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1 hapter 4 Network Layer note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR ll material copyright J.F Kurose and K.W. Ross, ll Rights Reserved omputer Networking: Top Down pproach Featuring the Internet, nd edition. Jim Kurose, Keith Ross ddison-wesley, July 00. Network Layer 4- hapter 4: Network Layer : : : IPv6, : : IP intra-domain inter-domain IPv6 Network Layer 4- hapter The Internet (IP) IPv : : : : application transport data link data link data link data link data link data link data link data link data link application transport data link Network Layer 4-3 Network Layer 4-4 Q: :???? Network Layer 4-5 Network Layer 4-6

2 TM, frame-relay,.5 : application transport data link 5. Data flow begins 6. Receive data 4. all connected 3. ccept call. Initiate call. incoming call application transport data link application transport data link application transport. Send data. Receive data data link Network Layer 4-7 Network Layer 4-8 :TM Network rchitecture Internet TM TM TM TM Service Model best effort R VR R UR andwidth none constant rate guaranteed rate guaranteed minimum none Guarantees? Loss Order Timing no yes yes no no no yes yes yes yes : Intserv, Diffserv no yes yes no no ongestion feedback no (inferred via loss) no congestion no congestion yes no Network Layer 4-9 : TM : dumb Network Layer 4-0 hapter Link state routing Distance vector routing The Internet (IP) IPv Network Layer 4- : : 5 D 3 3 : 5 F Network Layer 4-

3 : : : : Dijkstra k k : c(i,j): i j D(v): V p(v): v v v N: Network Layer 4-3 Network Layer 4-4 Dijsktra Dijkstra : Initialization: N = {} 3 for all nodes v 4 if v adjacent to 5 then D(v) = c(,v) 6 else D(v) = infinity 7 8 Loop 9 find w not in N such that D(w) is a minimum 0 add w to N update D(v) for all v adjacent to w and not in N: D(v) = min( D(v), D(w) + c(w,v) ) 3 /* new cost to v is either old cost to v or known 4 shortest path cost to w plus cost from w to v */ 5 until all nodes in N Network Layer 4-5 Step start N D D D D DF D(),p(),,, D(),p() D(D),p(D) 5,, 4,D 3, 3, 5 D F D(),p() infinity,d D(F),p(F) infinity infinity 4, 4, 4, Network Layer 4-6 Dijkstra : n N w n*(n+)/ : O(n**) : O(nlogn) : = +e D e e initially +e 0 D +e 0 0 recompute routing 0 +e D 0 0 +e recompute +e 0 D +e 0 e recompute Network Layer 4-7 : : : / : Z Y D (Y,Z) Z = Y Z = c(,z) + min {D (Y,w)} w Network Layer 4-8 3

4 7 D (,D) D (,D) D (,) 8 D D c(,d) + min {D (,w)} w = = + = 4 D c(,d) + min {D (,w)} w = = +3 = 5 loop! = c(,) + min {D (,w)} w = 8+6 = 4 loop! cost to destination via D () D destination D Network Layer 4-9 cost to destination via D () D destination D Distance table destination D Outgoing link to use, cost, D,5 D,4 D,4 Routing table Network Layer 4-0 : : : : : ( ) Network Layer 4- : Initialization: for all adjacent nodes v: 3 D (*,v) = infinity /* the * operator means "for all rows" */ 4 D (v,v) = c(,v) 5 for all destinations, y 6 send min D (y,w) to each neighbor /* w over all 's neighbors */ w Network Layer 4- : 8 loop 9 wait (until I see a link cost change to neighbor V 0 or until I receive update from neighbor V) if (c(,v) changes by d) 3 /* change cost to all dest's via neighbor v by d */ 4 /* note: d could be positive or negative */ 5 for all destinations y: D (y,v) = D (y,v) + d 6 7 else if (update received from V wrt destination Y) 8 /* shortest path from V to some Y has changed */ 9 /* V has sent a new value for its min wdv(y,w) */ 0 /* call this received new value is "newval" */ for the single destination y: D (Y,V) = c(,v) + newval 3 if we have a new min w D (Y,w)for any destination Y 4 send new value of min w D (Y,w) to all neighbors 5 6 forever Network Layer 4-3 Y 7 Z Network Layer 4-4 4

