понеделник, 10 март 2008 г.
Virtual Router PPVPN
Virtual router architectures do not need to disambiguate addresses, because rather than a PE router having awareness of all the PPVPNs, the PE contains multiple virtual router instances, which belong to one and only one VPN.
IP Classes
Class A Network - binary address start with 0, therefore the decimal number can be anywhere from 1 to 126. The first 8 bits (the first octet) identify the network and the remaining 24 bits indicate the host within the network. An example of a Class A IP address is 102.168.212.226, where "102" identifies the network and "168.212.226" identifies the host on that network.
Class B Network - binary addresses start with 10, therefore the decimal number can be anywhere from 128 to 191. (The number 127 is reserved for loopback and is used for internal testing on the local machine.) The first 16 bits (the first two octets) identify the network and the remaining 16 bits indicate the host within the network. An example of a Class B IP address is 168.212.226.204 where "168.212" identifies the network and "226.204" identifies the host on that network.
Class C Network - binary addresses start with 110, therefore the decimal number can be anywhere from 192 to 223. The first 24 bits (the first three octets) identify the network and the remaining 8 bits indicate the host within the network. An example of a Class C IP address is 200.168.212.226 where "200.168.212" identifies the network and "226" identifies the host on that network.
Class D Network - binary addresses start with 1110, therefore the decimal number can be anywhere from 224 to 239. Class D networks are used to support multicasting.
Class E Network - binary addresses start with 1111, therefore the decimal number can be anywhere from 240 to 255. Class E network are used for experimentation. They have never been documented or utilized in a standard way.
Subnet mask definition
Subnetting enables the network administrator to further divide the host part of the address into two or more subnets. In this case, a part of the host address is reserved to identify the particular subnet. This is easier to see if we show the IP address in binary format. The full address is:
10010110.11010111.00010001.00001001
The Class B network part is:
10010110.11010111
and the host address is
00010001.00001001
If this network is divided into 14 subnets, however, then the first 4 bits of the host address (0001) are reserved for identifying the subnet.
The subnet mask is the network address plus the bits reserved for identifying the subnetwork. (By convention, the bits for the network address are all set to 1, though it would also work if the bits were set exactly as in the network address.) In this case, therefore, the subnet mask would be 11111111.11111111.11110000.00000000. It's called a mask because it can be used to identify the subnet to which an IP address belongs by performing a bitwise on the mask and the IP address. The result is the subnetwork address:
Subnet Mask | 255.255.240.000 | 11111111.11111111.11110000.00000000 |
IP Address | 150.215.017.009 | 10010110.11010111.00010001.00001001 |
Subnet Address | 150.215.016.000 | 10010110.11010111.00010000.00000000 |
The subnet address, therefore, is 150.215.016.000.