Routers can forward packets through an internet work by maintaining routing information in a database called a routing table. The routing table typically contains the address of all known networks and routing information about that network such as:
* Interface
* Routing Path
* Next Hop
* Route Metric (Cost)
* Route Timeout
Routers build and maintain their routing database by periodically sharing information with other routers. The exact format of these exchanges is based on the routing protocol. The routing protocol determines:
* The information contained in the routing table
* How messages are routed from one network to another
* How topology changes (i.e. updates to the routing table) are communicated between routers
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Changes in routing information take some time to be propagated to all routers on the network. The term convergence is used to describe the condition when all routers have the same (or correct) routing information.
The following points illustrates about how a packet is addressed as it travels through an internet work.
* On an Ethernet network, the Data Link layer address is the MAC address. On an IP network, the IP address is the Network layer address.
* Both Data Link physical addresses and Network logical addresses are used.
* The Network address contains both a logical network address and a logical device address. IP (Network) addresses are contained in the IP header; MAC (Data Link) addresses are contained in the Ethernet frame header.
* Both the source and destination Network and Data Link addresses are typically contained in the packet.
* The Data Link destination address indicates the physical address of the next hop on the route.
* Data Link addresses in the packet change as the packet is delivered from hop to hop.
* The Network destination addresses indicate the address of the final destination device.
* Network addresses remain constant as the packet is delivered from hop to hop.
* A router uses the logical network address specified at the Network layer to forward messages to the appropriate LAN segment.
Exchange 2007 Features
High Availability