Bridgehead
From Wikipedia, the free encyclopedia
A bridgehead (also 'Bridge-head') is literally a military fortification that protects the end of a bridge that is closest to the enemy. The term has been generalized in news coverage and the vernacular to also mean any kind of defended area that is extended into hostile territory (also called a foothold or incorrectly, a beachhead), in particular the area on the farside of a 'defended river bank' or a segment of a lake or riverine coastline, such as the Bridge at Remagen, and is especially applied when such a terratory is initially seized by an amphibious assault with the tactical and strategic intent of establishing a supply line across the geographic barrier feature.
Bridgeheads typically exist for only a few days, the invading forces either being thrown back or expanding the bridgehead to create a secure defensive lodgement area before breaking out into open country as happened when the U.S. 9th Armored Division seized the Ludendorff Bridge at Remagen in 1945 during World War II. In some cases, such as during the Gallipoli Campaign in World War I, a bridgehead may exist for months.
The term has also come to be used in a figurative sense, for instance in business, where a marketing "bridgehead" might be a specialized use of a new product in a particular market segment, in preparation for selling it against entrenched competitors across an entire market.
Windows 2000 Bridgehead server
In Windows 2000 Server, bridgehead servers are the contact point for the exchange of directory information between sites. A bridgehead server is a domain controller that has been either administratively assigned or automatically chosen to replicate changes collected from other domain controllers in the site to bridgehead servers in other sites.
By default, the Active Directory replication topology generator, the Knowledge Consistency Checker (KCC), automatically chooses servers to act as bridgehead servers. However, if you are an administrator, you may select one or more domain controllers in the site to be preferred bridgehead servers. These servers are used exclusively to replicate changes collected from the site. Even though you may have administratively configured several domain controllers as preferred bridgehead servers, the KCC chooses one of these servers to become the bridgehead server for the site. However, if you choose only one bridgehead server for a particular site, and that server becomes unavailable, the KCC does not choose another domain controller to be the bridgehead server. Therefore, if you assign a preferred bridgehead server, you should assign more than one.
Multiple bridgehead servers may be required to replicate full copies of data from one site to another. This behavior depends on the transports available, the directory partitions that have to be replicated, and the availability of global catalog servers. You must assign one bridgehead server for each writable directory partition in your forest. When you assign a bridgehead server, you can establish a preferred bridgehead server for one or more protocols such as IP or SMTP. When you configure a domain controller to be the preferred bridgehead server, you must specify the transports that are preferred for replication. http://support.microsoft.com/kb/271997
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