3com 4210 PWR 9-Port 3CR17341-91-ME 用户手册
产品代码
3CR17341-91-ME
88
C
HAPTER
7: IP A
DDRESSING
C
ONFIGURATION
Special Case IP
Addresses
The following IP addresses are for special use, and they cannot be used as host IP
addresses:
addresses:
■
IP address with an all-zeros net ID: Identifies a host on the local network. For
example, IP address 0.0.0.16 indicates the host with a host ID of 16 on the
local network.
example, IP address 0.0.0.16 indicates the host with a host ID of 16 on the
local network.
■
IP address with an all-zeros host ID: Identifies a network.
■
IP address with an all-ones host ID: Identifies a directed broadcast address. For
example, a packet with the destination address of 192.168.1.255 will be
broadcasted to all the hosts on the network 192.168.1.0.
example, a packet with the destination address of 192.168.1.255 will be
broadcasted to all the hosts on the network 192.168.1.0.
Subnetting and Masking
Subnetting was developed to address the risk of IP address exhaustion resulting
from fast expansion of the Internet. The idea is to break a network down into
smaller networks called subnets by using some bits of the host ID to create a
subnet ID. To identify the boundary between the host ID and the combination of
net ID and subnet ID, masking is used.
from fast expansion of the Internet. The idea is to break a network down into
smaller networks called subnets by using some bits of the host ID to create a
subnet ID. To identify the boundary between the host ID and the combination of
net ID and subnet ID, masking is used.
Each subnet mask comprises 32 bits related to the corresponding bits in an IP
address. In a subnet mask, the section containing consecutive ones identifies the
combination of net ID and subnet ID whereas the section containing consecutive
zeros identifies the host ID.
address. In a subnet mask, the section containing consecutive ones identifies the
combination of net ID and subnet ID whereas the section containing consecutive
zeros identifies the host ID.
Figure 35 shows how a Class B network is subnetted.
Figure 35 Subnet a Class B network
Table 48 IP address classes and ranges
Class
Address range
Description
A
0.0.0.0 to 127.255.255.255
Address 0.0.0.0 means this host no
this network. This address is used by
a host at bootstrap when it does not
know its IP address. This address is
never a valid destination address.
this network. This address is used by
a host at bootstrap when it does not
know its IP address. This address is
never a valid destination address.
Addresses starting with 127 are
reserved for loopback test. Packets
destined to these addresses are
processed locally as input packets
rather than sent to the link.
reserved for loopback test. Packets
destined to these addresses are
processed locally as input packets
rather than sent to the link.
B
128.0.0.0 to 191.255.255.255
--
C
192.0.0.0 to 223.255.255.255
--
D
224.0.0.0 to 239.255.255.255
Multicast address.
E
240.0.0.0 to 255.255.255.255
Reserved for future use except for
the broadcast address
255.255.255.255.
the broadcast address
255.255.255.255.
1
Net-id
Host-id
0
Class B address
0
7
15
23
31
Mask
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Net-id
Host-id
Subnetting
Mask
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0
Subnet-id