Addressing 1 Outline Network addressing q Network packet

Addressing 1

Outline Ø Network addressing q Network packet format and forwarding q NAT, DHCP, IPv 6 2

IP Addressing: introduction q IP address: 32 -bit identifier for host, router interface q interface: connection between host/router and physical link m router’s typically have multiple interfaces m host may have multiple interfaces m IP addresses associated with each interface 223. 1. 1. 1 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 1 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 223. 1. 1. 1 = 11011111 00000001 223 1 1 1 3

IP Addressing q IP address: m network part (high order bits) m host part (low order bits) q What’s a network ? (from IP address perspective) m device interfaces with same network part of IP address m can physically reach other without intervening router 223. 1. 1. 1 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 1 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 LAN 223. 1. 3. 2 network consisting of 3 IP networks (for IP addresses starting with 223, first 24 bits are network address) 4

IP Addressing How to find the networks? q Detach each interface from router, host q create “islands of isolated networks 223. 1. 1. 2 223. 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 How many isolated networks? Interconnected system consisting of six networks 223. 1. 2. 1 223. 1. 8. 0 223. 1. 2. 6 223. 1. 3. 27 223. 1. 2. 2 223. 1. 3. 2 5

IP address classes 8 16 Class A 0 Network ID 24 32 Host ID 1. 0. 0. 0 to 127. 255 Class B 10 Network ID Host ID 128. 0. 0. 0 to 191. 255 Class C 110 Network ID Host ID 192. 0. 0. 0 to 223. 255 Class D 1110 Multicast Addresses 224. 0. 0. 0 to 239. 255 Class E 1111 Reserved for experiments 6

Special IP Addresses q 127. *. *. *: local host (a. k. a. the loopback address) q Private addresses m http: //www. rfc-editor. org/rfc 1918. txt m Class A: 10. 0 - 10. 255 (10/8 prefix) m Class B: 172. 16. 0. 0 - 172. 31. 255 (172. 16/12 prefix) m Class C: 192. 168. 0. 0 - 192. 168. 255 (192. 168/16 prefix) q 255 m IP broadcast to local hardware that must not be forwarded m http: //www. rfc-editor. org/rfc 919. txt m Same as network broadcast if no subnetting Ø IP of network broadcast=Network. ID+(all 1’s for Host. ID) q 0. 0 m IP address of unassigned host (BOOTP, ARP, DHCP) m Default route advertisement 7

IP Addressing Problem #1 (1984) q Subnet addressing m http: //www. rfc-editor. org/rfc 917. txt m Address problem of inefficient use of address space m For class B & C networks Ø Class A (rarely given out, not many of them given out by IANA) Ø Class B = 64 k hosts o Very few LANs have close to 64 K hosts o Electrical/LAN limitations, performance or administrative reasons o e. g. , class B net allocated enough addresses for 64 K hosts, even if only 2 K hosts in that network Ø Class C = 256 hosts m Need simple way to get multiple “networks” Ø Use bridging, multiple IP networks or split up single network address ranges (subnet) Ø Reduce the total number of addresses that are assigned, but not used 8

Subnetting q Variable length subnet masks m Subnet a class B address space into several chunks Network Host Network Subnet 1111. . 1111 Host 0000 Mask 9

Subnetting Example q Assume an organization was assigned address 150. 100 q Assume < 100 hosts per subnet q How many host bits do we need? m Seven q What is the network mask? m 11111111 10000000 m 255. 128 10

IP Address Problem #2 (1991) q Address space depletion m In danger of running out of classes A and B m Class A Ø Very few in number Ø IANA frugal in giving them out m Class B Ø Subnetting only applied to new allocations Ø sparsely populated Ø people refuse to give it back m Class C too small for most domains Ø APNIC has only class C addresses 11

Some Solution q Solution m Assign multiple consecutive class C address blocks m Supernetting Ø http: //www. rfc-editor. org/rfc 1338. txt m Later known as Classless Inter-Domain Routing (CIDR) Ø http: //www. rfc-editor. org/rfc 1518. txt Ø http: //www. rfc-editor. org/rfc 1519. txt 12

