--- gvpe/doc/gvpe.protocol.7 2005/03/15 19:23:33 1.2 +++ gvpe/doc/gvpe.protocol.7 2008/08/11 16:02:16 1.9 @@ -1,4 +1,4 @@ -.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.14 +.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.32 .\" .\" Standard preamble: .\" ======================================================================== @@ -25,11 +25,11 @@ .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left -.\" double quote, and \*(R" will give a right double quote. | will give a -.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to -.\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C' -.\" expand to `' in nroff, nothing in troff, for use with C<>. -.tr \(*W-|\(bv\*(Tr +.\" double quote, and \*(R" will give a right double quote. \*(C+ will +.\" give a nicer C++. Capital omega is used to do unbreakable dashes and +.\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, +.\" nothing in troff, for use with C<>. +.tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- @@ -129,7 +129,7 @@ .\" ======================================================================== .\" .IX Title "GVPE.PROTOCOL 7" -.TH GVPE.PROTOCOL 7 "2005-03-15" "1.8" "GNU Virtual Private Ethernet" +.TH GVPE.PROTOCOL 7 "2008-08-10" "2.2" "GNU Virtual Private Ethernet" .SH "The GNU-VPE Protocols" .IX Header "The GNU-VPE Protocols" .SH "Overview" @@ -141,18 +141,94 @@ .PP The first part of this document describes the transport protocols which are used by \s-1GVPE\s0 to send it's data packets over the network. -.SH "PART 1: Tansport protocols" -.IX Header "PART 1: Tansport protocols" +.SH "PART 1: Transport protocols" +.IX Header "PART 1: Transport protocols" +\&\s-1GVPE\s0 offers a wide range of transport protocols that can be used to +interchange data between nodes. Protocols differ in their overhead, speed, +reliability, and robustness. +.PP +The following sections describe each transport protocol in more +detail. They are sorted by overhead/efficiency, the most efficient +transport is listed first: .Sh "\s-1RAW\s0 \s-1IP\s0" .IX Subsection "RAW IP" +This protocol is the best choice, performance\-wise, as the minimum +overhead per packet is only 38 bytes. +.PP +It works by sending the \s-1VPN\s0 payload using raw ip frames (using the +protocol set by \f(CW\*(C`ip\-proto\*(C'\fR). +.PP +Using raw ip frames has the drawback that many firewalls block \*(L"unknown\*(R" +protocols, so this transport only works if you have full \s-1IP\s0 connectivity +between nodes. .Sh "\s-1ICMP\s0" .IX Subsection "ICMP" +This protocol offers very low overhead (minimum 42 bytes), and can +sometimes tunnel through firewalls when other protocols can not. +.PP +It works by prepending an \s-1ICMP\s0 header with type \f(CW\*(C`icmp\-type\*(C'\fR and a code +of \f(CW255\fR. The default \f(CW\*(C`icmp\-type\*(C'\fR is \f(CW\*(C`echo\-reply\*(C'\fR, so the resulting +packets look like echo replies, which looks rather strange to network +admins. +.PP +This transport should only be used if other transports (i.e. raw ip) are +not available or undesirable (due to their overhead). .Sh "\s-1UDP\s0" .IX Subsection "UDP" +This is a good general choice for the transport protocol as \s-1UDP\s0 packets +tunnel well through most firewalls and routers, and the overhead per +packet is moderate (minimum 58 bytes). +.PP +It should be used if \s-1RAW\s0 \s-1IP\s0 is not available. .Sh "\s-1TCP\s0" .IX Subsection "TCP" +This protocol is a very bad choice, as it not only has high overhead (more +than 60 bytes), but the transport also retries on it's own, which leads +to congestion when the link has moderate packet loss (as both the \s-1TCP\s0 +transport and the tunneled traffic will retry, increasing congestion more +and more). It also has high latency and is quite inefficient. +.PP +It's only useful when tunneling through firewalls that block better +protocols. If a node doesn't have direct internet access but a \s-1HTTP\s0 proxy +that supports the \s-1CONNECT\s0 method it can be used to tunnel through a web +proxy. For this to work, the \f(CW\*(C`tcp\-port\*(C'\fR should be \f(CW443\fR (\f(CW\*(C`https\*(C'\fR), as +most proxies do not allow connections to other ports. +.PP +It is an abuse of the usage a proxy was designed for, so make sure you are +allowed to use it for \s-1GVPE\s0. +.PP +This protocol also has server and client sides. If the \f(CW\*(C`tcp\-port\*(C'\fR is +set to zero, other nodes cannot connect to this node directly. If the +\&\f(CW\*(C`tcp\-port\*(C'\fR is non\-zero, the node can act both as a client as well as a +server. .Sh "\s-1DNS\s0" .IX Subsection "DNS" +\&\fB\s-1WARNING:\s0\fR Parsing and generating \s-1DNS\s0 packets is rather tricky. The code +almost certainly contains buffer overflows and other, likely exploitable, +bugs. You have been warned. +.PP +This is the worst choice of transport protocol with respect to overhead +(overhead can be 2\-3 times higher than the transferred data), and latency +(which can be many seconds). Some \s-1DNS\s0 servers might not be prepared to +handle the traffic and drop or corrupt packets. The client also has to +constantly poll the server for data, so the client will constantly create +traffic even if it doesn't need to transport packets. +.PP +In addition, the same problems as the \s-1TCP\s0 transport also plague this +protocol. +.PP +It's only use is to tunnel through firewalls that do not allow direct +internet access. Similar to using a \s-1HTTP\s0 proxy (as the \s-1TCP\s0 transport +does), it uses a local \s-1DNS\s0 server/forwarder (given by the \f(CW\*(C`dns\-forw\-host\*(C'\fR +configuration value) as a proxy to send and receive data as a client, +and an \f(CW\*(C`NS\*(C'\fR record pointing to the \s-1GVPE\s0 server (as given by the +\&\f(CW\*(C`dns\-hostname\*(C'\fR directive). +.PP +The only good side of this protocol is that it can tunnel through most +firewalls mostly undetected, iff the local \s-1DNS\s0 server/forwarder is sane +(which is true for most routers, \s-1WLAN\s0 gateways and nameservers). +.PP +Finetuning needs to be done by editing \f(CW\*(C`src/vpn_dns.C\*(C'\fR directly. .SH "PART 2: The GNU VPE protocol" .IX Header "PART 2: The GNU VPE protocol" This section, unfortunately, is not yet finished, although the protocol @@ -166,9 +242,9 @@ transort protocols, be it \s-1RAWIP\s0 or \s-1TCP\s0. .PP .Vb 3 -\& +------+------+--------+------+ +\& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ \& | HMAC | TYPE | SRCDST | DATA | -\& +------+------+--------+------+ +\& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ .Ve .PP The \s-1HMAC\s0 field is present in all packets, even if not used (e.g. in auth @@ -180,19 +256,16 @@ \&\s-1CONNECT\s0 \s-1REQUEST/INFO\s0 etc.). .PP \&\s-1SRCDST\s0 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+ -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. +node IDs (12 bits each). .PP The \s-1DATA\s0 portion differs between each packet type, naturally, and is the only part that can be encrypted. Data packets contain more fields, as shown: .PP .Vb 3 -\& +------+------+--------+------+-------+------+ +\& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-+\-\-\-\-\-\-+ \& | HMAC | TYPE | SRCDST | RAND | SEQNO | DATA | -\& +------+------+--------+------+-------+------+ +\& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-+\-\-\-\-\-\-+ .Ve .PP \&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of @@ -201,21 +274,21 @@ \&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection initialization and starts at some random 31 bit value. \s-1VPE\s0 currently uses a sliding window of 512 packets/sequence numbers to detect reordering, -duplication and reply attacks. -.Sh "The authentification protocol" -.IX Subsection "The authentification protocol" +duplication and replay attacks. +.Sh "The authentication protocol" +.IX Subsection "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 \s-1RSA\s0 key and the public \&\s-1RSA\s0 keys of all other hosts. .PP -A host establishes a simplex connection by sending the other host a +A host establishes a simplex connection by sending the other host an \&\s-1RSA\s0 encrypted challenge containing a random challenge (consisting of the encryption key to use when sending packets, more random data and \&\s-1PKCS1_OAEP\s0 padding) and a random 16 byte \*(L"challenge\-id\*(R" (used to detect duplicate auth packets). The destination host will respond by replying with an (unencrypted) \s-1RIPEMD160\s0 hash of the decrypted challenge, which -will authentify that host. The destination host will also set the outgoing -encryption parameters as given in the packet. +will authenticate that host. The destination host will also set the +outgoing encryption parameters as given in the packet. .PP 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 @@ -234,48 +307,62 @@ .IX Subsection "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 \s-1PING\s0 packets, which are very small (8 bytes) and lightweight -(no \s-1RSA\s0 operations required). A host that receives ping requests from an -unconnected peer will respond by trying to create a connection. +resort to \s-1PING\s0 packets, which are very small (8 bytes + protocol header) +and lightweight (no \s-1RSA\s0 operations required). A host that receives ping +requests from an unconnected peer will respond by trying to create a +connection. .PP 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 \s-1RSA\s0 key file mismatch between two hosts). +.PP +The intervals between retries are limited by the \f(CW\*(C`max\-retry\*(C'\fR +configuration value. A node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`always\*(C'\fR will always retry, +a node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`ondemand\*(C'\fR will only try (and re\-try) to