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Transcript
Hierarchical routing Two issues in practice – – Scale Administrative autonomy Autonomous system (AS) or region Intra autonomous system routing protocol Gateway routers Inter-autonoumous system routing protocol 1 Fig 4.11 2 The Internet Protocol (IP) Fig 4.13 IPv4, IP version 6 Internet Control Message Protocol (ICMP) 3 IPv4 addressing – – – – – An IP address is associated with an interface rather than with the host or router containing the interface. 32 bits long Dotted-decimal notation (pp. 322) Fig 4.14 223.1.1.0/24 where /24 -> a network mask, network prefix, an IP network, a network 4 Fig 4.15 5 Classful addressing: A, B, C, D Fig 4.17 Classless Interdomain Routing (CIDR): e.g., a.b.c.d/21 for 2000 hosts Corporation for Assigned Names and Numbers (ICANN) – – – – Allocate IP address Manage the DNS root servers Assign domain names Resolve domain name disputes 6 Obtaining a host address – – Manual configuration Dynamic Host Configuration Protocol (DHCP) 7 8 Addressing, Routing, and Forwarding Fig 4.21 9 Fig 4.22 10 IPv4 datagram format Fig 4.23 Type of service: differentiated service (e.g., Cisco) IPv6: no fragmentation at routers Why does TCP/IP perform error checking at the both layers? IP options were dropped in the IPv6 header. 11 IP datagram fragmentation MTU(max transfer unit): max amount of data that a link-layer packet can carry, e.g., 1,500 bytes for Ethernet, 576 bytes for wide-area links Fragment The designers of IPv4 decided to put the job of datagram reassembly in the end systems rather than in network routers. 12 Fig 4.24 13 Table 4.3 14 ICMP Error reporting Above IP Fig 4.25 15 DHCP For a newly arriving host, the DHCP does – – – – DHCP server discovery: broadcasting DHCP server offer(s): the proposed IP address for the client, the network mask, and an IP address lease time DHCP request DHCP ACK From a mobility aspect, how about DHCP? 16 Fig 4.27 17 Network Address Translators (NATs) The NAT-enabled router does not run an Inter-AS routing protocol. The NAT-enabled router behaves to the outside world as a single device with a single IP address. (port numbers) Fig 4.28 18 Routing in the Internet Intra-AS routing: RIP and OSPF Routing Information Protocol – – – – Distance vector protocol Hop count as a cost metric Max cost of a path: 15 Every 30 seconds for RIP advertisements Open Shortest Path First – – – Link state protocol Once every 30 minutes Adv.: security, multiple same-cost paths, integrated support for unicast and multicast routing, and support for hierarchy within a single routing domain. 19 Fig 4.35 20 Inter-AS routing: BGP – – – – Path vector protocol Exchange path information than cost information Routing policy On TCP 21 Router Fig 4.38 (router arch) Fig 4.39 (input port) 22 Given the need to operate at today’s high link speeds, a number of ways to find out an appropriate forwarding table entry. – – – – A linear search Store the forwarding table entries in a tree data structure Content addressable memories Forwarding table entries in a cache 23 Fig 4.40 (switching fabric) 24 Fig 4.41 (output ports) Packet queues at both the input ports and the output ports -> packet loss depending on the traffic load, the relative speed of the switching fabric, and the line speed. 25 Fig 4.42 Packet scheduler: choose one packet among queued for transmission – – – First-come-first-served (FCFS) scheduling Weighted fair queueing (WFQ) Important for quality-of-service guarantees. 26 Drop a packet before the buffer is full in order to provide a congestion signal to the sender -> active queue management (Random Early Detection (RED)) Head-of-the-line (HOL) blocking in an input-queued switch Fig 4.43 27 IPv6 Changes in IPv6 – – – – Expanded addressing capabilities (32 to 128 bits), anycast address A streamlined 40-byte header Flow labeling and priority Fig 4.44 28 IPv6 vs IPv4 – – – ICMP for IPv6 – – Fragmentation/reassembly: IPv6 does not allow for fragmentation and reassembly at intermediate routers. Header checksum: IPv4 header checksum needed to be recomputed at every router. Options: next headers pointer in IPv6 Packet too big, unrecognized IPv6 options error codes IGMP Transitioning from IPv4 to IPv6 – – – Flag day Dual-stack: DNS to determine whether another node is IPv6 or IPv4 Tunneling 29 Fig 4.45 Fig 4.46 30 Multicast routing Unicast vs multicast The sending of a packet from one sender to multiple receivers with a single send operation. Network-layer aspects of multicast Handle multicast groups – – – How to identify the receivers of a multicast datagram? – One-to-all unicast Application-level multicast Explicit multicast at the network layer Address indirection: a single identifier is used for the group of receivers -> class D How to address a datagram sent to these receivers? 31 Fig 4.47 32 Fig 4.48 33 IGMP – – – – Network-layer multicast algorithms (PIM, DVMRP, MOSPF) – Group membership protocol Locally between a host and an attached router Means for a host to inform its attached router that an application running one the host wants to join a specific multicast group Joining a multicast group is receiver-driven Coordinate the multicast routers so that multicast datagrams are routed to their final destinations Table 4.4 34 Fig 4.50 35 Fig 4.51 36 Multicast routing: the general case The goal of multicast routing is to find a tree of links that connects all of the routers that have attached hosts belonging to the multicast group. Fig 4.52 37 Two approaches: whether a single “group-shared” tree is used to distribute the traffic for all senders in the group, or whether a source-specific routing tree is constructed for each individual sender. Fig 4.53 38 Multicast routing using a group-shared tree – Fig 4.54 – Steiner tree problem: None of the existing Internet multicast routing algs has been based on this approach: information about all links is needed, rerun whenever link costs change and performance. Center-based approach: center node, rendezvous point or core: how to select the center – 39 Multicast routing using a source-based tree – – – Reverse path forwarding (RPF) Fig 4.56 If there were thousands of routers downstream from D, … -> pruning 40 Multicast routing in the Internet DVMRP: Distance Vector Multicast Routing Protocol – – – Source-based trees with reverse path forwarding and pruning Small fraction of the Internet routers are multicast-capable > Tunneling, e.g., Mbone Fig 4.57 41 Multicast routing in the Internet PIM: Protocol Independent Multicast – – – – Dense mode: a flood-and-prune reverse path forwarding Sparse mode: a center-based approach The ability to switch from a group-shared tree to a sourcespecific tree after joining the rendezvous point. UUNet Multicast Open Shortest Path First (MOSPF) DVMRP has been the de facto inter-AS multicast routing protocol 42 Mobility and the Network layer An Internet application needs to know the IP address and port number of the remote entity with which it is communicating. Fig 4.58 Ad hoc networking 43 Figure 4.59 44 Indirect routing to a mobile node – – – Triangle routing problem Encapsulation/decapsulation = tunneling Fig 4.60 45 – Fig 4.61 – The occasional datagram loss within a connection when a node moves between networks. 46 Direct routing to a mobile node – Fig 4.62 – GSM 47 Mobile IP Agent discovery, registration with the home agent, and indirect routing of datagram Security: authentication An agent receiving the solicitation will unicast an agent advertisement directly to the mobile node. Fig 4.63 48 – Fig 4.64 49