RouterA router is a hardware component used to interconnect networks. Routers are devices whose primary purpose is to connect two or more networks and to filter network signals so that only desired information travels between them. Routers are much more powerful than bridges
- A router has interfaces on multiple networks
- Networks can use different technologies
- A router forwards packets between networks
- Transforms packets as necessary to meet standards for each network
- Routers are distinguished by the functions they perform:
- Internal routers: Only route packets within one area.
- Area border routers: Connect to areas together
- Backbone routers: Reside only in the backbone area
- AS boundary routers: Routers that connect to a router outside the AS.
- Routers operate primarily by examining incoming data for its network routing and transport information.
- Based on complex, internal tables of network information that it compiles, a router then determines whether or not it knows how to forward the data packet towards its destination.
- Routers can be programmed to prevent information from being sent to or received from certain networks or computers based on all or part of their network routing addresses.
- Routers also determine some possible routes to the destination network and then choose the one that promises to be the fastest.
Two key router functions of Router:
- Run routing algorithms/protocol (RIP, OSPF, BGP)
- Forwarding datagrams from incoming to outgoing link.
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
Internet Control Massage Protocol (ICMP)
Internet Group Management Protocol(IGMP)
Addressing at Network Layer
- Packet-screening firewalls examine incoming and outgoing packets for their network address information. You can use packet-screening firewalls to restrict access to specific Web sites or to permit access to your network only from specific Internet sites.
- Proxy servers (also called application-level gateways) operate by examining incoming or outgoing packets not only for their source or destination addresses but also for information carried within the data area (as opposed to the address area) of each network packet. The data area contains information written by the application program that created the packet—for example, your Web browser, FTP, or TELNET program. Because the proxy server knows how to examine this application-specific portion of the packet, you can permit or restrict the behaviour of individual programs.
- The Stateful inspection proxies monitor network signals to ensure that they are part of a legitimate ongoing conversation (rather than malicious insertions)
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