Network Layer Outline (PDF)

Network Layer: outline 4.1 introduction 4.5 routing algorithms 4.2 virtual circuit and § link state datagram networks § distance vector 4.3 what s inside a router § hierarchical routing 4.4 IP: Internet Protocol 4.6 routing in the Internet § datagram fo...

Network Layer: outline 4.1 introduction 4.5 routing algorithms 4.2 virtual circuit and § link state datagram networks § distance vector 4.3 what s inside a router § hierarchical routing 4.4 IP: Internet Protocol 4.6 routing in the Internet § datagram format § RIP § IPv4 addressing § OSPF § BGP § ICMP § IPv6 4.7 broadcast and multicast routing Network Layer 3 IP addressing: introduction 223.1.1.1 v IP address: 32-bit 223.1.2.1 identifier for host, router interface 223.1.1.2 223.1.1.4 223.1.2.9 v interface: connection between host/router and 223.1.3.27 physical link 223.1.1.3 223.1.2.2 § router s typically have multiple interfaces § host typically has one or 223.1.3.1 223.1.3.2 two interfaces (e.g., wired Ethernet, wireless 802.11) v IP addresses associated with each interface 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 Network Layer 4 IP addressing: introduction 223.1.1.1 Q: how are interfaces 223.1.2.1 actually connected? A: we’ll learn about that 223.1.1.2 223.1.1.4 223.1.2.9 in the link layer 223.1.3.27 223.1.1.3 223.1.2.2 A: wired Ethernet interfaces connected by Ethernet switches 223.1.3.1 223.1.3.2 For now: don’t need to worry about how one interface is connected to another (with no A: wireless WiFi interfaces intervening router) connected by WiFi base station Network Layer 5 Subnets v IP address: 223.1.1.1 § subnet part - high order bits 223.1.1.2 223.1.2.1 223.1.1.4 223.1.2.9 § host part - low order bits 223.1.2.2 223.1.1.3 223.1.3.27 v what s a subnet ? § device interfaces with subnet same subnet part of IP address 223.1.3.1 223.1.3.2 § can physically reach each other without intervening router network consisting of 3 subnets Network Layer 6 Subnets 223.1.1.0/24 223.1.2.0/24 recipe 223.1.1.1 v to determine the 223.1.1.2 223.1.2.1 subnets, detach each 223.1.1.4 223.1.2.9 interface from its host 223.1.2.2 or router, creating 223.1.1.3 223.1.3.27 islands of isolated subnet networks 223.1.3.2 v each isolated network 223.1.3.1 is called a subnet 223.1.3.0/24 subnet mask: /24 Network Layer 7 Subnets 223.1.1.2 how many? 223.1.1.1 223.1.1.4 223.1.1.3 223.1.9.2 223.1.7.0 223.1.9.1 223.1.7.1 223.1.8.1 223.1.8.0 223.1.2.6 223.1.3.27 223.1.2.1 223.1.2.2 223.1.3.1 223.1.3.2 Network Layer 8 Original Internet Addresses v First eight bits: network address (/8) v Last 24 bits: host address Assumed 256 networks were more than enough! Network Layer 9 Next Design: “Classful” Addressing v Three main classes 0 8 126 nets § Class A 0 network host ~16M hosts 0 16 ~16K nets 10 network host § Class B ~65K hosts 0 24 ~2M nets § Class C 1 10 network host 254 hosts Problem: Networks only come in three sizes! Network Layer 10  Today’s addressing: CIDR CIDR: Classless InterDomain Routing § subnet portion of address of arbitrary length § address format: a.b.c.d/x, where x is # bits in subnet portion of address 200.23.17.255 subnet host part part 11001000 00010111 00010000 00000000 /23 200.23.16.0/23 IP address 200.23.16.0 Network Layer 11  223.1.1.0/24 223.1.2.0/24 Subnet Address v Subnet Mask B: 223.1.1.2 § Used in conjunction to with the network address to indicate how many higher order bits are used for the network part of the address (i.e. network prefix) Bit-wise AND § 223.1.1.0/24 is equivalent to 223.1.1.0 with subnet mask 255.255.255.0 223.1.3.0/24 v Broadcast Address Host B Dot-decimal Binary § host part is all 111’s address § E.g. 223.1.1.255 IP address 223.1.1.2 11111101.00000001.00000001.00000010 Subnet Address Subnet Mask 255.255.255.0 11111111.11111111.11111111.00000000 v Network Part 223.1.1.0 11111101.00000001.00000001.00000000 § Host part is all 0000’s Host Part 0.0.0.2 00000000.00000000.00000000.00000010 § E.g. 