5 Y 7 Z Z D (Y,Z) = c(,z) + min {D (Y,w)} w = 7+ = 8 Y D (Z,Y) = c(,y) + min {D (Z,w)} w = + = 3 : 4 Y 50 Z algorithm terminates Network Layer 4-5 Network Layer 4-6 poisoned reverse : - count to infinity 60 4 Y 50 Z Z Y : Z Y Z Y Z count to infinity 60 4 Y 50 Z algorithm continues on! algorithm terminates Network Layer 4-7 Network Layer 4-8 LS: n, O(n) DV: LS: O(n ) O(n) DV: count-to-infinity : LS: DV: DV Network Layer 4-9 hapter The Internet (IP) IPv Network Layer

6 : : S: utonomous System S intra-s S intra-s S S intra-s S inter-s Network Layer 4-3 Network Layer 4-3 Intra-S Inter-S Intra-S Inter-S a.b b d.a a b.c inter-s, intra-s.c c.a a c : inter-s b S intra-s Inter-S.b routing between.a and b a.c a Host d h c b Intra-S routing within S.a Host c h a b Intra-S routing within S inter-s intra-s Network Layer 4-33 Network Layer 4-34 hapter 4 roadmap 4. Introduction and Network Service Models 4. Routing Principles 4.3 Hierarchical Routing 4.4 The Internet (IP) Protocol 4.4. IPv4 addressing 4.4. Moving a datagram from source to destination Datagram format IP fragmentation IMP: Internet ontrol Message Protocol DHP: Dynamic Host onfiguration Protocol NT: Network ddress Translation 4.5 Routing in the Internet 4.6 What s Inside a Router 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility Network Layer 4-35 hapter The Internet (IP) 4.4. IPv Datagram IP IMP: Internet ontrol Message Protocol DHP: Dynamic Host onfiguration Protocol NT: Network ddress Translation IPv Network Layer

7 : Network layer Routing protocols path selection RIP, OSPF, GP Transport layer: TP, UDP forwarding table Link layer layer IP protocol addressing conventions datagram format packet handling conventions IMP protocol error reporting router signaling Network Layer 4-37 IP : IP : 3 : / IP = Network Layer 4-38 IP IP 3... IP : IP IP LN IP Network Layer 4-39 Network Layer 4-40 IP class D 0 host 0 host 0 host 0 multicast address 3 bits to to to to Network Layer 4-4 IP : IDR : IDR: lassless InterDomain Routing a.b.c.d/x x host part part /3 Network Layer 4-4 7

8 IP Q: IP Wintel: control-panel->->configuration- >tcp/ip->properties UNI: /etc/rc.config DHP: Dynamic Host onfiguration Protocol: plug-and-play IP Q: IP : ISP ISP's block /0 Organization /3 Organization /3 Organization / Organization /3 Network Layer 4-43 Network Layer 4-44 ISPs-R-Us Organization Organization 0 Organization / /3 Organization /3 Organization /3.... Organization /3 Fly-y-Night-ISP ISPs-R-Us / /6 Internet Organization /3 Organization /3 Organization /3.. Fly-y-Night-ISP ISPs-R-Us / / /3 Internet Network Layer 4-45 Network Layer 4-46 IP Q: ISP : INN: Internet orporation for ssigned Names and Numbers DNS IP datagram: misc fields source IP addr dest IP addr data forwarding table in Dest. Net. next router Nhops Network Layer 4-47 Network Layer

