IP Internet Protocol IP is the workhorse protocol

IP: Internet Protocol • IP is the workhorse protocol of the TCP/IP protocol suite • IP provides an unreliable, connectionless, datagram delivery service • The internet protocol implements two basic functions: addressing and fragmentation. • RFC 791 is the official specification of IP 11/2/2020 Internet Protocol 1

The Workhorse User Process TCP 11/2/2020 User Process UDP transport ICMP IP IGMP ARP Hardware Interface RARP Internet Protocol application network link 2

IP Header 8 16 Version Hdr Len Type of Service Identification Time to Live 31 Total Length (in bytes) Flags Protocol Fragment offset Checksum 20 bytes Source IP Address Destination IP Address options (if any) data 11/2/2020 Internet Protocol 3

Network Byte Ordering • Multi-byte numbers can be stored in one of two ways: – 6000010 = 00000000 11101010 01100000 • Network byte order is big endian 11/2/2020 Internet Protocol 4

IP Header Fields 11/2/2020 Internet Protocol 5

Type of Service • The IP protocol provides a (rather limited) facility for upper layer protocols to convey hints to the Internet Layer about how the tradeoffs should be made for the particular packet 3 -bit precedence 11/2/2020 4 -bit TOS Internet Protocol MBZ 6

TOS Field Values • There are 4 defined values for the TOS field • Note these values are defined as integers, not as bits 11/2/2020 Internet Protocol 7

Recommended TOS Values 11/2/2020 Internet Protocol 8

Fragmentation • The physical layer often imposes an upper limit on the size of the frame that can be transmitted • IP compares the MTU with the datagram size and performs fragmentation, if necessary • Fragmentation can take place at the original host or at an intermediate router • IP datagrams are not reassembled until they reach their final destination 11/2/2020 Internet Protocol 9

Fragmentation and the Header • The following fields are used in fragmentation – identification • contains a unique value for each IP datagram that the sender transmits – flags MBZ Don’t fragment More fragments – fragment offset • the offset of the fragment from the beginning of the original datagram 11/2/2020 Internet Protocol 10

Fragmentation • If fragmentation must occur… – if the “don’t fragment” bit is turned on the packet is discarded – the packet is split into fragments • the header is basically copied except for… – total length is changed to the size of the fragment – the fragmentation offset is set to the offset of the fragment from the beginning of the original datagram – the “more fragments” bit is turned on in every fragment except for the last one 11/2/2020 Internet Protocol 11

Reassembly • The identification field is used to ensure that fragments of different datagrams are not mixed. • The fragment offset field tells the receiver the position of a fragment in the original datagram • The fragment offset and length determine the portion of the original datagram covered by this fragment • The more-fragments flag indicates (by being reset) the last fragment 11/2/2020 Internet Protocol 12

Protocol Field • This field indicates the next level protocol used in the data portion of the internet datagram • The values for various protocols are specified in RFC 1060 (Assigned Numbers) 11/2/2020 Internet Protocol 13

Header Checksum • The header checksum is calculated over the IP header only • The checksum is calculated as follows: – set the checksum field to 0 – calculate the 16 -bit one’s complement sum of the header – the 16 -bit one’s complement of this sum is stored in the checksum field 11/2/2020 Internet Protocol 14

Header Checksum • When an IP datagram is received, the 16 -bit one’s complement sum of the header is calculated • Since the receiver’s calculated checksum contains the checksum stored by the sender, the calculated result should be all ones • If the checksum is wrong, the packet is quietly discarded. No error messages are generated • ICMP, IGMP, UDP, and TCP all use the same checksum 11/2/2020 Internet Protocol 15

Addressing • A distinction is made between names, addresses, and routes – A name indicates what we seek – An address indicates where it is – A route indicates how to get there • The internet protocol deals primarily with addresses. It is the task of higher level protocols to make the mapping from names to addresses. 11/2/2020 Internet Protocol 16

IP Addresses • Every interface on the internet must have a unique Internet Address (also called an IP address) • IP addresses are 32 -bits numbers • The addresses are not flat, they are divided into two components: the host address and the network address • The number of bits assigned to the host portion and network portion of the address varies depending on the class of the address 11/2/2020 Internet Protocol 17

