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Prepend source node ID information to UDP datagrams.

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This commit changes the layout of UDP datagrams to include the 6-byte ID
(i.e. node name hash) of the node that crafted the packet at the very
beginning of the datagram (i.e. before the seqno). Note that this only
applies to SPTPS.

This is implemented at the lowest layer, i.e. in
handle_incoming_vpn_data() and send_sptps_data() functions. Source ID is
added and removed there, in such a way that the upper layers are unaware
of its presence.

This is the first stepping stone towards supporting UDP relaying in
SPTPS, by providing information about the original sender in the packet
itself. Nevertheless, even without relaying this commit already provides
a few benefits such as being able to reliably determine the source node
of a packet in the presence of an unknown source IP address, without
having to painfully go through all node keys. This makes tinc's behavior
much more scalable in this regard.

This change does not break anything with regard to the protocol: It
preserves compatibility with 1.0 and even with older pre-1.1 releases
thanks to a minor protocol version change (17.4). Source ID information
won't be included in packets sent to nodes with minor version < 4.

One drawback, however, is that this change increases SPTPS datagram
overhead by 6 bytes (the size of the source ID itself).
This commit is contained in:
Etienne Dechamps 2014-09-27 18:13:33 +01:00
parent 092d620dbb
commit 8dd1c8a020
3 changed files with 47 additions and 27 deletions
Download patch file Download diff file Expand all files Collapse all files

5
src/net.h
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@ -32,8 +32,8 @@
#define MTU 1518 /* 1500 bytes payload + 14 bytes ethernet header + 4 bytes VLAN tag */
#endif
/* MAXSIZE is the maximum size of an encapsulated packet: MTU + seqno + padding + HMAC + compressor overhead */
#define MAXSIZE (MTU + 4 + CIPHER_MAX_BLOCK_SIZE + DIGEST_MAX_SIZE + MTU/64 + 20)
/* MAXSIZE is the maximum size of an encapsulated packet: MTU + seqno + srcid + padding + HMAC + compressor overhead */
#define MAXSIZE (MTU + 4 + sizeof(node_id_t) + CIPHER_MAX_BLOCK_SIZE + DIGEST_MAX_SIZE + MTU/64 + 20)
/* MAXBUFSIZE is the maximum size of a request: enough for a MAXSIZEd packet or a 8192 bits RSA key */
#define MAXBUFSIZE ((MAXSIZE > 2048 ? MAXSIZE : 2048) + 128)
@ -87,6 +87,7 @@ typedef union sockaddr_t {
typedef struct vpn_packet_t {
length_t len; /* the actual number of bytes in the `data' field */
int priority; /* priority or TOS */
node_id_t srcid; /* node ID of the original sender */
uint8_t seqno[4]; /* 32 bits sequence number (network byte order of course) */
uint8_t data[MAXSIZE];
} vpn_packet_t;