9 misc fields data IP : forwarding table in Dest. Net. next router Nhops Network Layer 4-49 misc fields data forwarding table in Dest. Net. next router Nhops Network Layer 4-50 forwarding table in router misc fields data Dest. Net router Nhops interface Network Layer 4-5 IP IP protocol version number header length (bytes) type of data max number remaining hops (decremented at each router) upper layer protocol to deliver payload to TP 0 bytes of TP 0 bytes of IP = 40 bytes + app layer overhead 3 bits ver head. type of len service length 6-bit identifier flgs fragment offset time to upper Internet live layer checksum 3 bit source IP address 3 bit destination IP address Options (if any) data (variable length, typically a TP or UDP segment) total datagram length (bytes) for fragmentation/ reassembly.g. timestamp, record route taken, specify list of routers to visit. Network Layer 4-5 IP IP MTU: max.transfer size MTU IP IP reassembly fragmentation: in: one large datagram out: 3 smaller datagrams 4000 MTU = 500 bytes length =4000 ID =x fragflag =0 offset =0 length =500 length =500 length =040 ID =x ID =x ID =x fragflag = offset =0 fragflag offset = =480 fragflag offset =0 =960 Network Layer 4-53 Network Layer

10 IMP: Internet ontrol Message Protocol DHP: Dynamic Host onfiguration Protocol ping IP IMP IP IMP : IP Type ode description 0 0 echo reply (ping) 3 0 dest. unreachable 3 dest host unreachable 3 dest protocol unreachable 3 3 dest port unreachable 3 6 dest unknown 3 7 dest host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 0 0 router discovery 0 TTL expired 0 bad IP header : IP DHP : DHP discover DHP DHP offer IP : DHP request DHP : DHP ack Network Layer 4-55 Network Layer 4-56 DHP DHP server arriving DHP client needs address in this DHP DHP server: time DHP discover src : , 68 dest.: ,67 yiaddr: transaction ID: 654 DHP offer src: 3...5, 67 dest: , 68 yiaddrr: transaction ID: 654 Lifetime: 3600 secs DHP request src: , 68 dest:: , 67 yiaddrr: transaction ID: 655 Lifetime: 3600 secs arriving client DHP K src: 3...5, 67 dest: , 68 yiaddrr: transaction ID: 655 Lifetime: 3600 secs Network Layer 4-57 Network Layer 4-58 NT: Network ddress Translation NT: Network ddress Translation rest of Internet NT IP local (e.g., home ) 0.0.0/ /4 : IP ISP - IP ISP Network Layer 4-59 Network Layer

11 NT: Network ddress Translation : NT : : IP NT IP... NT IP IP NT IP NT incoming datagrams: replace NT IP NT IP Network Layer 4-6 NT: Network ddress Translation : NT router changes datagram source addr from , 3345 to , 500, updates table NT translation table WN side addr LN side addr , , 3345 S: , 500 D: , S: , 80 D: , : Reply arrives dest. address: , S: , 3345 D: , 80 S: , 80 D: , : host sends datagram to , : NT router changes datagram dest addr from , 500 to , 3345 Network Layer 4-6 NT: Network ddress Translation 6 60,000 NT : 3 NT PP IPv6 Network Layer 4-63 hapter The Internet (IP) Intra-S : RIP OSPF 4.5. Inter-S : GP IPv Network Layer 4-64 S: utonomous Systems Stub S: : S Multihomed S: : S Transit S: S Intra-S: Inter-S: inter-s : GP Network Layer 4-65 S Intra-S border (exterior gateway) routers Inter-S interior (gateway) routers Network Layer 4-66