IP Address Classes 7 bits Class A Class B Class C 0 1 1 24 bits netid hostid 0 14 bits 16 bits netid hostid 21 bits 8 bits netid hostid 28 bits Class D 1 1 1 0 multicast group ID 27 bits Class E 1 11/2/2020 1 1 1 0 (reserved for future use) Internet Protocol 18

Dotted Decimal Notation • IP addresses are normally written as four decimal numbers, one for each byte of the address. – 129. 21. 38. 169 • The easiest way to differentiate between the classes is to look at the first number 11/2/2020 Internet Protocol 19

Assigning IP Addresses • Since every interface must have a unique IP address, there must be a central authority for assigning numbers • That authority is the Internet Network Information Center, called the Inter. NIC. • The Inter. NIC assigns only network ids, the assignment of host ids is up to the system administrator 11/2/2020 Internet Protocol 20

Subnet Addressing • The original view of the Internet universe was a two-level hierarchy: – the top level the Internet as a whole – the level below it individual networks, each with its own network number. • In this two-level model, each host sees its network as a single entity 11/2/2020 Internet Protocol 21

Subnet Addressing • While the two-level view has proved simple and powerful, a number of organizations have found it inadequate, and have added a third level to the interpretation of Internet addresses. • In this view, a given Internet network is divided into a collection of subnets. • The three-level model is useful in networks belonging to moderately large organizations 11/2/2020 Internet Protocol 22

Subnet Addressing • Locally IP addresses consist of three parts: – network ID – subnet ID – host ID • Outside of the subnetted network the addresses are handled normally • Inside the subnet, the network portion of the address is extended for local routing purpose 11/2/2020 Internet Protocol 23

Subnet Masks • Once the decision to subnet has been made, the local administrator must decide how many bits to allocate to the subnet ID • A common division is to use the 8 -bit boundary in the 16 bits of a host ID in a class B address • A subnet mask is used to divide the local address into network and host portions • Subnetting effectively hides the details of the internal network to external routers 11/2/2020 Internet Protocol 24

Special IP Addresses 11/2/2020 Internet Protocol 25

IP Options Field • The options field is a variable-length list of optional information for the datagram • The options currently defined are – – security and handling restrictions (RFC 1108) record route timestamp loose & strict source routing • The options field always ends on a 32 -bit boundary 11/2/2020 Internet Protocol 26

IP Routing • Routing is one of the most important functions of IP • Datagrams to be routed can either be generated on the local host or on some other host • If a machine is not configured as a router, datagrams received through network interfaces that are not addressed to the machine are dropped 11/2/2020 Internet Protocol 27

Host Routing • Conceptually IP routing is easy, especially for a host – Remember the structure of an internet address • If the destination is directly connected to the host, or on a shared network, then the datagram is sent directly • Otherwise the host sends the datagram to a default router, and lets the router do all of the work 11/2/2020 Internet Protocol 28

IP routing Algorithm • The basic internet routing algorithm is used by both hosts and routers • The primary difference is that hosts never forward datagrams (except to a default router), whereas routers forward datagrams • The algorithm uses a routing table to make routing decisions 11/2/2020 Internet Protocol 29

A Typical Routing Table • Each entry in the routing table contains the following information – Destination IP address. • this can be either a host address or a network address – IP address of the next-hop router, or the IP address of a directly connected network – Flags that tell more about the entry – Which interface the datagram should be passed to for delivery 11/2/2020 Internet Protocol 30

IP routing • IP routing performs the following actions – search the routing table for an entry that matches the complete destination address. If found, send the packet as indicated – search the routing table for a matching destination network ID. If found, send the packet as indicated – search the routing table for a default entry. If found send the packet as indicated • If none of the steps work, the datagram is undeliverable 11/2/2020 Internet Protocol 31

IP Layer Routing 11/2/2020 Internet Protocol 32

IP Routing • The routing done by IP, when it searches the routing table and decides which interface to send a packet out, is a routing mechanism • A routing policy is a set of rules that determines which routes go into the routing table. • IP performs the routing mechanism while a routing daemon normally provides the routing policy. 11/2/2020 Internet Protocol 33

