_link) + +/* + * Control buffer headroom allocations to allow for efficient prepending. + */ +#define FRAME_HEADROOM_BASE(f) (TUN_LINK_DELTA(f) + (f)->extra_buffer + (f)->extra_link) +#define FRAME_HEADROOM(f) frame_headroom(f, 0) +#define FRAME_HEADROOM_ADJ(f, fm) frame_headroom(f, fm) + +/* + * Max size of a buffer used to build a packet for output to + * the TCP/UDP port. + */ +#define BUF_SIZE(f) (TUN_MTU_SIZE(f) + FRAME_HEADROOM_BASE(f) * 2) + +/* + * Function prototypes. + */ + +void frame_finalize (struct frame *frame, + bool link_mtu_defined, + int link_mtu, + bool tun_mtu_defined, + int tun_mtu); + +void frame_subtract_extra (struct frame *frame, const struct frame *src); + +void frame_print (const struct frame *frame, + int level, + const char *prefix); + +void set_mtu_discover_type (int sd, int mtu_type); +int translate_mtu_discover_type_name (const char *name); + +/* + * frame_set_mtu_dynamic and flags + */ + +#define SET_MTU_TUN (1<<0) /* use tun/tap rather than link sizing */ +#define SET_MTU_UPPER_BOUND (1<<1) /* only decrease dynamic MTU */ + +void frame_set_mtu_dynamic (struct frame *frame, int mtu, unsigned int flags); + +/* + * allocate a buffer for socket or tun layer + */ +void alloc_buf_sock_tun (struct buffer *buf, + const struct frame *frame, + const bool tuntap_buffer, + const unsigned int align_mask); + +/* + * EXTENDED_SOCKET_ERROR_CAPABILITY functions -- print extra error info + * on socket errors, such as PMTU size. As of 2003.05.11, only works + * on Linux 2.4+. + */ + +#if EXTENDED_SOCKET_ERROR_CAPABILITY + +void set_sock_extended_error_passing (int sd); +const char *format_extended_socket_error (int fd, int *mtu, struct gc_arena *gc); + +#endif + +/* + * Calculate a starting offset into a buffer object, dealing with + * headroom and alignment issues. + */ +static inline int +frame_headroom (const struct frame *f, const unsigned int flag_mask) +{ + const int offset = FRAME_HEADROOM_BASE (f); + const int adjust = (flag_mask & f->align_flags) ? f->align_adjust : 0; + const int delta = ((PAYLOAD_ALIGN << 24) - (offset + adjust)) & (PAYLOAD_ALIGN - 1); + return offset + delta; +} + +/* + * frame member adjustment functions + */ + +static inline void +frame_add_to_extra_frame (struct frame *frame, const int increment) +{ + frame->extra_frame += increment; +} + +static inline void +frame_add_to_extra_tun (struct frame *frame, const int increment) +{ + frame->extra_tun += increment; +} + +static inline void +frame_add_to_extra_link (struct frame *frame, const int increment) +{ + frame->extra_link += increment; +} + +static inline void +frame_add_to_extra_buffer (struct frame *frame, const int increment) +{ + frame->extra_buffer += increment; +} + +static inline void +frame_add_to_align_adjust (struct frame *frame, const int increment) +{ + frame->align_adjust += increment; +} + +static inline void +frame_align_to_extra_frame (struct frame *frame) +{ + frame->align_adjust = frame->extra_frame + frame->extra_link; +} + +static inline void +frame_or_align_flags (struct frame *frame, const unsigned int flag_mask) +{ + frame->align_flags |= flag_mask; +} + +static inline bool +frame_defined (const struct frame *frame) +{ + return frame->link_mtu > 0; +} + +#endif |