Lectures notes for 2010 - KTH

Problems with the dual functions of IP
addresses
Unfortunatelly an IP address has dual functions:
• Network ID portion indicates a location in the network
• i.e., the network ID binds the address to a location in the network topology
• CIDR and hierarchical address prefixes - allow for recursive subdivision of the topology
• Host ID portion identifies an interface - often used as a node identifier
• Unfortunately network connections are bound to these identifiers
• Specifically TCP/UDP sockets are identified by the endpoint IP address (and port numbers)
• DNS returns one or more IP addresses for new connections
⇒ This is bad for mobility and multi-homing (see textbook figure 4.12 on pg. 95)
• If a host changes its point of network attachment it must change its identity
– Later we will see how Mobile IP addresses this problem
• Host with multiple interfaces are limited in how they can use them
– Later we will see how SCTP addresses part of this problem
The result has been that multiple and dynamic addresses are difficult to handle and
lead to a number of efforts to rethink how addresses are used.
Maguire Problems with the dual functions of IP addresses 1: 98 of 104
maguire@kth.se 2010.03.21 Internetworking/Internetteknik