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1、1,Chap 3,Switching need not be complete A timeout is associated with each entry.,9,Spanning Tree Algorithm,Problem: loops,10,HOMEWORK,Exercises 1，3，5，13，15，17 Required Reading Stallings chapter 3.1-3.2,11,Chap 4,IP (include subnet & CIDR) ARP ICMP IPv6,12,Connectionless (datagram-based) Best-effort
2、delivery (unreliable service) packets are lost packets are delivered out of order duplicate copies of a packet are delivered packets can be delayed for a long time Datagram format,Chap 4,13,Fragmentation & Reassembly,14,Global Addresses,Properties globally unique hierarchical: network + host,15,Subn
3、etting,Add another level to address/routing hierarchy: subnet Subnet masks define variable partition of host part Subnets visible only within site,16,Subnet Example,Forwarding table at router R1 Subnet Number Subnet Mask Next Hop 128.96.34.0 255.255.255.128 interface 0 128.96.34.128 255.255.255.128
4、interface 1 128.96.33.0 255.255.255.0 R2,Forwarding table at router R2 Subnet Number Subnet Mask Next Hop 128.96.34.0 255.255.255.128 R1 128.96.34.128 255.255.255.128 interface 0 128.96.33.0 255.255.255.0 interface 1,0,0,1,1,17,CIDR,Use subnetting to share one address among multiple physical network
5、s. CIDR collapses the multiple addresses onto one address Such as the class C network number from 192.4.16-192.4.31 has the same top 20 bits. IP forwarding revisited: The “longest match” princeple Such as the dest. IP =171.69.10.5 & 2 match network number (171.69 & 171.69.10),18,Chap 4,IP ARP ICMP I
6、Pv6,19,ARP table of IP to physical address bindings broadcast request if IP address not in table target machine responds with its physical address table entries are discarded if not refreshed (about 10 minutes) update table with source when you are the target,20,2,1,4,6,5,1. A checks the ARP cache 2
7、. A broadcasts ARP request 3. C adds As information into ARP cache 4. C responds ARP request 5. A adds Cs information into ARP cache 6. A sends IP packet,3,B,C,A,Address Translation,21,Chap 4,IP ARP ICMP IPv6,22,Internet Control Message Protocol,ICMP When a router receives an IP packet and finds err
8、ors, what should it do? Used by the routers to report errors and unexpected events, test the state of the network, perform congestion control, and router updates. The Internet is closely monitored by the routers using ICMP.,23,Chap 4,IP ARP ICMP IPv6,24,Problems with IPv4,Address depletion 232=4.3 b
9、illion addresses Most organizations apply for class B network. Does not support host mobility Not secure enough,25,IPv6,Permit the old and new protocols to coexist for years What IPv6 has: IPv6 addresses are 16 bytes long, instead of 4 bytes in IPv4. Provides an effectively unlimited supply of Inter
10、net addresses IPv6 header contains only 7 fields (versus 13 in IPv4) Allows faster process of packets IPv6 has better support for options. IPv6 improves security (authentication and privacy). IPv6 pays more attention to type of service.,26,IPv6 Addresses,Notation 47CD:1234:4422:AC02:0022:1234:A456:0
11、124 47CD:0000:0000:0000:0000:0000:A456:0124 47CD:A456:0124 :FFFF:128.96.33.81,27,IPv6 Addresses (cont.),Three types of IPv6 address (Table 4.11) Unicast address Multicast address Others (Anycast address),28,IPv6 Packet Headers,29,IPv6 Extension Headers,IPv6 implements several extension headers to al
12、low more options. Destination options - provides information for the destination Fragmentation header - provides information in the event that packet fragments must be reassembled. Hop-by-hop header - provides information that each router must examine Routing header - provides additional routing inf
13、ormation Security header - indicates the packets payload has been encrypted Authentication header - for IP authentication,30,Compatibility with IPv4, IPv4 will be around for a long time. IPv6 allows IPv4 addresses. What happens when an IPv6 packet has to pass through a IPv4 router? Tunnelling,31,Com
14、patibility with IPv4 (cont.), How to handle C having an IPv6 address?,32,HOMEWORK,Exercises 4，21，45，58 Review question 1. What is the Time to Live field in an IP packet? 2. How does IPv4 fragmentation differ from IPv6 fragmentation? Required Reading Stallings chapter 4.1, 4.3.1, 4.3.5,33,Chap 5,Simp
15、le Demultiplexer (UDP) Reliable Byte-Stream (TCP) Connection Establishment/Termination Sliding Window Revisited Flow Control,34,UDP,Transport protocol above IP Adds multiplexing by ports simply passes IP through to the upper (application) layers No flow control, No congestion control, No connection
16、Unreliable and unordered datagram service Gives apps the option to send packets unreliably Useful for multicast apps Minimal connection setup time : “connectionless” Low delay transmission for interactive text/audio/video Build own application-level protocol on top of UDP,35,UDP,UDP Header: Only 8 b
17、ytes! (vs. IP 20 bytes header) Source port for UDP sending process Dest port for UDP receiving process Length in bytes of UDP header + payload Checksum over UDP header + payload,Source Port #,Dest. Port #,UDP length,Checksum,16,32,UDP payload data,UDP payload,IP hdr,UDP hdr,36,TCP,Connection-oriente
18、d Reliable delivery of packets, in-order delivery Full duplex Flow control, Congestion control, Connection management,37,TCP Segment,A segment consists of a fixed 20-byte header (plus an optional part) followed by zero or more data bytes,Protection Against Wrap,Keeping the Pipe Full,38,Connection Es
19、tablishment,Active participant,(client),Passive participant,(server),SYN, SequenceNum =,x,SYN + ACK, SequenceNum =,y,ACK, Acknowledgment =,y,+,1,Acknowledgment =,x,+,1,SequenceNum =x+1,39,Connection Termination,40,State Transition Diagram,41,Flow Control (cont.) - Example,Assume each entity agree to
20、 a credit of 200 bytes Assume entities send 100 bytes in each TPDU,42,HOMEWORK,Exercises 10 Review question 1. How does TCP establish a connection? 2. Give the UDP segment format. Required Reading Stallings chapter 5.1, 5.2,43,Chap 9,Electronic Mail (SMTP) World Wide Web (HTTP) Name Service (DNS) Network Management (SNMP),