12 Intra-S RIP ( Routing Information Protocol) Interior Gateway Protocols (IGP) Intra-S : RIP: Routing Information Protocol OSPF: Open Shortest Path First IGRP: Interior Gateway Routing Protocol (isco ) 98 SD-UNI : 5 : 30Response Message ( advertisement ) 5 Network Layer 4-67 Network Layer 4-68 RIP: w x y D z RIP: Dest Next hops w - - x - - z D w x y D z Routing table in D Destination Network Next Router Num. of hops to dest. w y z 7 x Network Layer 4-69 Destination Network Next Router Num. of hops to dest. w y z 7 5 x Routing table in D Network Layer 4-70 RIP: 80 = 6 Network Layer 4-7 RIP RIP route-d UDP routed Transprt (UDP) forwarding (IP) table link forwarding table routed Transprt (UDP) (IP) link Network Layer 4-7

13 RIP Router: giroflee.eurocom.fr Destination Gateway Flags Ref Use Interface UH lo U 3 fa U le U 5 qaa U 3 0 le0 default UG LN LN Network Layer 4-73 OSPF (Open Shortest Path First) open : LS Dijkstra OSPF S TP UDP IP ISPF Network Layer 4-74 OSPF RIP OSPF : OSPF RIP TOS : OSPF (MOSPF) OSPF OSPF Network Layer 4-75 Network Layer 4-76 OSPF inter-s : GP : OSPF S R5 S (RIP intra-s routing) R GP R R3 GP S (OSPF intra-s routing) Figure 4.5.-new: GP use for inter-domain routing R4 S3 (OSPF intra-s routing) Network Layer 4-77 Network Layer

14 inter-s : GP GP (order Gateway Protocol): : order Gateway S GP (S) Z Path (,Z) =,Y,Y,Y3,,Z Network Layer 4-79 inter-s : GP : W W S W Path (W,Z) = w, Path (,Z) : Z Z Network Layer 4-80 GP: GP: W legend: provider customer : W legend: provider customer : Y Y Figure 4.5-GPnew: a simple GP scenario,, :,W,Y: Network Layer 4-8 Figure 4.5-GPnew: a simple GP scenario W W W W W w Network Layer 4-8 GP Q: GP GP GP TP GP OPN: TP UPDT: KPLIV: UPDT ; OPN K NOTIFITION: Network Layer 4-83 Network Layer

15 Intra- Inter-S : Inter-S: Intra-S: : : Intra-S: Inter-S: hapter The Internet (IP) IPv Network Layer 4-85 Network Layer 4-86 : (RIP, OSPF, GP) : : e.g., thernet 5 : Network Layer 4-87 Network Layer (HOL) : Network Layer 4-89 Network Layer

16 : PU Input Port Memory Output Port System us : Gbps bus, isco 900: : isco atalyst 8500 Network Layer 4-9 Network Layer 4-9 : isco 000: 60 Gbps FIFO Network Layer 4-93 Network Layer 4-94 hapter 4 roadmap 4. Introduction and Network Service Models 4. Routing Principles 4.3 Hierarchical Routing 4.4 The Internet (IP) Protocol 4.5 Routing in the Internet 4.6 What s Inside a Router? 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility Network Layer 4-95 Network Layer

17 IPv6 Initial motivation: 3-bit address space completely allocated by 008. dditional motivation: header format helps speed processing/forwarding header changes to facilitate QoS new anycast address: route to best of several replicated servers IPv6 datagram format: fixed-length 40 byte header no fragmentation allowed IPv6 Header (ont) Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same flow. (concept of flow not well defined). Next header: identify upper layer protocol for data Network Layer 4-97 Network Layer 4-98 Other hanges from IPv4 hecksum: removed entirely to reduce processing time at each hop Options: allowed, but outside of header, indicated by Next Header field IMPv6: new version of IMP additional message types, e.g. Packet Too ig multicast group management functions Transition From IPv4 To IPv6 Not all routers can be upgraded simultaneous no flag days How will the operate with mixed IPv4 and IPv6 routers? Two proposed approaches: Dual Stack: some routers with dual stack (v6, v4) can translate between formats Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers Network Layer 4-99 Network Layer 4-00 Dual Stack pproach D F Tunneling Logical view: tunnel F IPv6 IPv6 IPv6 IPv6 IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 Flow: Src: Dest: F data -to-: IPv6 Src: Dest: F data -to-: IPv4 Src: Dest: F data -to-: IPv4 Flow:?? Src: Dest: F data -to-: IPv6 Physical view: D F IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 Flow: Src: Dest: F data Src: Dest: Flow: Src: Dest: F Src: Dest: Flow: Src: Dest: F Flow: Src: Dest: F data data data Network Layer 4-0 -to-: IPv6 -to-: IPv6 inside IPv4 -to-: IPv6 inside IPv4 -to-f: IPv6 Network Layer 4-0 7

