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same network that the AS/400 is attached to. You must also add routing entries to
allow TCP/IP clients that are attempting to reach your AS/400 system from a remote
network to function correctly.
For example, suppose that someone using a PC is using the TELNET application to
start a remote terminal session on your AS/400 system. The application on the PC
must know the route or path to reach the AS/400 system. Your AS/400 system must
also be able to determine the route back to the PC. If the PC and your AS/400
system are not on the same network, a routing entry must exist on the PC and on
AS/400.
Note: You should plan to have the routing table defined so that there is always an
entry for at least one default route (*DFTROUTE). If there is no match on
any other entry in the routing table, data is sent to the IP router specified by
the first available default route entry. The only exception to this is if you
intend to dial out over a SLIP link to an Internet Service Provider or another
remote host. See “Using SLIP with an Asynchronous Line Description” on
page 126 for details.
Before adding routing entries, familiarize yourself with the following terms:
Route destination
The network ID portion of an Internet address. The network ID portion is
composed of the first byte, the first two bytes, or the first three bytes of the
Internet address (depending on the network class). The remaining bytes
define the host ID portion of the Internet address.
If subnetting is used, route destination includes the subnet part as well. In
other words, the route destination equals the address of a TCP/IP
network to be reached.
Subnet mask
A bit mask that defines which part of an Internet address forms the network
and the subnetwork.
The technique known as subnet addressing, subnet routing,or
subnetting allows a single network ID to be used on multiple physical
networks. This technique lets you define separate routes to different sets of
Internet addresses within a specific network.
For more information about subnet masks and subnetworks, refer to
“Subnetworks and Subnet Masks” on page 6.
Next hop
The Internet address of the first system in the route between your system
and the destination network. The next hop value is always an Internet
address. Next hops need to be hosts on a directly connected TCP/IP
network defined by the TCP/IP interfaces.
Maximum Transmission Unit (MTU) size
The maximum size (in bytes) of IP datagrams sent on a route. If you specify
*IFC, the size is calculated for you based on values found in the AS/400
line description. The maximum size specified for a particular route must not
be larger than the smallest MTU supported by any router or bridge in that
route. If you specify a larger size, some datagrams may be lost.
In addition, the MTU specified for a particular route should not be larger
than the smallest MTU supported by any system used as an IP router for
that route. If you specify a larger size, performance may degrade as
systems attempt to divide the IP datagrams into smaller fragments.
Chapter 2. Configuring TCP/IP 33