Computer Networking — A Top-down Approach Chpt 4
CHAPTER 4
1. Forwarding & Routing — difference; forwarding table
2. communication setup — require the routers along the chosen path from source to destination to handshake
3. Network Service Models — Constant bit rate (CBR) ATM network service; Available bit rate (ABR) ATM network service
4. virtual circuits (VCs)
Computer networks that provide only a connection service at the network layer are called virtual-circuit (VC) networks
computer networks that provide only a connectionless service at the network layer are called datagram networks
5. VC setup
routers along the path between the two end systems are involved in VC setup, and each router is fully aware of all the VCs passing through it.
6. Datagram Networks — VC network is arguably more complex than a datagram network
7. Router
Input ports; Switching fabric; Output ports; Routing processor
8. Input port processing — termination function →link-layer processing →lookup, forwarding queue →switch fabric
9. Switch — Heart of a router; switch is forwarding; via memory; via a bus; via interconnection network
10. Output processing — packets may lost during queue; buffer size should be very large to suit the queuing
11. Packet scheduling plays a crucial role in providing quality-of-service guarantees
12. Random Early Detection (RED) algorithm — when buffer full
13. head-of-the-line (HOL) blocking will happen
14. IP: forwarding and addressing in the internet
15. Network-layer packet is referred to as a datagram
16. Raison d’être — reason for existence
17. The maximum amount of data that a link-layer frame can carry is called the maximum transmission unit (MTU)
18. if IP datagram > MTU → fragment the data into smaller IP datagrams
19. an IP address is technically associated with an interface, rather than with the host or router containing that interface.
20. 192.168.10.10 is a dotted-decimal notation
21. 223.1.1.0/24; /24 is a subnet mask
22. The Internet’s address assignment strategy is known as Classless Interdomain Routing (CIDR — pronounced cider)
23. use longest prefix matching to route toward small subnet
24. 255.255.255.255 broadcast address
25. ISP & its customers’ subnet
26. Obtaining a Host Address: the Dynamic Host Configuration Protocol
27. DHCP server discovery use DHCP discover message — destination broadcast IP address, source IP; DHCP server offers — may get several; DHCP request; DHCP ACK
28. Network Address Translation (NAT) — NAT translation table is to know the internal host； NAT router will change IP address & port number for source
29. Peer behind NAT cannot directly contact another peer; connection reversal is needed; NAT traversal
30. UPnP — Universal Plug and Play; ask NAT to create a hole that map (private IP, port) → (public IP, port)
31. Internet Control Message Protocol (ICMP)
32. network layer of the internet has 3 main components: IP protocol; internet routing protocol; ICMP
33. ICMP lies architecturally above IP — ICMP msg is inside of IP datagrams; first 8 bytes of the IP datagram that caused error; Traceroute is implemented with ICMP messages;
34. use traceroute [-T][-I]; mtr google.com.sg --report; tracepath
35. IP v6
every grain of sand on the planet can be IP-addressable;
anycast address — deliver datagrams to any one of a group hosts;
40-byte header;
Flow labeling and priority — it is a foresee; 20-bit;
36. Transitioning from IPv4 to IPv6 — IPv6-capable systems can be made backward-capable; dual-stack approach;
37. tunneling — IPv4 encapsulating IPv6
38. IP Security — IPsec is connection-oriented;
39. Routing Algorithms
40. goal: find a shortest path
41. Link-State (LS) Routing Algorithm — Dijkstra’s algorithm
42. The Distance-Vector (DV) Routing Algorithm — bellman-ford algorithm; decentralized
DV-like algorithms are used in many routing protocols in practice, including the Internet’s RIP and BGP, ISO IDRP, Novell IPX, and the original ARPAnet.
43. Routing loop can happen when y think z is shorter way, z think y is shorter way
44. use poisoned reverse to lie
45. Hierarchical Routing — Scale; Administrative autonomy; Autonomous System; add gateway routers to response outside
46. inter-SA & intra-SA
47. Routing the Internet
An intra-AS routing protocol is used to determine how routing is performed within an autonomous system (AS). Intra-AS routing protocols are also known as interior gateway protocols
48. Intra-AS Routing Information Protocol — RIP uses the term hop, which is the number of subnets traversed along the shortest path from source router to destination subnet, including the destination subnet; RIP response message/30sec;
49. Intra-AS Routing in the Internet: OSPF — OSPF is a link-state protocol that uses flooding of link-state information and a Dijkstra least-cost path algorithm; Can be configured hierarchically;
50. Inter-AS Routing: BGP — Border Gateway Protocol; TCP connection to send BGP msg is BGP session; external BGP (eBGP) session span 2 ASs; internal BGP (iBGP) session in the same AS;
51. //TODO BGP read again
52. Inter-AS vs Intra-AS — differences between the goals: Inter-AS Policy-oriented; Inter-AS for scale; Intra-AS focuses more on performances
53. de facto — the truth/fact
54. Broadcast and Multicast Routing
55. Broadcast Routing Algorithms — N-way-unicast: duplicated packets from source; Uncontrolled flooding; Controlled flooding — add source ip | if not shortest path to me, i will not send out; Spanning-Tree Broadcast — centre-based spanning tree;
56. Broadcast Algorithm in Practice
Broadcast protocols are used in practice at both the application and network layers.
57. Multicast — how to identify the receivers of a multicast packet; how to address a packet sent to these receivers
58. Internet Group Management Protocol — join/leave a multicast group
59. Multicast Routing in the Internet — Distance-vector Multicast Routing Protocol;