Initializing a Routing Table • One common way is to execute the route command explicitly from the initialization files when the system is being bootstrapped. • Some systems allow a default router to be specified in a file such, and this default is added to the routing table on every reboot. • Other ways to initialize a routing table are to run a routing daemon or to use the newer router discovery protocol. 11/2/2020 Internet Protocol 34

Routing Errors • What happens if there is no default route, and a match is not found for a given destination? • If the datagram was generated locally, an error is returned to the application that sent the datagram (either “host unreachable” or “network unreachable”) • What do I do if I am a router? – Sender should be notified of the error 11/2/2020 Internet Protocol 35

Internet Control Message Protocol • ICMP communicates error messages and other conditions that require attention • ICMP is often considered part of the IP layer • RFC 792 is the official specification for ICMP • ICMP messages are transmitted within IP datagrams 11/2/2020 Internet Protocol 36

ICMP Packet Format • The first 4 bytes of the same format for all messages, the remainder differs from one message to the next 8 -bit type 8 -bit code 16 -bit checksum contents depend on type and code 11/2/2020 Internet Protocol 37

ICMP Message Types 11/2/2020 Internet Protocol 38

ICMP Message Types 11/2/2020 Internet Protocol 39

ICMP Error Messages • When an ICMP error message is sent, the message always contains the IP header and the first 8 bytes of the IP datagram that caused the problem • ICMP has rules regarding error message generation to prevent broadcast storms 11/2/2020 Internet Protocol 40

Error Message Generation Rules • ICMP errors messages are not generated in response to – – – 11/2/2020 an ICMP error message datagrams destined to an IP broadcast address datagrams sent as a link-layer broadcast a fragment other than the first a datagram whose source address does not define a single host Internet Protocol 41

ICMP Timestamp Request & Reply • This option allows a system to query another for the current time. • The recommended value to be returned is the number of milliseconds since midnight, Coordinated Universal Time (UTC). • A drawback is that only the time since midnight is returned. The caller must know the date form some other means 11/2/2020 Internet Protocol 42

Timestamp Message Format type (13 or 14) code (0) identifier (can be set to anything) 16 -bit checksum sequence (can be set to anything) 32 -bit originate timestamp 32 -bit receive timestamp 32 -bit transmit timestamp 11/2/2020 Internet Protocol 43

Time Adjustments • The time fields are defined as follows – originate: time the request is sent – receive: time the request is received by the receiver – transmit: time the reply is sent originate received request reply transmit RTT • Adjustment: (recv - orig) - (0. 5 * RTT) 11/2/2020 Internet Protocol 44

ICMP Unreachable Error • Unreachable errors are generate for a number of reasons – network unreachable – host unreachable type (3) code (0 -15) 16 -bit checksum unused (must be 0) IP header (including options) + first 8 bytes of IP datagram data 11/2/2020 Internet Protocol 45

Handling of ICMP Messages 11/2/2020 Internet Protocol 46

Handling of ICMP Messages 11/2/2020 Internet Protocol 47

ICMP Redirect Errors • The ICMP redirect error is sent by a router to a sender of an IP datagram when the datagram should have been sent to a different router. 11/2/2020 Internet Protocol 48

Sending a Redirect • How can a router make this decision? – Assume a host sends an IP datagram to R 1. This routing decision is often made because R 1 is the default router – R 1 receives the datagram and determines that R 2 is the next-hop router – When it sends the datagram to R 2, R 1 detects that it is sending it out the same interface on which the datagram arrived. – R 1 sends an ICMP redirect to the host, telling it to send future datagrams to that destination to R 2 11/2/2020 Internet Protocol 49

Using Redirects • A common use for redirects is to let a host with minimal routing knowledge build up a better routing table over time. • The host can start with a default route and anytime this turns out to be wrong, it will be informed by that router with a redirect, allowing the host to update its routing tables accordingly. 11/2/2020 Internet Protocol 50

