Routes
and Protocols |
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A route is
the sequence of network nodes through which messages travel when
sent from a source node to a destination node.
A protocol is a set of rules for a
particular communication task. A protocol handler or protocol module
is a piece of software that implements a particular protocol.
Network
Interface Name |
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A network interface is
a communication path through which messages can be sent and received.
A hardware network interface has a hardware device associated with
it, such as an Ethernet, Fibre Channel, ATM, Token Ring, or FDDI
card. A software network interface does not include a hardware device,
(for example, the loopback interface). An
IP address is associated with an interface name. The interface name(s)
for a hardware network interface can be found by running the lanscan command and looking at the “Net-Interface
Name PPA” field.
For Ethernet cards, you can choose either Ethernet encapsulation
by specifying lan when configuring the interface, or IEEE 802.3
encapsulation by specifying snap when configuring the interface.
The interface name may include a colon (:), followed by a
number that denotes the logical interface number. The number 0 is
the first logical interface number for a card/encapsulation type
and is known as the initial interface. The interface name lan0 is
equivalent to lan0:0, lan1 is equivalent to lan1:0, and so on.
You must configure the initial interface for a card/encapsulation
type before you can configure subsequent interfaces for the same
card/encapsulation type. For example, you must configure lan0:0
(or lan0) before you configure lan0:1 and lan0:2. Once you have
configured the initial interface, you can configure the subsequent
interfaces in any order. Note that the IP addresses assigned to
a card may be on the same subnet or on different subnets. See the section “Interfaces,” in
Chapter 7 for more information about logical interfaces and interface names.
An initial interface cannot be removed from the system until
all subsequent logical interfaces are removed. You can remove subsequent
interfaces from the system with the ifconfig command, as in the following example:
ifconfig lan1:1 inet 0.0.0.0 |
The initial interface (for example, lan1) can then be removed
from the system with the ifconfig command, as in the following example:
A loopback interface does not have a hardware device associated
with it. The name of this type of interface is lo0, denoting the loopback interface. A loopback interface
is automatically created by the TCP/IP stack even if the system
is not connected to a network.
ARP
Cache |
|
Each
interface card on a system is identified by an IP address and a
station address. The ARP cache contains the
IP address of a remote interface and the station address which is
used to send packets to that IP address. If the remote system is
not on the same physical network, the station address in the ARP
cache is for an interface on a gateway.
Usually, an ARP cache entry is automatically created when
the system needs to send the first packet to a remote IP address.
ARP cache entries are usually deleted automatically when they have
not been used for a period of time.
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