223.1.1.0 Network Layer 12 v Both of these are not assigned IP addresses: how to get one? Q: How does a host get IP address? v hard-coded by system admin in a file § Windows: control-panel->network->configuration->tcp/ ip->properties § UNIX: /etc/rc.config v DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server § plug-and-play Network Layer 13 DHCP: Dynamic Host Configuration Protocol goal: allow host to dynamically obtain its IP address from network server when it joins network § can renew its lease on address in use § allows reuse of addresses (only hold address while connected/ on ) § support for mobile users who want to join network (more shortly) DHCP overview: § host broadcasts DHCP discover msg § DHCP server responds with DHCP offer msg § host requests IP address: DHCP request msg § DHCP server sends address: DHCP ack msg Network Layer 14 DHCP client-server scenario DHCP 223.1.1.0/24 server 223.1.1.1 223.1.2.1 223.1.1.2 arriving DHCP 223.1.1.4 223.1.2.9 client needs address in this 223.1.1.3 223.1.3.27 223.1.2.2 network 223.1.2.0/24 223.1.3.1 223.1.3.2 223.1.3.0/24 Network Layer 15 DHCP client-server scenario DHCP server: 223.1.2.5 DHCP discover arriving client src : 0.0.0.0, 68 dest.: 255.255.255.255,67 yiaddr: 0.0.0.0 transaction ID: 654 DHCP offer src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 654 lifetime: 3600 secs DHCP request src: 0.0.0.0, 68 dest:: 255.255.255.255, 67 yiaddrr: 223.1.2.4 transaction ID: 655 lifetime: 3600 secs DHCP ACK src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 655 lifetime: 3600 secs Network Layer 16 DHCP: more than IP addresses DHCP can return more than just allocated IP address on subnet: § address of first-hop router for client § name and IP address of DNS sever § network mask (indicating network versus host portion of address) Network Layer 17 DHCP: example DHCP DHCP v connecting laptop needs DHCP DHCP UDP its IP address, addr of DHCP IP first-hop router, addr of Eth DNS server: use DHCP Phy DHCP v DHCP request encapsulated in UDP, encapsulated in IP, DHCP DHCP 168.1.1.1 encapsulated in 802.1 DHCP UDP Ethernet DHCP IP v Ethernet frame broadcast DHCP Eth router with DHCP server built into (dest: FFFFFFFFFFFF) on LAN, Phy received at router running router DHCP server v Ethernet demuxed to IP demuxed, UDP demuxed to DHCP Network Layer 18 DHCP: example DHCP DHCP v DCP server formulates DHCP UDP DHCP ACK containing DHCP IP client s IP address, IP DHCP Eth address of first-hop Phy router for client, name & IP address of DNS server v encapsulation of DHCP DHCP DHCP server, frame forwarded DHCP UDP to client, demuxing up to DHCP IP DHCP at client DHCP Eth router with DHCP DHCP Phy server built into v client now knows its IP router address, name and IP address of DSN server, IP address of its first-hop router Network Layer 19  DHCP: Wireshark Message type: Boot Reply (2) reply output (home LAN) Hardware type: Ethernet Hardware address length: 6 Hops: 0 Transaction ID: 0x6b3a11b7 request Seconds elapsed: 0 Bootp flags: 0x0000 (Unicast) Message type: Boot Request (1) Client IP address: 192.168.1.101 (192.168.1.101) Hardware type: Ethernet Your (client) IP address: 0.0.0.0 (0.0.0.0) Hardware address length: 6 Next server IP address: 192.168.1.1 (192.168.1.1) Hops: 0 Relay agent IP address: 0.0.0.0 (0.0.0.0) Transaction ID: 0x6b3a11b7 Client MAC address: Wistron_23:68:8a (00:16:d3:23:68:8a) Seconds elapsed: 0 Server host name not given Bootp flags: 0x0000 (Unicast) Boot file name not given Client IP address: 0.0.0.0 (0.0.0.0) Magic cookie: (OK) Your (client) IP address: 0.0.0.0 (0.0.0.0) Option: (t=53,l=1) DHCP Message Type = DHCP ACK Next server IP address: 0.0.0.0 (0.0.0.0) Option: (t=54,l=4) Server Identifier = 192.168.1.1 Relay agent IP address: 0.0.0.0 (0.0.0.0) Option: (t=1,l=4) Subnet Mask = 255.255.255.0 Client MAC address: Wistron_23:68:8a (00:16:d3:23:68:8a) Option: (t=3,l=4) Router = 192.168.1.1 Server host name not given Option: (6) Domain