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					      ICMP: Internet Control Message
                 Protocol
• used by hosts, routers,
                                  Type   Code   description
  gateways to communication       0      0      echo reply (ping)
  network-level information       3      0      dest. network unreachable
   – error reporting:             3      1      dest host unreachable
     unreachable host, network,   3      2      dest protocol unreachable
     port, protocol               3      3      dest port unreachable
                                  3      6      dest network unknown
   – echo request/reply (used     3      7      dest host unknown
     by ping)                     4      0      source quench (congestion
• network-layer “above” IP:                     control - not used)
   – ICMP msgs carried in IP      8      0      echo request (ping)
                                  9      0      route advertisement
     datagrams
                                  10     0      router discovery
• ICMP message: type, code        11     0      TTL expired
  plus first 8 bytes of IP        12     0      bad IP header
  datagram causing error
  DHCP: Dynamic Host Configuration
            Protocol
Goal: allow host to dynamically obtain its IP
 address from network server when it joins
 network
  Can renew its lease on address in use
  Allows reuse of addresses (only hold address while
    connected an “on”
  Support for mobile users who want to join network
    (more shortly)
DHCP overview:
  – host broadcasts “DHCP discover” msg
  – DHCP server responds with “DHCP offer”
DHCP client-server scenario

   A    223.1.1.1          DHCP            223.1.2.1
                           server
         223.1.1.2
               223.1.1.4    223.1.2.9
   B
                                    223.1.2.2          arriving DHCP
       223.1.1.3    223.1.3.27                  E      client needs
                                                       address in this
        223.1.3.1                223.1.3.2
                                                       network
DHCP client-server scenario
 DHCP server: 223.1.2.5                                         arriving
                                 DHCP discover
                                                                 client
                                  src : 0.0.0.0, 68
                                  dest.: 255.255.255.255,67
                                  yiaddr: 0.0.0.0
                                  transaction ID: 654

                                   DHCP offer
                                    src: 223.1.2.5, 67
                                    dest: 255.255.255.255, 68
                                    yiaddrr: 223.1.2.4
                                    transaction ID: 654
                                    Lifetime: 3600 secs
             DHCP request
               src: 0.0.0.0, 68
               dest:: 255.255.255.255, 67
               yiaddrr: 223.1.2.4
               transaction ID: 655
     time      Lifetime: 3600 secs

                                  DHCP ACK
                                    src: 223.1.2.5, 67
                                    dest: 255.255.255.255, 68
                                    yiaddrr: 223.1.2.4
                                    transaction ID: 655
                                    Lifetime: 3600 secs
               What is mobility?
• spectrum of mobility, from the network
  perspective:
no mobility                                   high mobility




mobile user, using   mobile user,    mobile user, passing
same access point    connecting/     through multiple
                     disconnecting   access point while
                     from network    maintaining ongoing
                     using DHCP.     connections (like cell
                                     phone)
                  Mobility: Vocabulary
   home network: permanent     home agent: entity that will
   “home” of mobile            perform mobility functions on
   (e.g., 128.119.40/24)
                               behalf of mobile, when mobile
                               is remote




                                wide area
                                network
Permanent address:
address in home
network, can always be
used to reach mobile
e.g., 128.119.40.186         correspondent
    Mobility: more vocabulary
                                                 visited network: network
         Permanent address: remains              in which mobile currently
         constant (e.g., 128.119.40.186)         resides (e.g., 79.129.13/24)

                   Care-of-address: address
                   in visited network.
                   (e.g., 79,129.13.2)


                                     wide area
                                     network

                                                         home agent: entity in
                                                         visited network that
                                                         performs mobility
correspondent: wants                                     functions on behalf
to communicate with                                      of mobile.
mobile
  How do you contact a mobile friend:

                               I wonder where
Consider friend frequently
                               Alice moved to?
  changing addresses, how do
• you findall phone
  search her?
  books?
• call her parents?
• expect her to let you
  know where he/she
  is?
       Mobility: approaches
• Let routing handle it: routers advertise
  permanent address of mobile-nodes-in-
  residence via usual routing table exchange.
   – routing tables indicate where each mobile
     located
   – no changes to end-systems
• Let end-systems handle it:
   – indirect routing: communication from
     correspondent to mobile goes through home
     agent, then forwarded to remote
   – direct routing: correspondent gets foreign
       Mobility: approaches
• Let routing handle it: routers advertise
                       not
  permanent address of mobile-nodes-in-
                     scalable
  residence via usual routing table exchange.
                   to millions of
                      mobiles
   – routing tables indicate where each mobile
     located
   – no changes to end-systems
• let end-systems handle it:
   – indirect routing: communication from
     correspondent to mobile goes through home
     agent, then forwarded to remote
   – direct routing: correspondent gets foreign
        Mobility: registration
                                       visited network
    home network


