Install/data/WiFi1.cab/dualserver.zip/Replication.ReadMe.txt Driver File Contents (WiFi_Intel_Win8_64_VER16608.zip)

Driver Package File Name: WiFi_Intel_Win8_64_VER16608.zip
File Size: 118.0 MB

This version of Dual Server support replication.

FEATURES

1.	It supports Full Zone Transfer AXFR only, it does not support IXFR (incremental Zone Transfer)
2.	When Dual Server starts, it pulls RRs from other Server (see below).
3.	It do not send Notify message.
4.	It supports DHCP Database replication using special DHCP INFORM message.
5.	One Dual Server can be in Linux while other can be on Windows, it works same way.

REPLICATION SCHEMES

	DNS Server loads STATIC-HOST, MX and ALIAS records and serves them. If DHCP Service is also
	enabled, thoes records are also served by DNS Server.

	How about this server going down. A secondary server is also put in service, which just backs
	up data from Primary Server and serves it if primary server is down. Secondary server should
	have exact same data and hence it pulls the whole data (all records of a Zone) from Primary
	Server and also needs to refresh its data from Primary Server, as data on Primary Server may
	change.

	Dual Server can be used as Primary Server and also Secondary Server or a Third Party Server
	can also be used as Primary or Secondary Server with Dual Server. Dual Server supports following
	arrangements:-

1. Dual Server with only DNS Service as Primary and Secondary Server.

	This is the simple most arragement. When primary server is started it reads ALIASes, MX and
	STATIC-HOST records from it's ini file. When Secondary Server starts, it does not read these
	entries from its' ini file, but pulls the full zone from Primary Server. Secondary Server keeps
	checking the Serial from Primary Server, using UDP SOA query, if Serial advances, full zone
	is transfered from Primary.

	If any changes are made in ini file of Primay Server, it needs to be restarted and thereafter
	Secondary Server would pull automatically all RRs from Primary, after refresh time.
	
	Dual Servers do not support NOTIFY.

2. Dual Server with DNS and DHCP as Primary Server and Dual Server with only DNS as Secondary Server

	This is the conventional arrangement.

	When Primary Server starts, it reads Hosts, MX, CNAMEs from ini file. When Secondary
	server starts/restarts, it pulls Static-Host, MX, Alises and DHCP added RRs from Primary Server.
	Secondary Server keeps updating its database through convensional refresh after refresh time.

	When any DHCP lease is added or renewed or released at Primary Server, its serial number
	advances and secondary DNS Server gets this entry when refresh takes place. Secondary
	server keeps checking the serial of primary and if it advances, full zone is refreshed at
	secondary server. Similarly changing the Static Entries at Primary Server (followed by
	restart) also advances its serial and Secondary refreshes automatically.
	
3.  Dual Server with DNS and DHCP as Primary Server and third party DNS server as Secondary Server.

	This arragement too works similar to 2. Dual Server supports only full zone tranfer.
	Dual Server do not send NOTIFY message and do not send increment zone trasfer.
	The secondary server needs to pull the full zone after refresh time.
	
	The advantage is that all DHCP alloted RRs are also transfered with zone transfer to secondary
	server.

4.  Dual Server as secondary server and third party server as primary server.

	This arragement too works similar to 2. However third party primary DNS Server might update its
	database through DHCP Dynamic update or some other mechanism. Secondary Dual Server would get
	updated full zone after refresh time.

5. Dual Server with only DHCP Service as Primary and Secondary Server.

	This arragement provide backup DHCP Server. As both the DHCP Servers are in operation, new 
	lease may be alloted by any server on a Client Request. However special DHCP INFORM message
	keep the database of both servers in synch.

	When any DHCP lease is added or renewed or released by Primary Server or Secondary Server,
	the DHCP Entry is automatically duplicated in other server.
	
	Under this arragement, if any DHCP server goes down, other is available and will not allot
	already allotted IPs.

6. Dual Server with DNS and DHCP as Primary Server and Dual Server with DNS and DHCP as Secondary Server

	This is the recommended arragement.

	When Primary Server starts, it reads MX, Hosts and CNAMEs from ini file. it also pulls DHCP
	added RRs from secondary server, if secondary server is running. When Secondary server starts,
	it pulls Static-Host, MX, Alises and DHCP added RRs from Primary Server by initial zone tranfer.
	Zone transfer happens only once, when Seconadary Servers starts/restarts.

	When any DHCP lease is added or renewed or released at Primary Server or Secondary Server,
	the DHCP Entry and RR along with Serial is duplicated in other server, through unicast
	DHCP inform messases. Serial also advances on both Servers.

	This is on the assumption that only changes takes place in Zone RRs, are by DHCP server.
	Thus both servers always remains in synch.

	If any changes are manually made to ALIASs, STATIC-HOSTS or MX enties in Primary Server,
	Primary Server needs to be manually restarted and thereafter secondary server needs to be
	manually restarted. Thus these changes gets duplicated in Secondary Server.

	This arrangement provides fully synchronized fail safe duplicate DNS and DHCP Server, with
	instant replication.
	
	Under this arrangement, Secondary Server does not do peridical refresh, but rely on DHCP
	inform messages.
		
7.	Dual Server with only DNS (or third party DNS) as Primary and Dual Server with DHCP as Seocondary.

	This arrangement is not recommeded, as Primary will not be updated of changes to Secondary
	due to DHCP changes.
	
	
Future Releases of Dual Server may support NOTIFY and Increment Zone Transfers.
	
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