Overview

1
Overview

• Last Lecture
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• Source chapter 15
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• Internet Protocols (3)
• Source chapter 15
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• Internet Protocols (4)
• Source chapter 15

2
CIDR

• Classless Interdomain Routing
• Address allocation problem
• Exhaustion of the class B network address space
• A class C network is normally two small for
  mid-size organizations
• Solution allocate contiguous blocks of class C
  networks
• Routing table problem
• By default, a routing table contains an entry for
  every network
• The entries for all class C networks are beyond
  the ability of the current software and hardware
  to manage
• Solution
• Divide the world into 8 regions and allocate the
  class C networks as below
• Multi-regional 192.0.0.0 - 193.255.255.255
• Europe 194.0.0.0 - 195. 255.255.255
• Others 196.0.0.0 - 197. 255.255.255
• North America 198.0.0.0 - 199. 255.255.255
• C/S America 200.0.0.0 - 201. 255.255.255
• Pacific rim 202.0.0.0 - 203. 255.255.255
• Others 204.0.0.0 - 205. 255.255.255
• Others 206.0.0.0 - 207. 255.255.255

3
CIDR

• Classless Interdomain routing
• Class C addresses become meaningless on the
  routes between the above domains
• The technique CIDR is used to route between
  domains without honoring class C addresses
• The key point is that multiple contiguous class C
  addresses are aggregated to be one entry in the
  routing table
• CIDR is also called supernetting in contrast to
  subnetting
• Example
• An organization has four class C addresses
• 194.0.32.0, 194.0.33.0, 194.0.34.0, 194.0.35.0
• We can use the following supernet mask to produce
  the network address of the group, which is no
  longer observe the rules of IP address classes

4
IP routing

• IP routes packets by using the IP network number
• If the network number is the local network, the
  destination is in the local network. Use a link
  layer frame to send to the destination
• Otherwise the destination is outside the local
  network. Use a link layer frame to send to a
  local router (gateway) which can choose a route
  and send the packet.
• Every host and router contains a routing table
• The table records which router to forward a
  packet and which data link connection can be used
  to reach the router
• Routing tables can be modified by
• Hand - static routing
• Routing protocol - dynamic routing
• ICMP - redirect
• Routing protocol
• Interior routing the daemon is called routed,
  which adopts Routing Information Protocol (RIP)
  running distance-vector routing algorithm for
  local networks
• Exterior routing the daemon is called gated,
  which adopts Open Shortest Path First (OSPF)
  running link state routing algorithm among
  gateways

5
DNS

• Domain Name System
• Converts IP names (ASCII strings) into IP
  addresses
• Back in ARPANET, there was simply a file,
  host.txt, that listed all the hosts and their IP
  addresses. The file was maintained by a server
  and fetched by all other hosts and routers
• For a few hundred machines, this approach worked
  reasonably well.
• For hundreds of thousands of workstations in
  Internet
• Using a single file will cause traffic overload,
  name collision, and consistency problems
• a hierarchical, domain-based naming scheme and a
  distributed database system are used to implement
  the DNS
• Map an IP name into an IP address
• Map an IP address into an IP name
• Provide email routing information
• Handle aliases

6
DNS

• Internet domain name space
• DNS name space is divided up into non-overlapping
  zones.
• Each zone contains some part of the tree and also
  contains name servers
• Each zone has at least one name server which
  maintains file containing IP names and addresses
  of all workstations in the zone
• DNS database is distributed among the name servers

7
DNS management

• Network Information Center (NIC) manages root and
  top level domain
• Local administration manages lower level domain
• A name server must contact other name servers for
  non-local IP addresses
• Root name server root-servers.net
• Provides the IP addresses for the name server
  authoritative for top level domain names
• e.g. domain edu has its name server
  edu-server.net
• 13 root name servers are currently available
• A name server has to know the IP address of one
  of them
• Domain name resolution
• If a host has a query about an IP name, it passes
  the query to one of the local name servers. If
  the IP name falls under the zone of the name
  server, it returns the IP address of the name to
  the host
• If, however, the IP name is remote and no
  information about the name is available, the name
  server sends a query message to the top-level
  name server for the name requested