                                               1
                        2
                     wide area
                     network

                                             mobile contacts
         foreign agent contacts home         foreign agent on
         agent home: “this mobile is         entering visited
         resident in my network”             network


End result:
• Foreign agent knows about mobile
• Home agent knows location of mobile
       Mobility via Indirect Routing
                                            foreign agent
                                            receives packets,
                home agent intercepts       forwards to mobile
                packets, forwards to                             visited
                foreign agent                                    network
home
network
                                                           3
                               wide area
                               network
                                        2
                        1
   correspondent                                    4
   addresses packets
                                                        mobile replies
   using home address
                                                        directly to
   of mobile
                                                        correspondent
     Indirect Routing: comments
• Mobile uses two addresses:
   – permanent address: used by correspondent
      (hence mobile location is transparent to
      correspondent)
   – care-of-address: used by home agent to
      forward datagrams to mobile
• foreign agent functions may be done by mobile
  itself
• triangle routing: correspondent-home-network-
  mobile
   – inefficient when
         Forwarding datagrams to remote
                     mobile
                                                 foreign-agent-to-mobile packet
      packet sent by home agent to foreign          dest: 128.119.40.186
      agent: a packet within a packet

      dest: 79.129.13.2   dest: 128.119.40.186




Permanent address:
128.119.40.186

                                                            Care-of address:
                                                                 79.129.13.2
           dest: 128.119.40.186
           packet sent by
           correspondent
   Indirect Routing: moving between
               networks
• suppose mobile user moves to another
  network
  – registers with new foreign agent
  – new foreign agent registers with home agent
  – home agent update care-of-address for
    mobile
  – packets continue to be forwarded to mobile
    (but with new care-of-address)
• Mobility, changing foreign networks
  transparent: on going connections can be
  maintained!
          Mobility via Direct Routing
                                             foreign agent
                                             receives packets,
                 correspondent forwards      forwards to mobile
                 to foreign agent                                 visited
                                                                  network
home
network                                                     4
                                 wide area
                         2       network
                                             3
   correspondent             1                       4
   requests, receives
                                                         mobile replies
   foreign address of
                                                         directly to
   mobile
                                                         correspondent
Mobility via Direct Routing: comments
• overcome triangle routing problem
• non-transparent to correspondent:
  correspondent must get care-of-address
  from home agent
  – What happens if mobile changes networks?
                 Mobile IP
• RFC 3220
• has many features we’ve seen:
  – home agents, foreign agents, foreign-agent
    registration, care-of-addresses, encapsulation
    (packet-within-a-packet)
• three components to standard:
  – agent discovery
  – registration with home agent
  – indirect routing of datagrams
        Mobile IP: agent discovery
  • agent advertisement: foreign/home agents
    advertise service by broadcasting ICMP
    messages (typefield 8= 9) 16
                 0                24

                       type = 9     code = 0            checksum
                                    =9                  =9
H,F bits: home                                                             standard
and/or foreign agent                   router address                     ICMP fields


R bit: registration
required               type = 16     length         sequence #
                                                 RBHFMGV
                        registration lifetime                 reserved
                                                   bits                  mobility agent
                                                                         advertisement
                                  0 or more care-of-                       extension

                                      addresses
  Mobile IP: registration example
                                                                  visited network: 79.129.13/24
  home agent          foreign agent
HA: 128.119.40.7     COA: 79.129.13.2      ICMP agent adv.
                                                                                Mobile agent
                                            COA: 79.129.13.2                  MA: 128.119.40.186
                                            ….

                                           registration req.
                   registration req.        COA: 79.129.13.2
                    COA: 79.129.13.2        HA: 128.119.40.7
                    HA: 128.119.40.7        MA: 128.119.40.186
                    MA: 128.119.40.186      Lifetime: 9999
                    Lifetime: 9999          identification:714
                    identification: 714     ….
                    encapsulation format
                    ….



                   registration reply
           time     HA: 128.119.40.7       registration reply
                    MA: 128.119.40.186
                    Lifetime: 4999          HA: 128.119.40.7
                    Identification: 714     MA: 128.119.40.186
                    encapsulation format    Lifetime: 4999
                    ….                      Identification: 714
                                            ….

				
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