IP addressing: CIDR q Classful addressing: m inefficient use of address space, address space exhaustion m e. g. , class B net allocated enough addresses for 65 K hosts, even if only 2 K hosts in that network q CIDR: Classless Inter. Domain Routing m network portion of address of arbitrary length m address format: a. b. c. d/x, where x is # bits in network portion of address network part host part 11001000 00010111 00010000 200. 23. 16. 0/23 13

IP addresses: how to get one? Q: How does host get IP address? q hard-coded by system admin in a file m Windows: control-panel->network->configuration->tcp/ip>properties m UNIX: /etc/rc. config m Linux (Redhat): /etc/sysconfig/network-script/ifcfg-eth q DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server m “plug-and-play” (more shortly) 14

IP addresses: how to get one? Q: How does network get network part of IP addr? A: gets allocated portion of its provider ISP’s address space ISP's block 11001000 00010111 00010000 200. 23. 16. 0/20 Organization 1 Organization 2. . . 11001000 00010111 00010000 11001000 00010111 00010010 0000 11001000 00010111 00010100 0000 …. 200. 23. 16. 0/23 200. 23. 18. 0/23 200. 23. 20. 0/23 …. Organization 7 11001000 00010111 00011110 0000 200. 23. 30. 0/23 15

Hierarchical addressing: route aggregation Hierarchical addressing allows efficient advertisement of routing information: Organization 0 200. 23. 16. 0/23 Organization 1 200. 23. 18. 0/23 Organization 2 200. 23. 20. 0/23 Organization 7 . . . Fly-By-Night-ISP “Send me anything with addresses beginning 200. 23. 16. 0/20” Internet 200. 23. 30. 0/23 ISPs-R-Us “Send me anything with addresses beginning 199. 31. 0. 0/16” 16

Hierarchical addressing: more specific routes ISPs-R-Us has a more specific route to Organization 1 Organization 0 200. 23. 16. 0/23 Organization 2 200. 23. 20. 0/23 Organization 7 . . . Fly-By-Night-ISP “Send me anything with addresses beginning 200. 23. 16. 0/20” Internet 200. 23. 30. 0/23 ISPs-R-Us Organization 1 200. 23. 18. 0/23 “Send me anything with addresses beginning 199. 31. 0. 0/16 or 200. 23. 18. 0/23” 17

Where to obtain IP address Q: How does an ISP get block of addresses? A: ICANN: Internet Corporation for Assigned Names and Numbers m allocates addresses m manages DNS m assigns domain names, resolves disputes 18

Outline q Overview of Network Layer q Network addressing Ø Network packet format and forwarding q NAT, DHCP, IPv 6 19

Getting a datagram from source to dest. forwarding table in A Dest. Net. next router Nhops 223. 1. 1 223. 1. 2 223. 1. 3 IP datagram: misc source dest fields IP addr data q datagram remains unchanged, as it travels source to destination q addr fields of interest here A B 223. 1. 1. 4 1 2 2 223. 1. 1. 1 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 E 223. 1. 3. 2 20

Getting a datagram from source to dest. forwarding table in A Dest. Net. next router Nhops misc data fields 223. 1. 1. 1 223. 1. 1. 3 223. 1. 1 223. 1. 2 223. 1. 3 Starting at A, send IP datagram addressed to B: q look up net. address of B in forwarding table q find B is on same net. as A q link layer will send datagram directly to B inside link-layer frame m B and A are directly connected A B 223. 1. 1. 4 1 2 2 223. 1. 1. 1 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 E 223. 1. 3. 2 21

