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| -rw-r--r-- | doc/design-thoughts/binding-possibilities.txt | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/doc/design-thoughts/binding-possibilities.txt b/doc/design-thoughts/binding-possibilities.txt new file mode 100644 index 0000000..3f5e432 --- /dev/null +++ b/doc/design-thoughts/binding-possibilities.txt @@ -0,0 +1,167 @@ +2013/10/10 - possibilities for setting source and destination addresses + + +When establishing a connection to a remote device, this device is designated +as a target, which designates an entity defined in the configuration. A same +target appears only once in a configuration, and multiple targets may share +the same settings if needed. + +The following types of targets are currently supported : + + - listener : all connections with this type of target come from clients ; + - server : connections to such targets are for "server" lines ; + - peer : connections to such target address "peer" lines in "peers" + sections ; + - proxy : these targets are used by "dispatch", "option transparent" + or "option http_proxy" statements. + +A connection might not be reused between two different targets, even if all +parameters seem similar. One of the reason is that some parameters are specific +to the target and are not easy or not cheap to compare (eg: bind to interface, +mss, ...). + +A number of source and destination addresses may be set for a given target. + + - listener : + - the "from" address:port is set by accept() + + - the "to" address:port is set if conn_get_to_addr() is called + + - peer : + - the "from" address:port is not set + + - the "to" address:port is static and dependent only on the peer + + - server : + - the "from" address may be set alone when "source" is used with + a forced IP address, or when "usesrc clientip" is used. + + - the "from" port may be set only combined with the address when + "source" is used with IP:port, IP:port-range or "usesrc client" is + used. Note that in this case, both the address and the port may be + 0, meaning that the kernel will pick the address or port and that + the final value might not match the one explicitly set (eg: + important for logging). + + - the "from" address may be forced from a header which implies it + may change between two consecutive requests on the same connection. + + - the "to" address and port are set together when connecting to a + regular server, or by copying the client's IP address when + "server 0.0.0.0" is used. Note that the destination port may be + an offset applied to the original destination port. + + - proxy : + - the "from" address may be set alone when "source" is used with a + forced IP address or when "usesrc clientip" is used. + + - the "from" port may be set only combined with the address when + "source" is used with IP:port or with "usesrc client". There is + no ip:port range for a proxy as of now. Same comment applies as + above when port and/or address are 0. + + - the "from" address may be forced from a header which implies it + may change between two consecutive requests on the same connection. + + - the "to" address and port are set together, either by configuration + when "dispatch" is used, or dynamically when "transparent" is used + (1:1 with client connection) or "option http_proxy" is used, where + each client request may lead to a different destination address. + + +At the moment, there are some limits in what might happen between multiple +concurrent requests to a same target. + + - peers parameter do not change, so no problem. + + - server parameters may change in this way : + - a connection may require a source bound to an IP address found in a + header, which will fall back to the "source" settings if the address + is not found in this header. This means that the source address may + switch between a dynamically forced IP address and another forced + IP and/or port range. + + - if the element is not found (eg: header), the remaining "forced" + source address might very well be empty (unset), so the connection + reuse is acceptable when switching in that direction. + + - it is not possible to switch between client and clientip or any of + these and hdr_ip() because they're exclusive. + + - using a source address/port belonging to a port range is compatible + with connection reuse because there is a single range per target, so + switching from a range to another range means we remain in the same + range. + + - destination address may currently not change since the only possible + case for dynamic destination address setting is the transparent mode, + reproducing the client's destination address. + + - proxy parameters may change in this way : + - a connection may require a source bound to an IP address found in a + header, which will fall back to the "source" settings if the address + is not found in this header. This means that the source address may + switch between a dynamically forced IP address and another forced + IP and/or port range. + + - if the element is not found (eg: header), the remaining "forced" + source address might very well be empty (unset), so the connection + reuse is acceptable when switching in that direction. + + - it is not possible to switch between client and clientip or any of + these and hdr_ip() because they're exclusive. + + - proxies do not support port ranges at the moment. + + - destination address might change in the case where "option http_proxy" + is used. + +So, for each source element (IP, port), we want to know : + - if the element was assigned by static configuration (eg: ":80") + - if the element was assigned from a connection-specific value (eg: usesrc clientip) + - if the element was assigned from a configuration-specific range (eg: 1024-65535) + - if the element was assigned from a request-specific value (eg: hdr_ip(xff)) + - if the element was not assigned at all + +For the destination, we want to know : + - if the element was assigned by static configuration (eg: ":80") + - if the element was assigned from a connection-specific value (eg: transparent) + - if the element was assigned from a request-specific value (eg: http_proxy) + +We don't need to store the information about the origin of the dynamic value +since we have the value itself. So in practice we have : + - default value, unknown (not yet checked with getsockname/getpeername) + - default value, known (check done) + - forced value (known) + - forced range (known) + +We can't do that on an ip:port basis because the port may be fixed regardless +of the address and conversely. + +So that means : + + enum { + CO_ADDR_NONE = 0, /* not set, unknown value */ + CO_ADDR_KNOWN = 1, /* not set, known value */ + CO_ADDR_FIXED = 2, /* fixed value, known */ + CO_ADDR_RANGE = 3, /* from assigned range, known */ + } conn_addr_values; + + unsigned int new_l3_src_status:2; + unsigned int new_l4_src_status:2; + unsigned int new_l3_dst_status:2; + unsigned int new_l4_dst_status:2; + + unsigned int cur_l3_src_status:2; + unsigned int cur_l4_src_status:2; + unsigned int cur_l3_dsp_status:2; + unsigned int cur_l4_dst_status:2; + + unsigned int new_family:2; + unsigned int cur_family:2; + +Note: this obsoletes CO_FL_ADDR_FROM_SET and CO_FL_ADDR_TO_SET. These flags +must be changed to individual l3+l4 checks ORed between old and new values, +or better, set to cur only which will inherit new. + +In the connection, these values may be merged in the same word as err_code. |