[Network week5] Mobile IP, HoA, CoA, HA, FA, Routing, Intra-Domain Routing

makeitcloud·2020년 10월 16일

Computer Science

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Mobile IP

  • Extension of IP protocol
    : That allows mobile computer to be connected to the Internet at any location

Stationary and Mobile Hosts

  • Original IP addressing was based on the assumption that
    : A host is stationary, attached to one specific network
  • The address is valid only when the host is attached to the network
    : If the network changes, the address is no longer valid
  • Changing address
    : Let the mobile host change its address as it goes to the new network
  • 2 major drawbacks
    : Rebooting
    : If the host roams from one network to another during a transmission, the exchange will be interrupted
    This is because the ports and IP address of the client and the server must remain constant for the duration of the connection

2 Addresses

  • Home address (HoA) and care-of address(CoA)
    : Permanent address and a temporary address
    : Permanent address associates the host with its home network (HN)
    : When a host moves from one network to another, the CoA changes
    = It is associated with the foreign network (FN), the network to which the host moves


  • To make the change of address transparent to the rest of the Internet requires a home agent and a foreign agent
  • Shown the home and the foreign agents as routers
    : We need to emphasize that their specific function as an agent is perform in the application layer

HA and FA

  • Home agent(HA)
    : A router attached to HN
    : Acts on behalf of the mobile host when a remote host sends a packet to mobile host
  • Foreign agent(FA)
    : A router attached to FN
    : Foreign agent receives and delivers packets sent by the home agent to the mobile host

Data Transfer

  • From a remote host (RH) to HA
    : RH sends a packet as though MH is at its home network
    : Uses RH address as source and home address of mobile host as destination

  • From HA to FA
    : HA sends the packet to the foreign agent using the tunneling
    : HA encapsulates the whole IP packet inside another IP packet using its address as the source and the foreign agent's addres as the destination

  • From FA to MH
    : When FA receives the packet, it removes the original packet
    : Since DST address is home address of MH, FA consults a registry table to find the care-of Address of MH

  • From MH to RH
    : It sends as it does normally
    : MH prepares a packet with its home address as SRC, and the address of RH as DST


  • RH is unaware of any movement by MH
    : RH sends packet using home address of MH as DST
    : It receives packets that have home address of MH as SRC

Double crossing

  • Occurs when RH communicates with an MH that has moved to the same network as RH
  • When MH sends a packet to RH, there is no inefficiency
  • When RH sends a packet to MH, the packet crosses the Internet twice

Triangle Routing

  • Less severe
  • Occurs when RH communicates with MH that is not attached to the same as MH

Intra-Domain Routing

Routing and Forwarding

  • Main objective of network layer
    : Transport packets from source to destination
  • Two mechanisms are used in network layer
  1. Forwarding
    : Algorithm use by each router to determine on which interface each packet should be sent to reach its destination or follow its virtual circuit
    : Relies on the routing table maintained by each router
  2. Routing
    : Distributed algorithm that distributes to all routers the information that allows them to build their routing tables


  • How to build routing table of each router?
    : Include in the routing table of each router the path to allow it to reach each destination
  • Selection of the shortest paths
    : How does "C" choose a next-hop one the path towards host "H"?
    : Based on metrics
  1. Minimum hop
  2. Cost
  3. Delay
  4. 1/Throughput


  • An internet is a combination of networks connected by routers
  • A metric is a cost assigned for passing through a network
  • Total metric of a route is equal to the sum of metrics of networks that comprise route
  • Router chooses the route with the shortes (smallest) metric

Intra and Inter Domain Routing

  • Because Internet can be so large, one routing protocol cannot handle the task of updating routing tables of all routers
  • Internet is divided into autonomous systems(AS)
    : AS is a group of network and routers under authority of a single administration
  • Intra-domain routing
    : Used for routing inside an AS
  • Inter-domain
    : Used for routing between AS
  • A routing protocol is a combination of rules and procedures that lets routers in the Internet inform each other of changes

Intra-Domain Routing

Static Routing

  • Network manager computes all routing tables and downloads them on all routers
    : Shortest path algorithms
  • Advantages of static routing
    : Easy to use in small network
    : Routing tables can be optimized easily
  • Drawbacks of static routing
    : Does not adapt dynamically to network load
    : How to deal with link and router failures?

Dynamic or Distributed Routing

  • Routers exchange messages and use a distributed algorithm to build their routing tables
    : Used in almost all networks
  • Advantages
    : Can easily adapt routing tables to events
  • Drawbacks
    : More complex to implement than static routing
  • Most common distributed routing methods
  1. Distance vector routing
  2. Link state routing

Shortest Path Algorithms

  • Distance vector protocols
    -- Neighbors exchange list of distances to destinations
    -- Best next-hop determined for each destination
    -- Distributed Bellman-Ford algorithm
  • Link State Protocol
    -- Link state information flooded to all routers
    -- Routers have complete topology information
    -- Dijkstra's shortest first algorithm
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