Transcript Lecture 31

Telecommunications Networking
II
Lecture 31
Internet(working) Protocol (IP)
(Continued)
Tanenbaum pp 431-437
Copyright 1999, S.D. Personick. All Rights Reserved.
IP- Multicasting
• Uses a special “Class D” IP address:
1110XXXX + 3 bytes (224.0.0.0 239.255.255.255)
• There are some permanent group addresses:
e.g., 224.0.0.1 => all hosts on a LAN
• Temporary group addresses are created to
form ad-hoc groups
Copyright 1999, S.D. Personick. All Rights Reserved.
IP- Multicasting
• A protocol called the Internet Group
Management Protocol (IGMP) is used by
special routers, called multicast routers, to
determine which hosts on the LANs
connected to those routers wish to belong to
one or more multicast groups. I.e., you elect
to join a multicast group
• Multicast routers form “spanning trees” to
distribute multicast packets
Copyright 1999, S.D. Personick. All Rights Reserved.
Spanning Tree
Copyright 1999, S.D. Personick. All Rights Reserved.
Spanning Tree
Copyright 1999, S.D. Personick. All Rights Reserved.
IP- Multicasting
• IP multicasting is used to broadcast audio
and audio-visual programs (MBONE) over
the Internet
Copyright 1999, S.D. Personick. All Rights Reserved.
Mobile IP
• How to accommodate Internet hosts that
move away from their “home location”
• Solution: Reinvent “call forwarding” (with
a twist) and cellular roaming
-Networks that support mobile IP provide
“home agents” and “foreign agents”
-Hosts that arrive at a foreign network
register with the local foreign agent
Copyright 1999, S.D. Personick. All Rights Reserved.
Mobile IP
• The local foreign agent contacts the visitor’s
home agent, and provides a “forwarding
address” (usually the IP address of the
foreign agent)
• Datagrams sent to the mobile host’s normal
IP address are picked up by the mobile
host’s home agent…and forwarded inside of
another IP datagram (tunneling) to the
forwarding address
Copyright 1999, S.D. Personick. All Rights Reserved.
Tunneling
Original IP Address
IP Datagram
Foreign Agent
IP Address
IP
Header
Copyright 1999, S.D. Personick. All Rights Reserved.
Mobile IP
• The home agent also sends a datagram to
the sender of the original packet, providing
the forwarding address…so that future
datagrams can be sent directly to the foreign
agent
• The foreign agent receives the forwarded
datagram, takes it out of its IP wrapper, and
delivers the unwrapped datagram to the
mobile host
Copyright 1999, S.D. Personick. All Rights Reserved.
Mobile IP
• Issues:
-How does the home agent know that a
forwarding request is legitimate? (solution:
cryptographic authentication)
-How to delete registrations at foreign
agents when mobile (visiting) hosts leave
without de-registering (solution: timeout)
Copyright 1999, S.D. Personick. All Rights Reserved.
Classless InterDomain Routing
CIDR
• Problem: the original scheme of assigning
IP addresses, Class A, Class B and Class C,
results in very inefficient use of the total
address space.
-Class A: 127 possible (each has 256 x 256
x 256 possible host addresses) Too few
-Class B: 64 x 256 possible (each has 256 x
256 possible host addresses) Too few
Copyright 1999, S.D. Personick. All Rights Reserved.
Classless InterDomain Routing
CIDR
• Problem (continued)
-Class C: 32 x 256 x 256 possible (each has
only 256 possible host addresses)
-Router tables (in backbone routers) need to
store and manage all network address-route
pairs (~2 million possible Class C network
addresses)
Copyright 1999, S.D. Personick. All Rights Reserved.
CIDR
• Solution
-Assign networks multiples of adjacent
Class C addresses to provide for N x 256
hosts
-Backbone routers need only store one
network address-route pair for each block
on contiguous Class C addresses assigned to
the same network (not obvious)
Copyright 1999, S.D. Personick. All Rights Reserved.