18 hapter 4 roadmap 4. Introduction and Network Service Models 4. Routing Principles 4.3 Hierarchical Routing 4.4 The Internet (IP) Protocol 4.5 Routing in the Internet 4.6 What s Inside a Router? 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility hapter The Internet (IP) IPv Network Layer 4-03 Network Layer 4-04 Multicast: one sender to many receivers Multicast: act of sending datagram to multiple receivers with single transmit operation analogy: one teacher to many students Question: how to achieve multicast Multicast: one sender to many receivers Multicast: act of sending datagram to multiple receivers with single transmit operation analogy: one teacher to many students Question: how to achieve multicast routers forward unicast datagrams Multicast via unicast source sends N unicast datagrams, one addressed to each of N receivers multicast receiver (red) not a multicast receiver (red) Network Layer 4-05 Multicast routers (red) duplicate and forward multicast datagrams Network multicast Router actively participate in multicast, making copies of packets as needed and forwarding towards multicast receivers Network Layer 4-06 Multicast: one sender to many receivers Multicast: act of sending datagram to multiple receivers with single transmit operation analogy: one teacher to many students Question: how to achieve multicast pplication-layer multicast end systems involved in multicast copy and forward unicast datagrams among themselves Internet Multicast Service Model multicast group multicast group concept: use of indirection hosts addresses IP datagram to multicast group routers forward multicast datagrams to hosts that have joined that multicast group Network Layer 4-07 Network Layer

19 Multicast groups class D Internet addresses reserved for multicast: host group semantics: o anyone can join (receive) multicast group o anyone can send to multicast group o no -layer identification to hosts of members needed: infrastructure to deliver mcast-addressed datagrams to all hosts that have joined that multicast group Joining a mcast group: two-step process local: host informs local mcast router of desire to join group: IGMP (Internet Group Management Protocol) wide area: local router interacts with other routers to receive mcast datagram flow many protocols (e.g., DVMRP, MOSPF, PIM) IGMP wide-area multicast routing IGMP Network Layer 4-09 IGMP Network Layer 4-0 IGMP: Internet Group Management Protocol host: sends IGMP report when application joins mcast group IP_DD_MMRSHIP socket option host need not explicitly unjoin group when leaving router: sends IGMP query at regular intervals host belonging to a mcast group must reply to query query report Network Layer 4- IGMP IGMP version router: Host Membership Query msg broadcast on LN to all hosts host: Host Membership Report msg to indicate group membership randomized delay before responding implicit leave via no reply to Query RF IGMP v: additions include group-specific Query Leave Group msg last host replying to Query can send explicit Leave Group msg router performs groupspecific query to see if any hosts left in group RF 36 IGMP v3: under development as Internet draft Network Layer 4- Multicast Routing: Problem Statement Goal: find a tree (or trees) connecting routers having local mcast group members tree: not all paths between routers used source-based: different tree from each sender to rcvrs shared-tree: same tree used by all group members pproaches for building mcast trees pproaches: source-based tree: one tree per source shortest path trees reverse path forwarding group-shared tree: group uses one tree minimal spanning (Steiner) center-based trees we first look at basic approaches, then specific protocols adopting these approaches Shared tree Source-based trees 9