Name Server Boot file name not given Length: 12; Value: 445747E2445749F244574092; Magic cookie: (OK) IP Address: 68.87.71.226; Option: (t=53,l=1) DHCP Message Type = DHCP Request IP Address: 68.87.73.242; Option: (61) Client identifier IP Address: 68.87.64.146 Length: 7; Value: 010016D323688A; Option: (t=15,l=20) Domain Name = "hsd1.ma.comcast.net." Hardware type: Ethernet Client MAC address: Wistron_23:68:8a (00:16:d3:23:68:8a) Option: (t=50,l=4) Requested IP Address = 192.168.1.101 Option: (t=12,l=5) Host Name = "nomad" Option: (55) Parameter Request List Length: 11; Value: 010F03062C2E2F1F21F92B 1 = Subnet Mask; 15 = Domain Name 3 = Router; 6 = Domain Name Server 44 = NetBIOS over TCP/IP Name Server …… Network Layer 20 DHCP: further details v DHCP uses UDP and port numbers 67 (server side) and 68 (client side) v Usually the MAC address is used to identify clients § DHCP server can be configured with a registered list of acceptable MAC addresses v DHCP offer message includes ip address, length of lease, subnet mask, DNS servers, default gateway v DHCP security holes § DoS attack by exhausting pool of IP addresses § Masquerading as a DHCP server § Authentication for DHCP - RFC 3118 Network Layer 21 IP addresses: how to get one? Q: how does network get subnet part of IP addr? A: gets allocated portion of its provider ISP s address space ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20 Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23 Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23... ….. …. …. Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23 Network Layer 22  CIDR: Addresses allocated in contiguous prefix chunks Recursively break down chunks as get closer to host 12.0.0.0/15 12.3.0.0/22 : 12.2.0.0/16 12.3.4.0/24 : 12.3.0.0/16 : : : 12.3.254.0/23 12.0.0.0/8 : : 12.253.0.0/19 12.253.32.0/19 12.253.64.0/19 12.253.0.0/16 12.253.64.108/30 : 12.253.96.0/18 12.253.128.0/17 Network Layer 23 Hierarchical addressing: route aggregation hierarchical addressing allows efficient advertisement of routing information: Organization 0 200.23.16.0/23 Organization 1 Send me anything 200.23.18.0/23 with addresses Organization 2 beginning 200.23.20.0/23. Fly-By-Night-ISP 200.23.16.0/20... Internet. Organization 7. 200.23.30.0/23 Send me anything ISPs-R-Us with addresses beginning 199.31.0.0/16 Network Layer 24  Quiz: What should we do if organization 1 decides to switch to ISPs-R-Us Organization 0 200.23.16.0/23 Organization 1 Send me anything 200.23.18.0/23 with addresses Organization 2 beginning 200.23.20.0/23. Fly-By-Night-ISP 200.23.16.0/20... Internet. Organization 7. 200.23.30.0/23 Send me anything ISPs-R-Us with addresses beginning 199.31.0.0/16 A: Move 200.23.18.0/23 to ISPs-R-Us (and break up Fly-By-Night’s/20 block). B: Give new addresses to Organization 1 (and force them to change all their addresses) C: Some other solution Network Layer 25 Hierarchical addressing: more specific routes ISPs-R-Us has a more specific route to Organization 1 Organization 0 Longest prefix matching 200.23.16.0/23 Send me anything with addresses Organization 2 beginning 200.23.20.0/23. Fly-By-Night-ISP 200.23.16.0/20... Internet. Organization 7. 200.23.30.0/23 Send me anything ISPs-R-Us with addresses Organization 1 beginning 199.31.0.0/16 or 200.23.18.0/23 200.23.18.0/23 Network Layer 26 Example: continued v But how will this work? v Routers in the Internet will have two entries in their tables 200.23.31.255 § 200.23.16.0/20 (Fly-by-Night-ISP) /20 § 200.23.18.0/23 (ISPs-R-Us) 200.23.19.255 v Longest prefix match /23 200.23.18.0 200.23.16.0 IP address White Paper on IP addresses linked to page - Very informative Network Layer 27  More on IP addresses Source: www.xkcd.com v IP addresses are allocated as blocks and have geographical significance v It is possible to determine the geographical location of an IP address http://www.geobytes.com/IpLocator.htm Network Layer 28 IP addressing: the last word... Q: how