Getting a datagram from source to dest. forwarding table in A Dest. Net. next router Nhops misc data fields 223. 1. 1. 1 223. 1. 2. 3 223. 1. 1 223. 1. 2 223. 1. 3 Starting at A, dest. E: q look up network address of E in forwarding table q E on different network m A, E not directly attached q routing table: next hop router to E is 223. 1. 1. 4 q link layer sends datagram to router 223. 1. 1. 4 inside link-layer frame q datagram arrives at 223. 1. 1. 4 q continued…. . A B 223. 1. 1. 4 1 2 2 223. 1. 1. 1 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 E 223. 1. 3. 2 22

Getting a datagram from source to dest. misc data fields 223. 1. 1. 1 223. 1. 2. 3 Arriving at 223. 1. 4, destined for 223. 1. 2. 2 q look up network address of E in router’s forwarding table q E on same network as router’s interface 223. 1. 2. 9 m router, E directly attached q link layer sends datagram to 223. 1. 2. 2 inside link-layer frame via interface 223. 1. 2. 9 q datagram arrives at 223. 1. 2. 2!!! (hooray!) forwarding table in router Dest. Net router Nhops interface 223. 1. 1 223. 1. 2 223. 1. 3 A B - 1 1 1 223. 1. 1. 4 223. 1. 2. 9 223. 1. 3. 27 223. 1. 1. 1 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 E 223. 1. 3. 2 23

IP datagram format IP protocol version number header length (bytes) “type” of data max number remaining hops (decremented at each router) upper layer protocol to deliver payload to how much overhead with TCP? q 20 bytes of TCP q 20 bytes of IP q = 40 bytes + app layer overhead 32 bits ver head. type of len service length fragment 16 -bit identifier flgs offset upper time to header layer live checksum total datagram length (bytes) for fragmentation/ reassembly 32 bit source IP address 32 bit destination IP address Options (if any) data (variable length, typically a TCP or UDP segment) E. g. timestamp, record route taken, specify list of routers to visit. 24

IP Fragmentation & Reassembly q network links have MTU (max. transfer size) - largest possible link-level frame. m different link types, different MTUs q large IP datagram divided (“fragmented”) within net m one datagram becomes several datagrams m “reassembled” only at final destination m IP header bits used to identify, order related fragments fragmentation: in: one large datagram out: 3 smaller datagrams reassembly 25

IP Fragmentation and Reassembly Example q 4000 byte datagram q MTU = 1500 bytes length ID fragflag offset =4000 =x =0 =0 One large datagram becomes several smaller datagrams length ID fragflag offset =1500 =x =1 =0 length ID fragflag offset =1500 =x =1 =1480 length ID fragflag offset =1040 =x =0 =2960 26

Fragmentation is Harmful q Uses resources poorly m Forwarding costs per packet m Best if we can send large chunks of data m Worst case: packet just bigger than MTU q Poor end-to-end performance m Loss of a fragment q Reassembly is hard m Buffering constraints 27

Avoid fragmentation q Path MTU Discovery in IP m http: //www. rfc-editor. org/rfc 1191. txt m Hosts dynamically discover minimum MTU of path m Algorithm: Ø Initialize MTU to MTU for first hop Ø Send datagrams with Don’t Fragment bit set Ø If ICMP “pkt too big” msg, decrease MTU m What happens if path changes? Ø Periodically (>5 mins, or >1 min after previous increase), increase MTU m Some routers will return proper MTU m MTU values cached in routing table 28

ICMP: Internet Control Message Protocol q used by hosts, routers, gateways to communication network-level information m error reporting: unreachable host, network, port, protocol m echo request/reply (used by ping) q network-layer “above” IP: m ICMP msgs carried in IP datagrams q ICMP message: type, code plus first 8 bytes of IP datagram causing error Type 0 3 3 3 4 Code 0 0 1 2 3 6 7 0 8 9 10 11 12 0 0 0 description echo reply (ping) dest. network unreachable dest host unreachable dest protocol unreachable dest port unreachable dest network unknown dest host unknown source quench (congestion control - not used) echo request (ping) route advertisement router discovery TTL expired bad IP header 29

