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Unformatted text preview: this chapter that one way to initialize a routing table is with static
routes specified in configuration files. This is often used to set a default entry. A newer way
is to use the ICMP router advertisement and solicitation messages.
The general concept is that after bootstrapping, a host broadcasts or multicasts a router
solicitation message. One or more routers respond with a router advertisement message.
Additionally, the routers periodically broadcast or multicast their router advertisements,
allowing any hosts that are listening to update their routing table accordingly.
RFC 1256 [Deering 1991] specifies the format of these two ICMP messages. Figure 9.6
shows the format of the ICMP router solicitation message. Figure 9.7 shows the format of
the ICMP router advertisement message sent by routers. file:///D|/Documents%20and%20Settings/bigini/Docu.../homenet2run/tcpip/tcp-ip-illustrated/ip_rout.htm (14 of 17) [12/09/2001 14.46.51] Chapter 9. IP Routing Figure 9.6 Format of ICMP router solicitation message. Figure 9.7 Format of ICMP router advertisement message.
Multiple addresses can be advertised by a router in a single message. Number of addresses
is the number. Address entry size is the number of 32-bit words for each router address, and
is always 2. Lifetime is the number of seconds that the advertised addresses can be
One or more pairs of an IP address and a preference then follow. The IP address must be
one of the sending router's IP addresses. The preference level is a signed 32-bit integer
indicating the preference of this address as a default router address, relative to other router
addresses on the same subnet. Larger values imply more preferable addresses. The
preference level 0x80000000 means the corresponding address, although advertised, is
not to be used by the receiver as a default router address. The default value of the
preference is normally 0.
Router Operation file:///D|/Documents%20and%20Settings/bigini/Docu.../homenet2run/tcpip/tcp-ip-illustrated/ip_rout.htm (15 of 17) [12/09/2001 14.46.51] Chapter 9. IP Routing When a router...
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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