does an ISP get block of addresses? A: ICANN: Internet Corporation for Assigned Names and Numbers http://www.icann.org/ § allocates addresses § manages DNS § assigns domain names, resolves disputes v Regional Internet Registries (RIR) act as intermediaries § RIPE NCC (Riseaux IP Europiens Network Coordination Center) for Europe, Middle East, Africa § APNIC (Asia Pacific Network Information Center) for Asia and Pacific § ARIN (American Registry for Interent Numbers) for the Americas, Caribbean, sub-Saharan Africa § LACNIC (Latin America and Caribbean) Network Layer 29 Made-up Example in More Detail v ICANN gives APNIC several /8s v APNIC gives Telstra one /8, 129.0/8 § Network Prefix: 10000001 v Telstra gives UNSW a /16, 129.94/16 § Network Prefix: 1000000101011110 v UNSW gives CSE a /24, 12.197.242/24 § Network Prefix: 100000010101111011110010 v CSE gives me a specific address 129.94.242.51 § Address: 10000001010111101111001000110011 Network Layer 30 Quiz: Header Fields v Which of the following fields is not part of either a TCP or UDP header? A. Source port B. Source IP address C. Receive window D. Length E. Checksum Network Layer 31 Quiz: DHCP v What transport protocol does DHCP use? A. UDP B. TCP C. IP D. HTTP Network Layer 32  Quiz: IP Addressing v How many IP addresses belong to the subnet 128.119.254.0/25 ? What are the IP addresses at the two end-points of this range ? Answer: 27 = 128 addresses (126 are usable) 128.119.254.127 subnet host part part 10000000 01110111 11111110 00000000 /25 128.119.254.0/25 IP address 128.119.254.0 Network Layer 33 Quiz: Subnets v How many subnets are there in this network? 223.1.8.1 223.1.8.0 223.1.2.6 223.1.3.27 223.1.2.1 223.1.2.2 223.1.3.1 223.1.3.2 Network Layer 34  Quiz: Subnets v The two subnets 128.119.245.129/25 and 128.119.245.4/26 have overlapping IP addresses. A. True B. False subnet host part part 10000000 01110111 11111110 10000001 128.119.254.129/25 subnet host part part 10000000 01110111 11111110 00000100 128.119.254.4/26 Network Layer 35 Network Layer 4-36 Private Addresses v Defined in RFC 1918: - 10.0.0./8 (16,777,216 hosts) - 172.16.0.0/12 (1,048,576 hosts) - 192.168.0.0/16 (65536 hosts) v These addresses cannot be routed - Anyone can use them - Often used for NAT Network Layer 37  NAT: network address translation rest of local network Internet (e.g., home network) 10.0.0/24 10.0.0.1 10.0.0.4 10.0.0.2 138.76.29.7 10.0.0.3 all datagrams leaving local datagrams with source or network have same single destination in this network source NAT IP address: have 10.0.0/24 address for 138.76.29.7,different source source, destination (as usual) port numbers Network Layer 38 NAT: network address translation implementation: NAT router must: § outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #)... remote clients/servers will respond using (NAT IP address, new port #) as destination addr § remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair § incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table Network Layer 39  NAT: network address translation NAT translation table 2: NAT router 1: host 10.0.0.1 WAN side addr LAN side addr sends datagram to changes datagram source addr from 138.76.29.7, 5001 10.0.0.1, 3345 128.119.40.186, 80 10.0.0.1, 3345 to …… …… 138.76.29.7, 5001, updates table S: 10.0.0.1, 3345 D: 128.119.40.186, 80 10.0.0.1 1 S: 138.76.29.7, 5001 2 D: 128.119.40.186, 80 10.0.0.4 10.0.0.2 138.76.29.7 S: 128.119.40.186, 80 D: 10.0.0.1, 3345 4 S: 128.119.40.186, 80 D: 138.76.29.7, 5001 3 10.0.0.3 4: NAT router 3: reply arrives changes datagram dest. address: dest addr from 138.76.29.7, 5001 138.76.29.7, 5001 to 10.0.0.1, 3345 Network Layer 40  NAT Advantages Local network uses just one IP address as far as outside world is concerned: § range of addresses not needed from ISP: just one IP address for all devices § can change addresses of devices in local network without notifying outside world § can change ISP without changing addresses