Traceroute q Based on ICMP: provides delay measurement from source to router along end-end Internet path towards destination. m sends three packets that will reach router i on path towards destination m Set the TTL incrementally from 1 up to 30 m router i will return ICMP warning (type 11) back. m sender times interval between transmission and reply. TTL=1 TTL=3 TTL=2 30

Outline q Network addressing q Network packet format and forwarding Ø NAT, DHCP, IPv 6 31

NAT: Network Address Translation rest of Internet local network (e. g. , home network) 10. 0. 0/24 10. 0. 0. 1 10. 0. 0. 2 138. 76. 29. 7 10. 0. 0. 3 All datagrams leaving local network have same single source NAT IP address: 138. 76. 29. 7, different source port numbers Datagrams with source or destination in this network have 10. 0. 0/24 address for source, destination (as usual) 32

NAT: Network Address Translation q Motivation: local network uses just one IP address as far as outside word is concerned: m no need to be allocated range of addresses from ISP: just one IP address is used for all devices m can change addresses of devices in local network without notifying outside world m can change ISP without changing addresses of devices in local network m devices inside local net not explicitly addressable, visible by outside world (a security plus). 33

NAT: Network Address Translation Implementation A NAT router must: m 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. m remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair m 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 34

NAT: Network Address Translation 2: NAT router changes datagram source addr from 10. 0. 0. 1, 3345 to 138. 76. 29. 7, 5001, updates table 2 NAT translation table WAN side addr LAN side addr 1: host 10. 0. 0. 1 sends datagram to 128. 119. 40, 80 138. 76. 29. 7, 5001 10. 0. 0. 1, 3345 …… …… S: 10. 0. 0. 1, 3345 D: 128. 119. 40. 186, 80 S: 138. 76. 29. 7, 5001 D: 128. 119. 40. 186, 80 138. 76. 29. 7 S: 128. 119. 40. 186, 80 D: 138. 76. 29. 7, 5001 3: Reply arrives dest. address: 138. 76. 29. 7, 5001 3 1 10. 0. 0. 4 S: 128. 119. 40. 186, 80 D: 10. 0. 0. 1, 3345 10. 0. 0. 1 10. 0. 0. 2 4 10. 0. 0. 3 4: NAT router changes datagram dest addr from 138. 76. 29. 7, 5001 to 10. 0. 0. 1, 3345 35

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 an “on” Support for mobile users who want to join network (more shortly) DHCP overview: m host broadcasts “DHCP discover” msg m DHCP server responds with “DHCP offer” msg m host requests IP address: “DHCP request” msg m DHCP server sends address: “DHCP ack” msg 36

DHCP client-server scenario A B 223. 1. 1. 2 223. 1. 1. 4 223. 1. 1. 3 223. 1. 2. 1 DHCP server 223. 1. 1. 1 223. 1. 2. 9 223. 1. 3. 27 223. 1. 2. 2 223. 1. 3. 2 E arriving DHCP client needs address in this network 37

DHCP client-server scenario DHCP server: 223. 1. 2. 5 DHCP discover src : 0. 0, 68 dest. : 255, 67 yiaddr: 0. 0 transaction ID: 654 arriving client DHCP offer src: 223. 1. 2. 5, 67 dest: 255, 68 yiaddrr: 223. 1. 2. 4 transaction ID: 654 Lifetime: 3600 secs DHCP request time src: 0. 0, 68 dest: : 255, 67 yiaddrr: 223. 1. 2. 4 transaction ID: 655 Lifetime: 3600 secs DHCP ACK src: 223. 1. 2. 5, 67 dest: 255, 68 yiaddrr: 223. 1. 2. 4 transaction ID: 655 Lifetime: 3600 secs 38

IPv 6 q Initial motivation: 32 -bit address space completely allocated by 2008. q Additional motivation: m header format helps speed processing/forwarding m header changes to facilitate Qo. S m new “anycast” address: route to “best” of several replicated servers q IPv 6 datagram format: m fixed-length 40 byte header m no fragmentation allowed 39

