[sr-dev] git:master: Small formatting updates

Module: sip-router Branch: master Commit: e783a10daaa976960065b3750bdfd727676f9310 URL: http://git.sip-router.org/cgi-bin/gitweb.cgi/sip-router/?a=commit;h=e783a10… Author: oej <oej(a)edvina.net> Committer: oej <oej(a)edvina.net> Date: Fri Oct 9 22:33:11 2009 +0200 Small formatting updates --- doc/dns.txt | 82 +++++++++++++++++++++++++++++++--------------------------- 1 files changed, 44 insertions(+), 38 deletions(-) diff --git a/doc/dns.txt b/doc/dns.txt index 1a3d904..cf595eb 100644 --- a/doc/dns.txt +++ b/doc/dns.txt @@ -7,83 +7,86 @@ # Overview +-------- - The dns subsystem in ser can either directly use libresolv and a combination + The dns subsystem in sip-router can either directly use libresolv and a combination of the locally configured dns server, /etc/hosts and the local Network Information Service (NIS/YP a.s.o) or cache the query results (both positive and negative) and look first in its internal cache. - When its internal dns cache is enabled, ser can also use dns failover: if - one destination resolves to multiple addresses ser can try all of them until + When its internal dns cache is enabled, sip-router can also use dns failover: if + one destination resolves to multiple addresses sip-router can try all of them until it finds one to which it can successfully send the packet or it exhausts all - of them. ser (tm to be more precise) uses the dns failover also when the - destination host doesn't send any reply to a forwarded invite within the - sip timeout interval (whose value can be configured using the tm fr_timer - parameter). - When SRV based load balancing is enabled ser can even do DNS based load - balancing (see RFC2782 and the dns_srv_lb option below). + of them. sip-router (The tm module to be more precise) uses the DNS failover also + when the destination host doesn't send any reply to a forwarded invite within the + SIP timeout interval (whose value can be configured using the tm fr_timer + parameter). + When SRV based load balancing is enabled sip-router can even do DNS based load + balancing (see RFC2782 and the dns_srv_lb option below). DNS Cache and Failover Drawbacks +-------------------------------- - Using the dns cache and the dns failover has also some drawbacks: + Using the DNS cache and the DNS failover has also some drawbacks: - 1. only the locally configured dns server (usually in /etc/resolv.conf) is + 1. only the locally configured DNS server (usually in /etc/resolv.conf) is used for the requests (/etc/hosts and the local Network Information Service are ignored). - Workaround: disable the dns cache (use_dns_cache=off or - compile without -DUSE_DNS_CACHE). + Workaround: disable the dns cache (use_dns_cache=off or compile without -DUSE_DNS_CACHE). - 2. the dns cache uses extra memory - Workaround: disable the dns cache. + 2. the DNS cache uses extra memory + Workaround: disable the DNS cache. - 3. the dns failover introduces a very small performance penalty - Workaround: disable the dns failover (use_dns_failover=off). + 3. the DNS failover introduces a very small performance penalty + Workaround: disable the DNS failover (use_dns_failover=off). - 4. the dns failover increases the memory usage (the internal structures - used to represent the transaction are bigger when the dns failover support is - compiled). - Workaround: compile without dns failover support (-DUSE_DNS_FAILOVER). - Turning it off from the config file is not enough in this case (the extra - memory will still be used). + 4. the DNS failover increases the memory usage (the internal structures + used to represent the transaction are bigger when the DNS failover support is + compiled). + Workaround: compile without DNS failover support (-DUSE_DNS_FAILOVER). + Turning it off from the config file is not enough in this case (the extra + memory will still be used). - On the other hand using the dns cache saves lots of DNS queries and makes + On the other hand using the DNS cache saves lots of DNS queries and makes DNS based failover and DNS based load balancing possible. If the destination - blacklist is enabled, ser can do failover even if forwarding in stateless + blacklist is enabled, sip-router can do failover even if forwarding in stateless mode. - In the