of devices in local network Network Layer 41 Quiz: NAT v Devices inside the local network are not explicitly addressable or visible by outside world. A: This is an advantage B: This is a disadvantage Network Layer 42 NAT: network address translation v 16-bit port-number field: § 60,000 simultaneous connections with a single LAN-side address! v NAT is controversial: § routers should only process up to layer 3 § violates end-to-end argument NAT possibility must be taken into account by app designers, e.g., P2P applications § address shortage should instead be solved by IPv6 Network Layer 43 NAT: Practical Issues v NAT modifies port # and IP address § Requires recalculation of TCP and IP checksum v Some applications embed IP address or port numbers in their message payloads § DNS, FTP (PORT command), SIP, H.323 § For legacy protocols, NAT must look into these packets and translate the embedded IP addresses/port numbers § Duh, What if these fields are encrypted ?? (SSL/TLS, IPSEC, etc) § Q: In some cases why may NAT need to change TCP sequence number?? v If applications change port numbers periodically, the NAT must be aware of this v NAT Traversal Problems § E.g: How to setup a server behind a NAT router? § How to talk to a Skype user behind a NAT router? § Possible workarounds in next few slides Network Layer 44 NAT traversal problem v client wants to connect to server with address 10.0.0.1 § server address 10.0.0.1 local to 10.0.0.1 client LAN (client can t use it as destination addr) ? § only one externally visible NATed 10.0.0.4 address: 138.76.29.7 v solution1: statically configure 138.76.29.7 NAT NAT to forward incoming router connection requests at given port to server § e.g., (123.76.29.7, port 2500) always forwarded to 10.0.0.1 port 25000 Network Layer 45 NAT traversal problem v solution 2: Universal Plug and Play (UPnP) Internet Gateway Device (IGD) Protocol. Allows NATed 10.0.0.1 host to: IGD v learn public IP address (138.76.29.7) v add/remove port mappings (with lease times) NAT router i.e., automate static NAT port map configuration Network Layer 46  NAT traversal problem v solution 3: relaying (used in Skype) § NATed client establishes connection to relay § external client connects to relay § relay bridges packets between to connections 2. connection to relay initiated 1. connection to 10.0.0.1 by client relay initiated by NATed host 3. relaying client established 138.76.29.7 NAT router Network Layer 47 NAT: Devil in the details v Despite the problems, NAT has been widely deployed v Most protocols can be successfully passed through a NAT, including VPN v Modern hardware can easily perform NAT functions at > 100 Mbps v IPv6 is still not widely deployed commercially, so the need for NAT is real v After years of refusing to work on NAT, the IETF has been developing “NAT control protocols” for hosts v Lot of practical variations § Full-cone NAT, Restricted Cone NAT, Port Restricted Cone NAT, Symmetric NAT, ….. The devil is in the detail v External link under lecture notes for further reading (not examinable) Network Layer 48 Network Layer: outline 4.1 introduction 4.5 routing algorithms 4.2 virtual circuit and § link state datagram networks § distance vector 4.3 what s inside a router § hierarchical routing 4.4 IP: Internet Protocol 4.6 routing in the Internet § datagram format § RIP § IPv4 addressing § OSPF § BGP § ICMP § IPv6 4.7 broadcast and multicast routing Network Layer 49 ICMP: internet control message protocol v used by hosts & routers Type Code description to communicate network- 0 0 echo reply (ping) level information 3 0 dest. network unreachable § error reporting: 3 1 dest host unreachable unreachable host, network, 3 2 dest protocol unreachable port, protocol 3 3 dest port unreachable § echo request/reply (used by 3 6 dest network unknown ping) 3 7 dest host unknown v network-layer above IP: 4 0 source quench (congestion § ICMP msgs carried in IP control - not used) datagrams 8 0 