Ip Unnumbered; Configuring Ip Addresses; Assigning An Ip Address To An Interface - 3Com MSR 50 Series Configuration Manual

IP Unnumbered

Configuring IP
Addresses
Assigning an IP Address
to an Interface
While allowing you to create multiple logical networks within a single Class A, B,
or C network, subnetting is transparent to the rest of the Internet. All these
networks still appear as one. As subnetting adds an additional level, subnet-id, to
the two-level hierarchy with IP addressing, IP routing now involves three steps:
delivery to the site, delivery to the subnet, and delivery to the host.
In the absence of subnetting, some special addresses such as the addresses with
the net-id of all zeros and the addresses with the host-id of all ones, are not
assignable to hosts. The same is true of subnetting. When designing your
network, you should note that subnetting is somewhat a tradeoff between
subnets and accommodated hosts. For example, a Class B network can
accommodate 65,534 (2
an all-ones host-id is the broadcast address and the other with an all-zeros host-id
is the network address) hosts before being subnetted. After you break it down
into 512 (2 9 ) subnets by using the first 9 bits of the host-id for the subnet, you
have only 7 bits for the host-id and thus have only 126 (2
subnet. The maximum number of hosts is thus 64,512 (512 × 126), 1022 less after
the network is subnetted.
Class A, B, and C networks, before being subnetted, use these default masks (also
called natural masks): 255.0.0.0, 255.255.0.0, and 255.255.255.0 respectively.
Logically, to enable IP on an interface, you must assign this interface a unique IP
address. Yet, you can borrow an IP address already configured on one of other
interfaces on your device instead. This is called IP unnumbered and the interface
borrowing the IP address is called IP unnumbered interface.
You may need to use IP unnumbered to save IP addresses either when available IP
addresses are inadequate or when an interface is brought up but for occasional
use.
Besides directly assigning an IP address to an interface, you may configure the
interface to obtain one through BOOTP, DHCP, or PPP address negotiation as
alternatives. If you change the way an interface obtains an IP address, from
manual assignment to BOOTP for example, the IP address obtained from BOOTP
will overwrite the old one manually assigned.
n
Support for IP address acquisition modes varies by device.
■
This chapter only covers how to assign an IP address manually. For other
■
approaches, refer to
Configuration" on page
You may assign an interface multiple IP addresses, one primary and multiple
secondaries, to connect multiple logical subnets on the same physical subnet.
Follow these steps to assign an IP address to an interface:
To do...
Enter system view
16
- 2. Of the two deducted Class B addresses, one with
"DHCP Address Allocation" on page 566
363.
Use the command...
system-view

Configuring IP Addresses

7 - 2) hosts in each
and "PPP and MP
Remarks
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625