1. CIDR – Classless InterDomain Routing
Running out of IP addresses
class C is too small; class B is too large (more than half of the class B networks have fewer than 50 hosts)
CIDR (Classless InterDomain Routing) allows to allocate IP address with a variable-sized block (contiguous network numbers to nearby networks), with no regard to the classes.
The routing becomes more complicated.

2. Supernetting (CIDR) Represent blocks with a single pair:
Restrict block sizes to powers of 2
Use a bit mask (CIDR mask) to identify block size
<base address, count> < , 1024>
base address/mask /
base address/bits of network part /22
All routers must understand CIDR addressing

3. CDR – Classless InterDomain Routing
5-59
A set of IP address assignments.

4. Internet Control Message Protocol
The control messages
destination unreachable
time exceeded: TTL zero, (wandering to too long)
parameter problem: header invalid
source quench, too much packets (choke packet)
fragmentation required: MTU too small.
for information messages:
echo request/reply
timestamp request/reply
Two programs that use the ICMP protocol:
ping and traceroute
IP invokes ICMP to report errors.

5. Internet Control Message Protocol
5-61
The principal ICMP message types.

6. ARP– The Address Resolution Protocol
ARP: Address Resolution Protocol
find out the Ethernet address for an IP address
a host broadcast to everyone asking “who owns IP address xxx.xxx.xxx.xxx”
The host with that IP address response with its Ethernet address.
RARP: Reverse Address Resolution Protocol
Find out a host’s IP address.
The host broadcast to everyone asking “My Ethernet address is xx:xx:xx:xx:xx:xx, who knows my IP address?”
The RARP server looks up the configuration file and reply with its IP address.

7. ARP– The Address Resolution Protocol
Three interconnected /24 networks: two Ethernets and an FDDI ring.

8. Dynamic Host Configuration Protocol
BOOTP (Bootstrap Protocol) is a protocol that lets a network user be automatically configured (receive an IP address) and have an operating system booted (initiated) without user involvement.
Needs manually configuration (a table to map MAC to IP address)
DHCP (Dynamic Host Configuration Protocol) is a communications protocol that lets network administrators manage centrally and automate the assignment of IP addresses in an organization's network.
It is not necessary to have one DHCP server on each network but a DHCP relay agent is needed on each LAN.

9. Dynamic Host Configuration Protocol
Operation of DHCP.

10. OSPF – The Interior Gateway Routing Protocol
Design goals of OSPF (Open Shortest Path First):
The algorithm should be published in the open literature.
It should support a variety of distance metrics.
It had to be a dynamic algorithm
It had to support routing based on type of service.
It had to do load balancing.
It supports for hierarchical systems.
Some security was required.
It is able to deal with routers connected to the Internet via a tunnel.

11. OSPF – The Interior Gateway Routing Protocol
OSPF supports three kinds of connections and networks:
Point-to-pint lines between exactly two routers.
Multiaccess networks with broadcasting (e.g., most LANs.)
Multiaccess networks without broadcasting (e.g., most packet-switched WANs).
A multiaccess network is one that can have multiple routers on it, each of which can directly communicate with all the others.
OSPF represents the actual network as a graph like this and then compute the shortest path from every router to every other router.

12. OSPF – The Interior Gateway Routing Protocol
(a) An autonomous system. (b) A graph representation of (a).

13. OSPF – The Interior Gateway Routing Protocol
OSPF allows systems to be divided into numbered areas, where an area is a network or a set of contiguous networks.
Every systems has a backbone area (area 0). All areas are connected to the backbone.
OSPF distinguishes four classes of routers:
Internal routers are wholly within one area.
Area border routers connect two or more areas.
Backbone routers are on the backbone
system boundary routers talk to routers in other system

14. The relation between ASes, backbones, and areas in OSPF.

15. The five types of OSPF messeges.
5-66
The five types of OSPF messeges.

16. BGP – The Exterior Gateway Routing Protocol
BGP (Border Gateway Protocol) is a protocol for exchanging routing information between gateway hosts (each with its own router) in a network of autonomous systems.
BGP have been designed to allow many kinds of routing policies to be enforced in the interAS traffic.

17. BGP – The Exterior Gateway Routing Protocol
Exterior gateway protocol routers have to worry about politics (security, billing, etc.)
BGP (Border Gateway Protocol) is essentially a distance vector protocol.
But keep track of entire path.
Discard the route through itself solve count-to-infinity.
Select route based on the distance (score). Any route violating polices has infinite score and is discarded as it pass F.

18. BGP – The Exterior Gateway Routing Protocol
(a) A set of BGP routers (b) Information sent to F.

19. Internet Multicating
IP supports multicasting, using class D addresses.
Two kinds of the group addresses are supported:
Permanent groups:
: all system on a LAN
: all routers on a LAN
: all OSPF routers on a LAN
: all designated OSPF routers on a LAN
Temporary groups must be created before used.
The query and response packets sent and received by multicast routers are called IGMP (Internet Group Management Protocol). It has two kinds of packets: query and response.
Multicasting routing is done using spanning tree.

20. Mobile IP How to send packets to a machine that is moving?
New IP address? Too much hassle.
Routers use complete IP address for routing:
Current routing is based on the network address.
The major goals of Mobile IP:
Each mobile host must be able to use its home IP address anywhere.
Software changes to the fixed hosts were not permitted.
Changes to the router software and tables were not permitted.
Most packets for mobile hosts should not make detours on the way.
No overhead should be incurred when a mobile host is at home.

21. Mobile IP Solution: Home agent, remote agent.
The remote agent tells the home agent the new location of the mobile station.
Packets go to home agent initially
Home agent tunnels the packets to the remote agent and informs the sources of the remote agent
the source sends (tunneling) directly to the remote agent.

22. What is IPv6?
IPv6 stands for "Internet Protocol Version 6“ and is also referred to as IPng (IP next generation).
IPv6 is the protocol designed by the IETF (The Internet Engineering Task Force) to replace the current version Internet Protocol, IP Version 4 (IPv4).
The core set of IPv6 protocols were made an IETF Draft Standard on August 10, 1998.
For more information about IPv6, refer to

23. Why is IPv6? More Addresses!
IP address allocation history:
1981 ~ IPv4 protocol published
1985 ~ 1/16 total space
1990 ~ 1/8 total space
1995 ~ 1/4 total space
2000 ~ 1/2 total space
More addresses are needed despite increasingly intense conservation efforts
CIDR (classless inter-domain routing)
PPP address sharing
NAT (network address translation)
Theoretical limit of 32-bit space: ~4 billion devices Practical limit of 32-bit space: ~250 million devices

24. IPv6 IPv6 major goals were:
Support billions of hosts, even with inefficient address space allocation.
Reduce the size of the routing tables.
Simplify the protocol, to allow routers to process packets faster.
Provide better security (authentication and privacy) than current IP.
Pay more attention to type of service, particularly for real-time data.
Aid multicasting by allowing scopes to be specified.
Make it possible for a host to roam without changing its address.
Allow the protocol to evolve in the future.
Permit the old and new protocols to coexist for years.

25. IPv6
SIPP (Simple Internet Protocol Plus) was selected and given the designation IPv6.
The main features of IPv6:
IPv6 has longer addresses than IPv4.
Improved header processing with better support for options and enhanced routing functionality
Auto-configuration
Better security support
Better support for Quality of Service (QoS)