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Notes about IP Responses to Negative Advice:
1. If an ICMP redirect message is received during dead gateway processing,
routes to a suspect gateway may be temporarily restored. However, dead
gateway PING processing is not interrupted, and subsequent negative advice
forces the IP routing table back to its previously adjusted state.
2. Responses from user-initiated PINGs can also indicate that a suspect gateway
is active.
3. Negative advice is not passed from the UDP or RAW IP protocol machines.
Applications using these protocols must use other mechanisms to detect and
respond to apparent network problems. However, data link layer-negative advice
is still used to manage problems with the first-hop gateway.
Multihoming Function
A multihomed host has multiple IP addresses, which we may think of as logical
interfaces. These logical interfaces may be associated with one or more physical
interfaces, and these physical interfaces may be connected to the same or different
networks.
The AS/400 TCP/IP implementation supports multihoming. This allows you to
specify either a single interface or multiple interfaces for a line description. You can
have your AS/400 appear as any one or combination of the following scenarios:
v A single host on a network over a communications line
v Multiple hosts on the same network over the same communications line
v Multiple hosts on the same network over multiple communications lines
v Multiple hosts on different networks over the same communications line
v Multiple hosts on different networks over multiple communications lines
Note: The maximum number of interfaces that can be active on a line description
at any given time is 128. This is true for all line types (for example,
token-ring, Ethernet, frame relay, and so forth).
Example: A Single Host on a Network over a Communications Line
Your AS/400 system uses one adapter for TCP/IP to attach to a LAN or WAN
network. You add one TCP/IP interface. This TCP/IP interface includes the Internet
address of your AS/400 system. With this single Internet address, your AS/400
system is part of a single TCP/IP network (Figure 56).
Figure 56. Multihoming - Single Host, Single Network, Single Line
Chapter 3. TCP/IP: Operation, Management, and Advanced Topics 79