root/include/linux/netfilter/nf_conntrack_proto_gre.h

INCLUDED FROM

#ifndef _CONNTRACK_PROTO_GRE_H
#define _CONNTRACK_PROTO_GRE_H
#include <asm/byteorder.h>

/* GRE PROTOCOL HEADER */

/* GRE Version field */
#define GRE_VERSION_1701        0x0
#define GRE_VERSION_PPTP        0x1

/* GRE Protocol field */
#define GRE_PROTOCOL_PPTP       0x880B

/* GRE Flags */
#define GRE_FLAG_C              0x80
#define GRE_FLAG_R              0x40
#define GRE_FLAG_K              0x20
#define GRE_FLAG_S              0x10
#define GRE_FLAG_A              0x80

#define GRE_IS_C(f)     ((f)&GRE_FLAG_C)
#define GRE_IS_R(f)     ((f)&GRE_FLAG_R)
#define GRE_IS_K(f)     ((f)&GRE_FLAG_K)
#define GRE_IS_S(f)     ((f)&GRE_FLAG_S)
#define GRE_IS_A(f)     ((f)&GRE_FLAG_A)

/* GRE is a mess: Four different standards */
struct gre_hdr {
#if defined(__LITTLE_ENDIAN_BITFIELD)
        __u16   rec:3,
                srr:1,
                seq:1,
                key:1,
                routing:1,
                csum:1,
                version:3,
                reserved:4,
                ack:1;
#elif defined(__BIG_ENDIAN_BITFIELD)
        __u16   csum:1,
                routing:1,
                key:1,
                seq:1,
                srr:1,
                rec:3,
                ack:1,
                reserved:4,
                version:3;
#else
#error "Adjust your <asm/byteorder.h> defines"
#endif
        __be16  protocol;
};

/* modified GRE header for PPTP */
struct gre_hdr_pptp {
        __u8   flags;           /* bitfield */
        __u8   version;         /* should be GRE_VERSION_PPTP */
        __be16 protocol;        /* should be GRE_PROTOCOL_PPTP */
        __be16 payload_len;     /* size of ppp payload, not inc. gre header */
        __be16 call_id;         /* peer's call_id for this session */
        __be32 seq;             /* sequence number.  Present if S==1 */
        __be32 ack;             /* seq number of highest packet received by */
                                /*  sender in this session */
};

struct nf_ct_gre {
        unsigned int stream_timeout;
        unsigned int timeout;
};

#ifdef __KERNEL__
#include <net/netfilter/nf_conntrack_tuple.h>

struct nf_conn;

/* structure for original <-> reply keymap */
struct nf_ct_gre_keymap {
        struct list_head list;
        struct nf_conntrack_tuple tuple;
};

/* add new tuple->key_reply pair to keymap */
int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
                         struct nf_conntrack_tuple *t);

/* delete keymap entries */
void nf_ct_gre_keymap_destroy(struct nf_conn *ct);

void nf_nat_need_gre(void);

#endif /* __KERNEL__ */
#endif /* _CONNTRACK_PROTO_GRE_H */