What Is Multihoming?
Multihoming is a technique to improve the reliability of Internet connections, an IP network. To this end, the connection is to the Internet via at least two ISPs (Internet Service Provider, in short) ISP. With one of the ISP, the router will automatically switch all the routes that previously ran on this to the other provider.
A multihoming is usually implemented through a BGP router (e.g., Cisco routers or Linux servers with Quagga). Because of the different AS path lengths decide this is the ISP connection for a specific connection the most suitable. By using different tuning parameters (MED, Precedence) some ISPs can be individually preferred.
Multihoming implies logically that work on the network addresses with PI (Provider Independent) (see below). Under this condition, other traffic shaping mechanisms may be used to run, for example, all incoming packets through an ISP and the outgoing of a second. Another variant is the individual Internet services such as Web, FTP, database, etc. distributed between the two internet lines.
Provider Independent Address Space
Provider Independent Address Space (PI address space) are Internet Protocol addresses that are assigned by Regional Internet Registry (RIR) organizations directly to an end user organization, without still dependent on an ISP for address assignment to be.
This provides the organization the ability to switch service providers without having to change the assigned IP addresses must, or even multiple service providers simultaneously in a multihoming-use configuration.
On the other hand, this increases the granularity of the address space, as organizational networks had not yet merged with Internet service providers in large address spaces (Provider Allocated Address Space or PA address space) are.
This causes problems with routing of each address space, as described in Classless Inter-Domain Routing (CIDR), not because it can be ensured that a small CI is routed address space in all parts of the Internet.
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