1

Two issues in practice– Scale– Administrative autonomy

Autonomous system (AS) or region Intra autonomous system routing protocol Gateway routers Inter-autonoumous system routing protocol

Hierarchical routing

2

Fig 4.11

3

Fig 4.13

IPv4, IP version 6 Internet Control Message Protocol (ICMP)

The Internet Protocol (IP)

4

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

5

Fig 4.15

6

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

7

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

8

9

Fig 4.21

Addressing, Routing, and Forwarding

10

Fig 4.22

11

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.

IPv4 datagram format

12

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 reass

embly in the end systems rather than in network routers.

IP datagram fragmentation

13

Fig 4.24

14

Table 4.3

15

Error reporting Above IP Fig 4.25

ICMP

16

For a newly arriving host, the DHCP does– DHCP server discovery: broadcasting– DHCP server offer(s): the proposed IP address for the client, the ne

twork mask, and an IP address lease time– DHCP request– DHCP ACK

From a mobility aspect, how about DHCP?

DHCP

17

Fig 4.27

18

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

Network Address Translators (NATs)

19

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 uni

cast and multicast routing, and support for hierarchy within a single routing domain.

Routing in the Internet

20

Fig 4.35

21

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

22

Fig 4.38 (router arch)

Fig 4.39 (input port)

Router

23

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

Fig 4.40 (switching fabric)

25

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.

26

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.

27

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

28

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

IPv6 vs IPv4– Fragmentation/reassembly: IPv6 does not allow for fragmentation

and reassembly at intermediate routers.– Header checksum: IPv4 header checksum needed to be recompute

d at every router.– Options: next headers pointer in IPv6

ICMP for 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

30

Fig 4.45

Fig 4.46

31

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

– One-to-all unicast– Application-level multicast– Explicit multicast at the network layer

How to identify the receivers of a multicast datagram?– Address indirection: a single identifier is used for the group of rec

eivers -> class D and how to address a datagram sent to these receivers?

Multicast routing

32

Fig 4.47

33

Fig 4.48

34

IGMP– Group membership protocol– Locally between a host and an attached router– Means for a host to inform its attached router that an application ru

nning one the host wants to join a specific multicast group– Joining a multicast group is receiver-driven

Network-layer multicast algorithms (PIM, DVMRP, MOSPF)– Coordinate the multicast routers so that multicast datagrams are r

outed to their final destinations Table 4.4

35

Fig 4.50