20 Shortest Path Tree mcast forwarding tree: tree of shortest path routes from source to all receivers Dijkstra s algorithm S: source R R3 R 3 4 R6 R4 6 R7 5 R5 LGND i router with attached group member router with no attached group member link used for forwarding, i indicates order link added by algorithm Reverse Path Forwarding rely on router s knowledge of unicast shortest path from it to sender each router has simple forwarding behavior: if (mcast datagram received on incoming link on shortest path back to center) then flood datagram onto all outgoing links else ignore datagram Reverse Path Forwarding: example S: source R R3 R R6 R4 R7 R5 LGND router with attached group member router with no attached group member datagram will be forwarded datagram will not be forwarded result is a source-specific reverse SPT may be a bad choice with asymmetric links Reverse Path Forwarding: pruning forwarding tree contains subtrees with no mcast group members no need to forward datagrams down subtree prune msgs sent upstream by router with no downstream group members S: source R R3 R R6 P R4 P R7 R5 LGND P router with attached group member router with no attached group member prune message links with multicast forwarding Shared-Tree: Steiner Tree Steiner Tree: minimum cost tree connecting all routers with attached group members problem is NP-complete excellent heuristics exists not used in practice: computational complexity information about entire needed monolithic: rerun whenever a router needs to join/leave enter-based trees single delivery tree shared by all one router identified as center of tree to join: edge router sends unicast join-msg addressed to center router join-msg processed by intermediate routers and forwarded towards center join-msg either hits existing tree branch for this center, or arrives at center path taken by join-msg becomes new branch of tree for this router 0

21 enter-based trees: an example Suppose R6 chosen as center: R3 R R 3 R6 R4 R7 R5 LGND router with attached group member router with no attached group member path order in which join messages generated Internet Multicasting Routing: DVMRP DVMRP: distance vector multicast routing protocol, RF075 flood and prune: reverse path forwarding, source-based tree RPF tree based on DVMRP s own routing tables constructed by communicating DVMRP routers no assumptions about underlying unicast initial datagram to mcast group flooded everywhere via RPF routers not wanting group: send upstream prune msgs DVMRP: continued soft state: DVMRP router periodically ( min.) forgets branches are pruned: mcast data again flows down unpruned branch downstream router: reprune or else continue to receive data routers can quickly regraft to tree following IGMP join at leaf odds and ends commonly implemented in commercial routers Mbone routing done using DVMRP Tunneling Q: How to connect islands of multicast routers in a sea of unicast routers? topology logical topology mcast datagram encapsulated inside normal (non-multicastaddressed) datagram normal IP datagram sent thru tunnel via regular IP unicast to receiving mcast router receiving mcast router unencapsulates to get mcast datagram PIM: Protocol Independent Multicast not dependent on any specific underlying unicast routing algorithm (works with all) two different multicast distribution scenarios : Dense: group members densely packed, in close proximity. bandwidth more plentiful Sparse: # s with group members small wrt # interconnected s group members widely dispersed bandwidth not plentiful onsequences of Sparse-Dense Dichotomy: Dense Sparse: group membership by no membership until routers assumed until routers explicitly join routers explicitly prune receiver- driven data-driven construction construction of mcast on mcast tree (e.g., RPF) tree (e.g., center-based) bandwidth and nongroup-router processing router processing bandwidth and non-group- profligate conservative

