1 o Two issues in practice – Scale – Administrative autonomy o Autonomous system (AS) or region o Intra autonomous system routing protocol o Gateway routers o Inter-autonoumous system routing protocol Hierarchical routing

2 o Fig 4.11

3 o Fig 4.13 o IPv4, IP version 6 o Internet Control Message Protocol (ICMP) The Internet Protocol (IP)

4 o 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 – /24 where /24 -> a network mask, network prefix, an IP network, a network

5 o Fig 4.15

6 o Classful addressing: A, B, C, D o Fig 4.17 o Classless Interdomain Routing (CIDR): e.g., a.b.c.d/21 for 2000 hosts o Corporation for Assigned Names and Numbers (ICANN) – Allocate IP address – Manage the DNS root servers – Assign domain names – Resolve domain name disputes

7 o Obtaining a host address – Manual configuration – Dynamic Host Configuration Protocol (DHCP)

8

9 o Fig 4.21 Addressing, Routing, and Forwarding

10 o Fig 4.22

11 o Fig 4.23 o Type of service: differentiated service (e.g., Cisco) o IPv6: no fragmentation at routers o Why does TCP/IP perform error checking at the both layers? o IP options were dropped in the IPv6 header. IPv4 datagram format

12 o 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 o Fragment o The designers of IPv4 decided to put the job of datagram reassembly in the end systems rather than in network routers. IP datagram fragmentation

13 o Fig 4.24

14 o Table 4.3

15 o Error reporting o Above IP o Fig 4.25 ICMP

16 o 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 o From a mobility aspect, how about DHCP? DHCP

17 o Fig 4.27

18 o The NAT-enabled router does not run an Inter-AS routing protocol. o The NAT-enabled router behaves to the outside world as a single device with a single IP address. (port numbers) o Fig 4.28 Network Address Translators (NATs)

19 o Intra-AS routing: RIP and OSPF o Routing Information Protocol – Distance vector protocol – Hop count as a cost metric – Max cost of a path: 15 – Every 30 seconds for RIP advertisements o 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. Routing in the Internet

20 o Fig 4.35

21 o Inter-AS routing: BGP – Path vector protocol – Exchange path information than cost information – Routing policy – On TCP

22 o Fig 4.38 (router arch) o Fig 4.39 (input port) Router

23 o 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

24 o Fig 4.40 (switching fabric)

25 o Fig 4.41 (output ports) o 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.

26 o Fig 4.42 o 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.

27 o 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)) o Head-of-the-line (HOL) blocking in an input-queued switch o Fig 4.43

28 o Changes in IPv6 – Expanded addressing capabilities (32 to 128 bits), anycast address – A streamlined 40-bute header – Flow labeling and priority – Fig 4.44 IPv6

29 o IPv6 vs IPv4 – 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 o ICMP for IPv6 – Packet too big, unrecognized IPv6 options error codes – IGMP o Transitioning from IPv4 to IPv6 – Flag day – Dual-stack: DNS to determine whether another node is IPv6 or IPv4 – Tunneling

30 o Fig 4.45 o Fig 4.46

31 o Unicast vs multicast o The sending of a packet from one sender to multiple receivers with a single send operation. o Network-layer aspects of multicast o Handle multicast groups – One-to-all unicast – Application-level multicast – Explicit multicast at the network layer o How to identify the receivers of a multicast datagram? – Address indirection: a single identifier is used for the group of receivers -> class D o and how to address a datagram sent to these receivers? Multicast routing

32 o Fig 4.47

33 o Fig 4.48

34 o IGMP – 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 o Network-layer multicast algorithms (PIM, DVMRP, MOSPF) – Coordinate the multicast routers so that multicast datagrams are routed to their final destinations o Table 4.4

35 o Fig 4.50