Transcript IP address
IP Addressing IP Addressing ● IPv4 addresses… ■ Uniquely identify an interface ■ 32 bits long ■ Consist of a network identifier and a host identifier 0 31 Network Identifier Host Identifier ● Routing outside of the destination host’s subnet is usually based on the network identifier, while the host identifier is only used within the destination’s subnet ● IPv6 uses 128-bit addresses Five Classes of IP Addresses ● IP addressing was originally based on five classes of addresses ■ A router can interpret the network and host fields by examining the first few bits of the IP address Class A 01234 0 netid 8 16 24 31 Class B 10 Class C 110 netid Class D 1110 multicast address Class E 1111 reserved for future use hostid netid hostid hostid Classful Addressing The address space is divided into five classes: A, B, C, D and E. Finding the classes in binary and dotted-decimal notation From Figure 19.2 of Data Communications and Networking by Forouzan, 4th CIDR ● Classless Inter-Domain Routing (CIDR) was introduced to remedy problems with the rigid classes of IP addresses ■ Defined in RFCs 1517-1520 ● Allows a flexible definition of the boundary between the network identifier and the host identifier ● Example ■ IP address: 10.1.9.52 ■ Subnet mask: 255.255.252.0 (22-bit network identifier) ■ Network: 10.1.8.0/22 ■ Packets with address in the range 10.1.8.0-10.1.11.255 will be routed to network 10.1.8.0/22 based on the first 22 bits A Problem With IP Addressing ● An IP address serves two different functions… ■ The name for an interface (host) and ■ The location (subnet) of the interface (host) in the network ● The IP address is the only “name” carried in an IP datagram ■ DNS can be used to map one or more symbolic names to one or more IP addresses, but a symbolic name is not carried in the datagram and has no meaning once the DNS lookup is completed ● The network identifier in the IP address is used by routers to deliver to the destination subnet ■ The IP address is associated with the location or subnet of the destination host IP Routing ● Router uses routing table to direct packets to the appropriate interface Target 2.0.0.0/24 3.0.0.0/24 4.0.0.0/24 Interface a b c 3.0.0.2 3.0.0.3 4.0.0.5 4.0.0.6 b a Dest = 3.0.0.4 Router c 3.0.0.4 Traditional Routing for a Mobile Host ● Host moving to another network is unreachable Target 2.0.0.0/24 3.0.0.0/24 4.0.0.0/24 Interface a b c 3.0.0.2 3.0.0.3 b X a Dest = 3.0.0.4 Router 3.0.0.4 c Mobile Host 4.0.0.5 4.0.0.6 3.0.0.4