[ViewVC] Diff of: cvs/gvpe/doc/gvpe.protocol.7.pod

Comparing gvpe/doc/gvpe.protocol.7.pod (file contents):
Revision 1.5 by pcg, Thu Apr 21 21:13:59 2005 UTC vs.
Revision 1.6 by pcg, Sun Aug 10 23:04:05 2008 UTC

 The first part of this document describes the transport protocols which
 are used by GVPE to send it's data packets over the network.
 =head1 PART 1: Transport protocols
-GVPE offers a range of transport protocols that can be used to interchange
+GVPE offers a wide range of transport protocols that can be used to
-data between nodes. Protocols differ in their overhead, speed,
+interchange data between nodes. Protocols differ in their overhead, speed,
 reliability, and robustness.
 The following sections describe each transport protocol in more
 detail. They are sorted by overhead/efficiency, the most efficient
 transport is listed first:
 between nodes.
 =head2 ICMP
 This protocol offers very low overhead (minimum 42 bytes), and can
-sometimes tunnel through firewalls when other protocols cannot.
+sometimes tunnel through firewalls when other protocols can not.
-It works by prepending a ICMP header with type C<icmp-type> and a code
+It works by prepending an ICMP header with type C<icmp-type> and a code
 of C<255>. The default C<icmp-type> is C<echo-reply>, so the resulting
 packets look like echo replies, which looks rather strange to network
 admins.
 This transport should only be used if other transports (i.e. raw ip) are
 most proxies do not allow connections to other ports.
 It is an abuse of the usage a proxy was designed for, so make sure you are
 allowed to use it for GVPE.
-This protocol also has server and client sides. If the C<tcp-port> is set
+This protocol also has server and client sides. If the C<tcp-port> is
-to zero, other nodes cannot connect to this node directly (and C<tcp-port>
+set to zero, other nodes cannot connect to this node directly. If the
-zero cannot be used). If the C<tcp-port> is non-zero, the node can act
+C<tcp-port> is non-zero, the node can act both as a client as well as a
-both as a client as well as a server.
+server.
 =head2 DNS
 B<WARNING:> Parsing and generating DNS packets is rather tricky. The code
 almost certainly contains buffer overflows and other, likely exploitable,
 traffic even if it doesn't need to transport packets.
 In addition, the same problems as the TCP transport also plague this
 protocol.
-Most configuration needs to be done by editing C<src/vpn_dns.C> directly.
 It's only use is to tunnel through firewalls that do not allow direct
 internet access. Similar to using a HTTP proxy (as the TCP transport
 does), it uses a local DNS server/forwarder (given by the C<dns-forw-host>
 configuration value) as a proxy to send and receive data as a client,
-and a C<NS> record pointing to the GVPE server (as given by the
+and an C<NS> record pointing to the GVPE server (as given by the
 C<dns-hostname> directive).
 The only good side of this protocol is that it can tunnel through most
-firewalls undetected, iff the local DNS server/forwarder is sane (which is
+firewalls mostly undetected, iff the local DNS server/forwarder is sane
-true for most routers, wlan gateways and nameservers).
+(which is true for most routers, WLAN gateways and nameservers).
+Finetuning needs to be done by editing C<src/vpn_dns.C> directly.
 =head1 PART 2: The GNU VPE protocol
 This section, unfortunately, is not yet finished, although the protocol
 is stable (until bugs in the cryptography are found, which will likely
 The TYPE field is a single byte and determines the purpose of the packet
 (e.g. RESET, COMPRESSED/UNCOMPRESSED DATA, PING, AUTH REQUEST/RESPONSE,
 CONNECT REQUEST/INFO etc.).
 SRCDST is a three byte field which contains the source and destination
-node ids (12 bits each). The protocol does not yet scale well beyond 30+
+node IDs (12 bits each).
-hosts, since all hosts must connect to each other once on startup. But if
-restarts are rare or tolerable and most connections are on demand, much
-larger networks are feasible.
 The DATA portion differs between each packet type, naturally, and is the
 only part that can be encrypted. Data packets contain more fields, as
 shown:
 the data for encryption purposes.
 SEQNO is a 32-bit sequence number. It is negotiated at every connection
 initialization and starts at some random 31 bit value. VPE currently uses
 a sliding window of 512 packets/sequence numbers to detect reordering,
-duplication and reply attacks.
+duplication and replay attacks.
-=head2 The authentification protocol
+=head2 The authentication protocol
 Before hosts can exchange packets, they need to establish authenticity of
 the other side and a key. Every host has a private RSA key and the public
 RSA keys of all other hosts.
-A host establishes a simplex connection by sending the other host a
+A host establishes a simplex connection by sending the other host an
 RSA encrypted challenge containing a random challenge (consisting of
 the encryption key to use when sending packets, more random data and
 PKCS1_OAEP padding) and a random 16 byte "challenge-id" (used to detect
 duplicate auth packets). The destination host will respond by replying
 with an (unencrypted) RIPEMD160 hash of the decrypted challenge, which
-will authentify that host. The destination host will also set the outgoing
+will authenticate that host. The destination host will also set the
-encryption parameters as given in the packet.
+outgoing encryption parameters as given in the packet.
 When the source host receives a correct auth reply (by verifying the
 hash and the id, which will expire after 120 seconds), it will start to