connect +as long as there are packets in the queue, usually this limits the retry +period to \f(CW\*(C`max\-ttl\*(C'\fR seconds. +.PP +Sending packets over the \s-1VPN\s0 will reset the retry intervals as well, which +means as long as somebody is trying to send packets to a given node, \s-1GVPE\s0 +will try to connect every few seconds. .Sh "Routing and Protocol translation" .IX Subsection "Routing and Protocol translation" -The gvpe routing algorithm is easy: there isn't any routing. \s-1GVPE\s0 always -tries to establish direct connections, if the protocol abilities of the -two hosts allow it. -.PP -If the two hosts should be able to reach each other (common protocol, ip -and port all known), but cannot (network down), then there will be no -connection, point. +The \s-1GVPE\s0 routing algorithm is easy: there isn't much routing to speak +of: When routing packets to another node, \s-1GVPE\s0 trues the following +options, in order: +.IP "If the two hosts should be able to reach each other directly (common protocol, port known), then \s-1GVPE\s0 will send the packet directly to the other node." 4 +.IX Item "If the two hosts should be able to reach each other directly (common protocol, port known), then GVPE will send the packet directly to the other node." +.PD 0 +.ie n .IP "If this isn't possible (e.g. because the node doesn't have a \*(C`hostname\*(C' or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ""mediate"" between both nodes (see below)." 4 +.el .IP "If this isn't possible (e.g. because the node doesn't have a \f(CW\*(C`hostname\*(C'\fR or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ``mediate'' between both nodes (see below)." 4 +.IX Item "If this isn't possible (e.g. because the node doesn't have a 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)." +.ie n .IP "If a direct connection isn't possible (no common protocols) or forbidden (\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand is able (as specified by the config file) to connect directly to the target node." 4 +.el .IP "If a direct connection isn't possible (no common protocols) or forbidden (\f(CW\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand\fR is able (as specified by the config file) to connect directly to the target node." 4 +.IX Item "If a direct connection isn't possible (no common protocols) or forbidden (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 and is able (as specified by the config file) to connect directly to the target node." +.IP "If no such router exists, then \s-1GVPE\s0 will simply send the packet to the node with the highest priority available." 4 +.IX Item "If no such router exists, then GVPE will simply send the packet to the node with the highest priority available." +.IP "Failing all that, the packet will be dropped." 4 +.IX Item "Failing all that, the packet will be dropped." +.PD .PP 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. .PP If two hosts cannot connect to each other because their \s-1IP\s0 address(es) -are not known (such as dialup hosts), one side will send a connection -request to a router (routers must be configured to act as routers!), which -will send both the originating and the destination host a connection info -request with protocol information and \s-1IP\s0 address of the other host (if -known). Both hosts will then try to establish a connection to the other -peer, which is usually possible even when both hosts are behind a \s-1NAT\s0 -gateway. -.PP -If the hosts cannot reach each other because they have no common protocol, -the originator instead use the router with highest priority and matching -protocol as peer. Since the \s-1SRCDST\s0 field is not encrypted, the router host -can just forward the packet to the destination host. Since each host uses -it's own private key, the router will not be able to decrypt or encrypt -packets, it will just act as a simple router and protocol translator. -.PP -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. -.PP -\&... more not yet written about the details of the routing, please bug me -\&... +are not known (such as dialup hosts), one side will send a \fImediated\fR +connection request to a router (routers must be configured to act as +routers!), which will send both the originating and the destination host +a connection info request with protocol information and \s-1IP\s0 address of the +other host (if known). Both hosts will then try to establish a direct +connection to the other peer, which is usually possible even when both +hosts are behind a \s-1NAT\s0 gateway. +.PP +Routing via other nodes works because the \s-1SRCDST\s0 field is not encrypted, +so the router can just forward the packet to the destination host. Since +each host uses it's own private key, the router will not be able to +decrypt or encrypt packets, it will just act as a simple router and +protocol translator.