echo request (ping) 9 0 route advertisement v ICMP message: type, code 10 0 router discovery plus first 8 bytes of IP 11 0 TTL expired datagram causing error 12 0 bad IP header Network Layer 50 Traceroute and ICMP v source sends series of v when ICMP messages UDP segments to dest arrives, source records § first set has TTL =1 RTTs § second set has TTL=2, etc. § unlikely port number stopping criteria: v when nth set of datagrams v UDP segment eventually arrives to nth router: arrives at destination host § router discards datagrams v destination returns ICMP § and sends source ICMP port unreachable messages (type 11, code 0) message (type 3, code 3) § ICMP messages includes v source stops name of router & IP address 3 probes 3 probes 3 probes Network Layer 51  IPv6: motivation v initial motivation: 32-bit address space soon to be completely allocated. v additional motivation: § header format helps speed processing/forwarding § header changes to facilitate QoS IPv6 datagram format: § fixed-length 40 byte header § no fragmentation allowed https://www.google.com/intl/en/ipv6/statistics.html Network Layer 52  IPv6 datagram format priority: identify priority among datagrams in flow (traffic class) flow Label: identify datagrams in same flow. (concept of flow not well defined). next header: identify upper layer protocol for data ver pri flow label payload len next hdr hop limit source address (128 bits) destination address (128 bits) data 32 bits Network Layer 53 Other changes from IPv4 v checksum: removed entirely to reduce processing time at each hop v options: allowed, but outside of header, indicated by Next Header field v ICMPv6: new version of ICMP § additional message types, e.g. Packet Too Big § multicast group management functions Network Layer 54 Transition from IPv4 to IPv6 v not all routers can be upgraded simultaneously § no flag days § how will network operate with mixed IPv4 and IPv6 routers? v tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers IPv4 header fields IPv6 header fields IPv4 payload IPv4 source, dest addr IPv6 source dest addr UDP/TCP payload IPv6 datagram IPv4 datagram Network Layer 55 Tunneling A B IPv4 tunnel E F connecting IPv6 routers logical view: IPv6 IPv6 IPv6 IPv6 A B C D E F physical view: IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 Network Layer 56 Tunneling A B IPv4 tunnel E F connecting IPv6 routers logical view: IPv6 IPv6 IPv6 IPv6 A B C D E F physical view: IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 flow: X src:B src:B flow: X src: A dest: E src: A dest: F dest: E dest: F Flow: X Flow: X Src: A Src: A data Dest: F Dest: F data data data A-to-B: E-to-F: IPv6 B-to-C: B-to-C: IPv6 IPv6 inside IPv6 inside IPv4 IPv4 Network Layer 57 Quiz: NAT v A host with a private IP address 192.168.0.2 opens a TCP socket on its local port 4567 and connects to a web server at 34.5.6.7. The NAT’s public IP address is 22.33.44.55. Which of the following mapping entries could the NAT create as a result? 22.33.44.55 192.168.0.2 A. [22.33.44.55, 3333]à[192.168.0.2, 80] NAT B. [34.5.6.7, 80] à [22.33.44.55, 4567] router C. [192.168.0.2, 80]à[34.5.6.7, 4567] D. [22.33.44.55, 3967]à[192.168.0.2, 4567] 34.5.6.7 Network Layer 58 Quiz: NAT v A host with a private IP address 192.168.0.2 opens a TCP socket on its local port 4567 and connects to a web server at 34.5.6.7. The NAT’s public IP address is 22.33.44.55. Suppose the NAT created the mapping [22.33.44.55, 3967]à[192.168.0.2, 4567] as a result. What are the source and destination port numbers in the SYNACK response from the server? 22.33.44.55 192.168.0.2 A. 80, 3967 NAT B. 4567, 80 router C. 3967, 80 D. 3967, 4567 34.5.6.7 Network Layer 59 Quiz: IPv6 v Which of the following is not true? A. IPv6 increases the size of the IP address space from 2^32 to 2^128. B. IPv6 removes checksums and fragmentation compared to IPv4. C. IPv6 has fixed length headers. D. IPv6 adds reliability at the network layer. Network Layer 60