TCP/IP Tutorial and Technical Overview - IBM Redbooks

Redirect (5)
If this message is received from an intermediate router, it means that the host
should send future datagrams for the network to the router whose IP address is
specified in the ICMP message. This preferred router will always be on the same
subnet as the host that sent the datagram and the router that returned the IP
datagram. The router forwards the datagram to its next hop destination. This
message will not be sent if the IP datagram contains a source route.
The ICMP header code field will have one of the following values:
0 Network redirect
1 Host redirect
2 Network redirect for this type of service
3 Host redirect for this type of service
See Figure 3-32 for more details.
0 8 16 31
router IP address
IP header - 64 bits of original data of the datagram
Figure 3-32 ICMP: Redirect
Router Advertisement (9) and Router Solicitation (10)
ICMP messages 9 and 10 are optional. They are described in RFC 1256, which
is elective. See Figure 3-33 and Figure 3-34 on page 114 for details.
0 8 16 31
number
entry length
router address 1
preference level 1
TTL
/ / / /
router address n
preference level n
Figure 3-33 ICMP: Router Advertisement
Chapter 3. Internetworking protocols 113