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Unformatted text preview: m is sent directly to the destination. Otherwise the host sends the datagram to a default
router, and lets the router deliver the datagram to its destination. This simple scheme handles most
host configurations. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ip_inter.htm (5 of 19) [12/09/2001 14.46.37] Chapter 3. IP: Internet Protocol In this section and in Chapter 9 we'll look at the more general case where the IP layer can be
configured to act as a router in addition to acting as a host. Most multiuser systems today, including
almost every Unix system, can be configured to act as a router. We can then specify a single
routing algorithm that both hosts and routers can use. The fundamental difference is that a host
never forwards datagrams from one of its interfaces to another, while a router forwards datagrams.
A host that contains embedded router functionality should never forward a datagram unless it has
been specifically configured to do so. We say more about this configuration option in Section 9.4.
In our general scheme, IP can receive a datagram from TCP, UDP, ICMP, or IGMP (that is, a
locally generated datagram) to send, or one that has been received from a network interface (a
datagram to forward). The IP layer has a routing table in memory that it searches each time it
receives a datagram to send. When a datagram is received from a network interface, IP first checks
if the destination IP address is one of its own IP addresses or an IP broadcast address. If so, the
datagram is delivered to the protocol module specified by the protocol field in the IP header. If the
datagram is not destined for this IP layer, then (1) if the IP layer was configured to act as a router
the packet is forwarded (that is, handled as an outgoing datagram as described below), else (2) the
datagram is silently discarded.
Each entry in the routing table contains the following information:
q q q q Destination IP address. This can be either a complete host address or a network addr...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12