bind/doc/design/zone

			Zones

	$Id: zone,v 1.3 1999/03/03 12:20:05 marka Exp $

Overview
	 
	Zones are the unit of delegation in the DNS and may go from holding
	RR's only at the zone top to holding the complete hierachy (private
	roots zones).  Zones are a container for the RRsets that make up the
	zone.

	Zone have certain properties associated with them.

	* name
	* class
	* master / slave / stub / hint / cache / forward
	* serial number
	* signed / unsigned
	* update periods (refresh / retry) (slave / stub)
	* last update time (slave / stub)
	* access restrictions
	* transfer restrictions (master / slave)
	* update restictions (master / slave)
	* expire period (slave / stub)
	* children => bottom
	* glue
	* rrsets / data
	* transfer "in" in progress
	* transfers "out" in progress
	* "current" check in progress
	* our masters
	* primary master name (required to auto generate our masters)
	* master file name
	* database name
	* transaction logs
	* notification lists
		* NS's
		* static additional sites (stealth servers)
		* dynamically leared sites (soa queries)


	Zones have two types of versions associated with them.

	Type 1.
		The image of the "current" zone when a AXFR out is in progress.
		There may be several of these at once but they cease to need
		to exist once the AXFR's on this version has completed.

	Type 2.
		These are virtual versions of the zone and are required to
		support IXFR requests.  While the entire contents of the old
		version does not need to be kept, a change log needs to be
		kept.  An index into this log would be useful in speeding
		up replies. These versions have an explict expiry date.

		"How long are we going to keep them operationally?"
                While there are expriry dates based on last update /
                change time + expire.  In practice holding the deltas
                for a few refresh periods should be enough.  If the network
                and servers are up one is enough.

		"How are we going to generate them from a master file?"
                UPDATE should not be the only answer to this question.
                We need a tool that takes the current zone & new zone.
                Verifies the new zone, generates a delta and feeds this
                at named.  It could well be part of ndc but does not have
                to be.


	Zones need to have certain operations performed on them. The need to
	be:

	* loaded
	* unloaded
	* dumped
	* updated (UPDATE / IXFR)
	* copied out in full (AXFR) or as partial deltas (IXFR)
	* read from
	* validated 
	* generate a delta between two given versions.
	* signed / resigned
	* maintaince
		validate current soa
		remove old deltas / consolidation
		purge stale rrsets (cache)
	* notification
		responding to
		generating

Types:

	typedef enum {
		dns_zone_none = 0,
		dns_zone_master,
		dns_zone_slave,
		dns_zone_stub,
		dns_zone_hint,
		dns_zone_cache,
		dns_zone_forward
	} dns_zonetypes_t;

	typedef struct dns_ixfr	dns_ixfr_t;

	struct dns_ixfr {
		unsigned int		magic;	/*IXFR*/
		isc_uint32_t		serial;
		time_t			expire;
		unsigned int		offset;
		ISC_LINK(dns_ixfr_t)	link;
	};

	struct dns_zone {
		unsigned int		magic;	/* ZONE */
		dns_name_t		name;
		dns_rdataclass_t	class;
		dns_zonetypes_t		type;
		dns_rbt_t		top;
		isc_uint32_t		version;
		isc_uint32_t		serial;
		isc_uint32_t		refresh;
		isc_uint32_t		retry;
		isc_uint32_t		serial;
		char			*masterfile;
		dns_acl_t		*access;
		dns_acl_t		*transfer;
		struct	{
			dns_acl_t	*acl;
			dns_scl_t	*scl;		/* tsig based acl */
		}			update;
		char			*database;
		ISC_LIST(dns_ixfr_t)	ixfr;
		...
	};

Operations:
Loading:

Functions:
	void
	dns_zone_init(dns_zone_t * zone, dns_rdataclass_t class,
			isc_mem_t *mxtc);

	void
	dns_zone_invalidate(dns_zone_t *zone);
	
	void
	dns_ixfr_init(dns_ixfr_t *ixfr, unsigned long serial, time_t expire);

	void
	dns_ixfr_invalidate(dns_ixfr_t *ixfr);

	dns_zone_axfrout(dns_zone_t *zone);