ideal case with dns cache enabled ser will do only one query for + In the ideal case with the DNS cache enabled sip-router will do only one query for a NAPTR (if enabled) or SRV lookup and then it will use the results for the record's TTL (for example if all the resulting records have 1 minute TTL, - ser won't make another query for this domain for 1 minute). Even negative + the server won't make another query for this domain for 1 minute). Even negative answers will be cached. - Without the dns cache, each NAPTR or SRV lookup will result in at least 2 + Without the DNS cache, each NAPTR or SRV lookup will result in at least 2 queries. These queries will happen every time, for each message (even if all of them go to the same domain). DNS Resolver Options +-------------------- - The DNS resolver options control how ser will interact with the external + The DNS resolver options control how sip-router will interact with the external DNS servers. These options (with the dns_try_ipv6 exception) are passed to libresolv and are used each time a dns request is made. + The default values are system specific and generally depend on the /etc/resolv.conf content. For servers doing a lot of DNS requests it is - highly recommended to change the default values in the ser config file - (even if using ser's internal dns cache). + highly recommended to change the default values in the sip-router config file + (even if using sip-router's internal dns cache). - dns_try_ipv6 = on | off - if on and ser listens on at least one ipv6 socket, + dns_try_ipv6 = on | off - if on and sip-router listens on at least one ipv6 socket, ipv6 (AAAA) lookups will be performed if the ipv4 (A) lookups fail. If off only ipv4 (A) lookups will be used. - Default: on if ser is compiled with ipv6 support. + Default: on if sip-router is compiled with ipv6 support. - dns_try_naptr = on | off - if on ser will first try a NAPTR lookup for + dns_try_naptr = on | off - if on sip-router will first try a NAPTR lookup for destinations that don't have the protocol or port specified and are not simple ip addresses (as described in RFC 3263). This will introduce a slight performance penalty and will probably cause extra DNS lookups. For example a lookup for a non-existing domain will produce one extra query: NAPTR(domain), SRV(_sip._udp.domain) and A/AAAA(domain). - If the result of a query contains several NAPTR records, ser will select - among them according to the RFC2915 and ser preference towards a + If the result of a query contains several NAPTR records, sip-router will select + among them according to the RFC2915 and sip-router preference towards a specific protocol (see dns_udp_pref, dns_tcp_pref and dns_tls_pref below). For an RFC3263 compliant configuration (choose the remote side preferred protocol if supported), set dns_udp_pref, dns_tcp_pref and @@ -166,6 +169,7 @@ DNS Resolver Options DNS Resolver Compile Options +---------------------------- USE_NAPTR - if defined the naptr lookup support will be compiled in. NAPTR support still has to be enabled from ser's config file (it's @@ -179,6 +183,7 @@ DNS Resolver Compile Options DNS Cache and Failover Config Variables +--------------------------------------- use_dns_cache = on | off - if off the dns cache won't be used (all dns lookups will result into a dns request). When on all the dns request @@ -270,6 +275,7 @@ DNS Cache and Failover Config Variables Default: on DNS Cache Compile Options +------------------------- USE_DNS_CACHE - if defined the dns cache support will be compiled in (default). If not needed/wanted the dns_cache can be disabled from the @@ -309,8 +315,8 @@ DNS Cache Compile Options DNS_CACHE_DEBUG - if defined the dns cache will be very verbose (it will log lots of messages at the L_DBG levell). - Note: To remove a compile options, edit ser's Makefile.defs and remove it - form DEFS list. To add a compile options add it to the make command line, + Note: To remove a compile options, edit sip-router's Makefile.defs and remove it + from DEFS list. To add a compile options add it to the make command line, e.g.: make proper; make all extra_defs=-DUSE_DNS_FAILOVER or for a permanent solution, edit Makefile.defs and add it to DEFS (don't foget to prefix it with -D). Some options require editing