IPv 6 Header (Cont) Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same “flow. ” (concept of“flow” not well defined). Next header: identify upper layer protocol for data 40

IPv 4 vs. IPv 6 type of ver head. len service total length fragment 16 -bit identifier flgs offset time to Internet protocol live checksum 32 bit source IP address 32 bit destination IP address Options (if any) data (variable length, typically a TCP or UDP segment) 41

Differences Between Ipv 4 and IPv 6 q Address length: 32 vs. 128 q Fragmentation: IPv 6 has no fragmentation q Type of service (TOS): IPv 6 has no TOS q Checksum: removed entirely to reduce processing time at each hop q Options: allowed, but outside of header, indicated by “Next Header” field; options specify how to deal with the packet if a header is unknown q ICMPv 6: new version of ICMP m additional message types, e. g. “Packet Too Big” m multicast group management functions 42

Transition From IPv 4 To IPv 6 q Not all routers can be upgraded simultaneous m no “flag days” m How will the network operate with mixed IPv 4 and IPv 6 routers? q Two proposed approaches: m Dual Stack: some routers with dual stack (v 6, v 4) can “translate” between formats m Tunneling: IPv 6 carried as payload in IPv 4 datagram among IPv 4 routers 43

Dual Stack Approach A B C D E F IPv 6 IPv 4 IPv 6 Flow: X Src: A Dest: F Flow: ? ? Src: A Dest: F data B-to-C: IPv 4 B-to-C: IPv 6 A-to-B: IPv 6 44

Tunneling Logical view: Physical view: A B IPv 6 A B C IPv 6 IPv 4 Flow: X Src: A Dest: F data A-to-B: IPv 6 E F IPv 6 D E F IPv 4 IPv 6 tunnel Src: B Dest: E Flow: X Src: A Dest: F data B-to-C: IPv 6 inside IPv 4 Flow: X Src: A Dest: F data E-to-F: IPv 6 45

Backup Slides 46

IP quality of service q IP originally had “type-of-service” (TOS) field to eventually support quality m Not used, ignored by most routers q Then came int-serv (integrated services) and RSVP signalling m Per-flow quality of service through end-to-end support Ø Setup and match flows on connection ID Ø Per-flow signaling Ø Per-flow network resource allocation (*FQ, *RR scheduling algorithms) 47

IP quality of service q RSVP m http: //www. rfc-editor. org/rfc 2205. txt m Provides end-to-end signaling to network elements m General purpose protocol for signaling information m Not used now on a per-flow basis to support int-serv, but being reused for diff-serv. q int-serv m Defines service model (guaranteed, controlled-load) Ø Dozens of scheduling algorithms to support these services Ø WFQ, W 2 FQ, STFQ, Virtual Clock, DRR, etc. Ø If this class was being given 5 years ago…. 48

IP quality of service q Why did RSVP, int-serv fail? m Complexity Ø Scheduling Ø Routing Ø Per-flow signaling overhead m Lack of scalability Ø Per-flow state Ø Route pinning m Economics Ø Providers with no incentive to deploy Ø SLA, end-to-end billing issues m Qo. S a weak-link property Ø Requires every device on an end-to-end basis to support flow 49

IP quality of service q Now it’s diff-serv… m Use the “type-of-service” bits as a priority marking m Core network relatively stateless m AF Ø Assured forwarding (drop precedence) m EF Ø Expedited forwarding (strict priority handling) 50

IPv 6 Addressing (standardized in 1995) q Length: 128 bits (RFC 1752) Provider-based unicast Link-local use unicast Site-local use unicast 3 n m o p 010 Registry Provider ID Subscriber ID Subnet ID 10 n 1111111010 0 10 n 1111111011 0 80 Embedded IPv 4 unicast Multicast q Interface ID 118 -n Interface ID m 118 -n-m Subnet ID 16 Interface ID 32 0000……………. . . 0000 IPv 4 address 80 16 32 0000……………. . . 0000 FFFF 8 1111 4 Flags IPv 4 address 4 112 Scope Group ID Anycast 51