22 PIM- Dense Mode PIM - Sparse Mode flood-and-prune RPF, similar to DVMRP but underlying unicast protocol provides RPF info for incoming datagram less complicated (less efficient) downstream flood than DVMRP reduces reliance on underlying routing algorithm has protocol mechanism for router to detect it is a leaf-node router center-based approach router sends join msg to rendezvous point (RP) intermediate routers update state and forward join after joining via RP, router can switch to source-specific tree increased performance: less concentration, shorter paths R3 R R join join all data multicast from rendezvous point R6 join R4 R5 R7 rendezvous point PIM - Sparse Mode hapter 4 roadmap sender(s): unicast data to RP, which distributes down RP-rooted tree RP can extend mcast tree upstream to source RP can send stop msg if no attached receivers no one is listening! R3 R R join join all data multicast from rendezvous point R6 join R4 R5 R7 rendezvous point 4. Introduction and Network Service Models 4. Routing Principles 4.3 Hierarchical Routing 4.4 The Internet (IP) Protocol 4.5 Routing in the Internet 4.6 What s Inside a Router? 4.7 IPv6 4.8 Multicast Routing 4.9 Mobility Network Layer 4-30 hapter 4 What is mobility? The Internet (IP) IPv spectrum of mobility, from the perspective: no mobility mobile user, using same access point mobile user, connecting/ disconnecting from using DHP. high mobility mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) Network Layer 4-3 Network Layer 4-3

23 Mobility: Vocabulary Mobility: more vocabulary home : permanent home of mobile (e.g., /4) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote Permanent address: remains constant (e.g., ) are-of-address: address in visited. (e.g., 79,9.3.) visited : in which mobile currently resides (e.g., /4) Permanent address: address in home, can always be used to reach mobile e.g., wide area correspondent Network Layer 4-33 correspondent: wants to communicate with mobile wide area home agent: entity in visited that performs mobility functions on behalf of mobile. Network Layer 4-34 How do you contact a mobile friend: Mobility: approaches onsider friend frequently changing addresses, how do you find her? search all phone books? call her parents? expect her to let you know where he/she is? I wonder where lice moved to? 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 address of mobile, sends directly to mobile Network Layer 4-35 Network Layer 4-36 Mobility: approaches Mobility: registration Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence not via usual routing table exchange. scalable to millions of routing tables indicate mobiles 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 address of mobile, sends directly to mobile Network Layer 4-37 home wide area foreign agent contacts home agent home: this mobile is resident in my nd result: Foreign agent knows about mobile Home agent knows location of mobile visited mobile contacts foreign agent on entering visited Network Layer

24 Mobility via Indirect Routing home correspondent addresses packets using home address of mobile home agent intercepts packets, forwards to foreign agent wide area foreign agent receives packets, forwards to mobile 4 3 visited mobile replies directly to 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-mobile inefficient when correspondent, mobile are in same Network Layer 4-39 Network Layer 4-40 Forwarding datagrams to remote mobile Indirect Routing: moving between s packet sent by home agent to foreign agent: a packet within a packet dest: dest: Permanent address: dest: packet sent by correspondent foreign-agent-to-mobile packet dest: are-of address: suppose mobile user moves to another 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 s transparent: on going connections can be maintained! Network Layer 4-4 Network Layer 4-4 Mobility via Direct Routing home correspondent requests, receives foreign address of mobile correspondent forwards to foreign agent wide area foreign agent receives packets, forwards to mobile visited mobile replies directly to 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 s? Network Layer 4-43 Network Layer

25 Mobile IP RF 30 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 Network Layer 4-45 Mobile IP: agent discovery agent advertisement: foreign/home agents advertise service by broadcasting IMP messages (typefield = 9) H,F bits: home and/or foreign agent R bit: registration required type = 9 code = 0 checksum router address type = 6 length sequence # RHFMGV registration lifetime reserved bits 0 or more care-ofaddresses standard IMP fields mobility agent advertisement extension Network Layer 4-46 Mobile IP: registration example visited : /4 home agent foreign agent H: O: IMP agent adv. Mobile agent O: M: registration req. registration req. O: O: H: H: M: M: Lifetime: 9999 Lifetime: 9999 identification:74 identification: 74. encapsulation format. registration reply time H: registration reply M: Lifetime: 4999 H: Identification: 74 M: encapsulation format Lifetime: Identification: 74. Network Layer 4-47 Network Layer: summary What we ve covered: layer services routing principles: link state and distance vector hierarchical routing IP Internet routing protocols RIP, OSPF, GP what s inside a router? IPv6 mobility Next stop: the Data link layer! Network Layer