8
DNS operation

• Example of domain name resolution
• For example, a host flits.cs.vu.nl wants to know
  the IP address of the host linda.cs.yale.edu
• flits.cs.vu.nl sends a query to the local name
  server cs.vu.nl
• Since linda.cs.yale.edu is a remote host and the
  server cs.vu.nl knows nothing about it, the
  server sends the query to the root name server
• The root name server forwards the query to the
  server of the edu domain, edu-server.net
• edu-server.net may not know linda.cs.yale.edu,
  but it at least knows its child yale.edu. So
  edu-server.net sends the query to the name
  server for yale.edu
• In turn, the name server for yale.edu forwards
  the query to the name server for cs.yale.edu
  which has the requested information and sends the
  answer hop by hop back to the originator
  flits.cs.vu.nl

9
BOOTPDHCP

• BOOTP DHCP
• BOOTstrap Protocol
• Dynamic Host Configuration Protocol
• DHCP is a successor to BOOTP
• Two bootstrap protocols that allow a host to
  determine its IP address without using RARP
• RARP operates at a low level and relies on
  hardware address. These limit server application
  and dynamic allocation of hardware addresses
• The protocols are based on high layer protocol
  UDP/IP
• BOOTP operation
• When a client machine bootstraps, it uses BOOTP
  to broadcast an UDP datagram to every machine in
  the local network, requesting bootstrap
  information, such as its IP address, file server
  IP address, router IP address, boot file name,
  and etc.
• When a server machine receives the request, its
  BOOTP sends a reply to the client using broadcast
• The client takes all responsibility for reliable
  communication by using timeout and retransmission

10
DHCP

• BOOTP was designed for a relatively static
  environment
• Each host has a permanent network connection
• A manager creates a BOOTP configuration file that
  specifies a set of BOOTP parameters for each
  host. The file does not change frequently
• With the advert of Internet Service Provider,
  wireless networks and portable computers,
  automatic allocation of IP addresses are needed
• DHCP operation
• A manage must configure a DHCP server by
  supplying a set of IP addresses
• DHCP allows manual allocation, permanent
  automatic allocation, and temporary automatic
  allocation of IP addresses
• Automatic allocation is subject to administrative
  constraints
• Hardware address of a client is used as its ID
• A client needs to exchange messages with the
  server to negotiate use of an IP address, such as
  the lease time of the address
• A client can acquire all configuration info in a
  single message

11
Mobile IP

• Problem
• How to route a packet to a mobile host
• Two kinds of users
• Migratory users stationary users who move from
  one fixed site to another from time to time but
  use the network only when they are physically
  connected to it
• Roaming users compute on the run and want to
  maintain their connections as they move around.
• Mobile IP is for the migratory users
• A mobile host has two addresses
• Primary address permanent and fixed
• Second address temporary and change from
  location to location
• How to find the mobile host?
• The world is divided into small areas
• Each area has a home agent, which keeps track of
  users whose home is in the area
• Each area has one or more foreign agents, which
  keep track of all mobile users visiting the area
• When a new user enters an area, his computer must
  register itself with the foreign agent there, so
  that the foreign agent can inform its home agent
  where it is

12
Mobile IP

• How to send a packet to a mobile host?
• When a packet is sent to a mobile host, it is
  routed to its home agent in the first place
• Because the home agent knows the address of the
  hosts foreign agent, it forwards the packet to
  the foreign agent which then passes the packet to
  the mobile host
• Then the hosts home agent tells the sender to
  henceforth send packets to the hosts foreign
  agent, instead of sending to the home agent
• Then subsequent packets can now be routed
  directly to the mobile host via the foreign
  agent, by passing the home location entirely

13
Voice and Video over IP

• Additional protocol support is required when
  sending real-time data over IP
• RTP
• Real-Time Transport Protocol
• Provides two key facilities
• A sequence number in each packet that allows a
  receiver to detect out-of-order delivery or loss
• A timestamp that allows a receiver to control
  playback
• IP telephony
• H.323 Standards proposed by ITU
• Session Initiation Protocol (SIP) proposed for
  signaling by IETF
• RSVP
• Resource ReserVation Protocol
• An endpoint uses RSVP to request a simplex flow
  through an IP Internet with specified QoS bounds.
• If routers along the path agree to honor the
  request, they approve it otherwise, they deny it
• If an application needs QoS in two directions
  (full duplex), each endpoint must use RSVP to
  request a separate flow

14
Summary

• Classless Interdomain Routing
• Supernetting
• IP routing
• Static routing
• Dynamic routing
• Bellman-Ford algorithm (RIP)
• Link state algorithm (OSPF)
• ICMP - redirect
• Domain Name System
• BOOTP DHCP
• Mobile IP
• Multimedia applications over IP
• IP phone