 accept data packets from the destination host.
 =head2 Retrying
 When there is no response to an auth request, the host will send auth
 requests in bursts with an exponential backoff. After some time it will
-resort to PING packets, which are very small (8 bytes) and lightweight
+resort to PING packets, which are very small (8 bytes + protocol header)
-(no RSA operations required). A host that receives ping requests from an
+and lightweight (no RSA operations required). A host that receives ping
-unconnected peer will respond by trying to create a connection.
+requests from an unconnected peer will respond by trying to create a
+connection.
 In addition to the exponential backoff, there is a global rate-limit on
 a per-IP base. It allows long bursts but will limit total packet rate to
 something like one control packet every ten seconds, to avoid accidental
 floods due to protocol problems (like a RSA key file mismatch between two
 hosts).
+The intervals between retries are limited by the C<max-retry>
+configuration value. A node with C<connect> = C<always> will always retry,
+a node with C<connect> = C<ondemand> will only try (and re-try) to connect
+as long as there are packets in the queue, usually this limits the retry
+period to C<max-ttl> seconds.
+Sending packets over the VPN will reset the retry intervals as well, which
+means as long as somebody is trying to send packets to a given node, GVPE
+will try to connect every few seconds.
 =head2 Routing and Protocol translation
-The gvpe routing algorithm is easy: there isn't any routing. GVPE always
+The GVPE routing algorithm is easy: there isn't much routing to speak
-tries to establish direct connections, if the protocol abilities of the
+of: When routing packets to another node, GVPE trues the following
-two hosts allow it.
+options, in order:
+=over 4
-If the two hosts should be able to reach each other (common protocol, ip
+=item If the two hosts should be able to reach each other directly (common
-and port all known), but cannot (network down), then there will be no
+protocol, port known), then GVPE will send the packet directly to the
-connection, point.
+other node.
+=item If this isn't possible (e.g. because the node doesn't have a
+C<hostname> or known port), but the nodes speak a common protocol and a
+router is available, then GVPE will ask a router to "mediate" between both
+nodes (see below).
+=item If a direct connection isn't possible (no common protocols) or
+forbidden (C<deny-direct>) and there are any routers, then GVPE will try
+to send packets to the router with the highest priority that is connected
+already I<and> is able (as specified by the config file) to connect
+directly to the target node.
+=item If no such router exists, then GVPE will simply send the packet to
+the node with the highest priority available.
+=item Failing all that, the packet will be dropped.
+=back
 A host can usually declare itself unreachable directly by setting it's
 port number(s) to zero. It can declare other hosts as unreachable by using
-a config-file that disables all protocols for these other hosts.
+a config-file that disables all protocols for these other hosts. Another
+option is to disable all protocols on that host in the other config files.
 If two hosts cannot connect to each other because their IP address(es)
-are not known (such as dialup hosts), one side will send a connection
+are not known (such as dialup hosts), one side will send a I<mediated>
-request to a router (routers must be configured to act as routers!), which
+connection request to a router (routers must be configured to act as
-will send both the originating and the destination host a connection info
+routers!), which will send both the originating and the destination host
-request with protocol information and IP address of the other host (if
+a connection info request with protocol information and IP address of the
-known). Both hosts will then try to establish a connection to the other
+other host (if known). Both hosts will then try to establish a direct
-peer, which is usually possible even when both hosts are behind a NAT
+connection to the other peer, which is usually possible even when both
-gateway.
+hosts are behind a NAT gateway.
-If the hosts cannot reach each other because they have no common protocol,
+Routing via other nodes works because the SRCDST field is not encrypted,
-the originator instead use the router with highest priority and matching
-protocol as peer. Since the SRCDST field is not encrypted, the router host
-can just forward the packet to the destination host. Since each host uses
+so the router can just forward the packet to the destination host. Since
-it's own private key, the router will not be able to decrypt or encrypt
+each host uses it's own private key, the router will not be able to
-packets, it will just act as a simple router and protocol translator.
+decrypt or encrypt packets, it will just act as a simple router and
+protocol translator.
-When no router is connected, the host will aggressively try to connect to
-all routers, and if a router is asked for an unconnected host it will try
-to ask another router to establish the connection.
-... more not yet written about the details of the routing, please bug me
-...

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Comparing gvpe/doc/gvpe.protocol.7.pod (file contents): Revision 1.5 by pcg, Thu Apr 21 21:13:59 2005 UTC vs. Revision 1.6 by pcg, Sun Aug 10 23:04:05 2008 UTC

Diff Legend

Comparing gvpe/doc/gvpe.protocol.7.pod (file contents):
Revision 1.5 by pcg, Thu Apr 21 21:13:59 2005 UTC vs.
Revision 1.6 by pcg, Sun Aug 10 23:04:05 2008 UTC