Redirect Rules • There are rules regarding the generation of ICMP redirects. – Redirects are generated only by routers, and not by hosts – Redirects are intended to be used by hosts, not by routers (it is assumed that routers participate in a routing protocol with other routers, and the routing protocol eliminates the needs for redirects) 11/2/2020 Internet Protocol 51

Handling Redirects • A host that receives an ICMP redirect performs some checks before modifying its routing table – the new router must be on a directly connected network – the redirect must be from the current router for that destination – the redirect cannot tell the host to use itself as the router – the route that is being modified must be a direct route • Routers should send only host redirects and not network redirects 11/2/2020 Internet Protocol 52

ICMP Router Discovery • A newer way to initialize a routing table is to use the ICMP router advertisement and solicitation • The general concept is that after bootstrapping, a host broadcasts or multicasts a router solicitation message. One or more routers respond with a router advertisement message • Routers periodically broadcast or multicast their router advertisements • RFC 1256 specifies the format of these messages 11/2/2020 Internet Protocol 53

Message Formats 11/2/2020 Internet Protocol 54

Router Discovery Messages • Multiple addresses can be advertised by a router in a single message – number of addresses gives the number of addresses in the message – address entry size is the number of 32 -bit words for each router address and is always 2 – lifetime is the number of seconds that the advertised addresses can be considered valid 11/2/2020 Internet Protocol 55

Router Discovery Messages • Pair(s) of IP addresses and a preference then follow (the address must be router's IP address) • The preference level indicates the preference of this address as a default router – Larger values imply more preferable addresses. – The preference level 0 x 80000000 indicates that the corresponding address, although advertised, should not be used by the receiver as a default router address – The default value is normally 0. 11/2/2020 Internet Protocol 56

Router Discovery Operation • When a router starts up it transmits periodic advertisements on all interfaces capable of broadcasting or multicasting • The default lifetime for a given advertisement is 30 minutes. • The lifetime field is is also used when an interface on a router is disabled. In this case the router transmits an advertisement with lifetime set to 0. 11/2/2020 Internet Protocol 57

Router Discovery Operation • A router also listens for solicitations from hosts. It responds to these solicitations with a router advertisement. • If there are multiple routers on a subnet, it is up to the system administrator to configure the preference level for each router as appropriate. For example a primary router would have a higher preference than a backup. 11/2/2020 Internet Protocol 58

Host Discovery Operation • Upon bootstrap a host normally transmits three router solicitations, 3 seconds apart • A host listens for advertisements from adjacent routers. These advertisements can cause the host's default router to change • If an advertisement is not received for the current default, that default can timeout – A router will send advertisements every 10 minutes, with a lifetime of 30 minutes 11/2/2020 Internet Protocol 59

CS Network 129. 21. 38. 254 mordor-38 129. 21. 38. 218 129. 21. 37. 254 mordor-39 129. 21. 37. 218 129. 21. 39. 218 129. 21. 30. 26 ICL 1 ICL 4 Grad Lab servers silver 129. 21. 38. 145 129. 21. 37. 175 11/2/2020 129. 21. 30. 254 mordor-37 kiev staff 129. 21. 39. 254 ICL 2 ICL 3 CSL Internet Protocol mordor 60

Kiev ifconfig kiev> ifconfig -a lo 0: flags=849<UP, LOOPBACK, RUNNING, MULTICAST> mtu 8232 inet 127. 0. 0. 1 netmask ff 000000 hme 0: flags=863<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST> mtu 1500 inet 129. 21. 38. 145 netmask ffffff 80 broadcast 129. 21. 38. 255 kiev> 11/2/2020 Internet Protocol 61

Mordor ifconfig mordor> ifconfig -a lo 0: flags=849<UP, LOOPBACK, RUNNING, MULTICAST> mtu 8232 inet 127. 0. 0. 1 netmask ff 000000 hme 0: flags=863<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST> mtu 1500 inet 129. 21. 30. 26 netmask ffffff 80 broadcast 129. 21. 30. 127 qfe 0: flags=863<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST> mtu 1500 inet 129. 21. 37. 218 netmask ffffff 80 broadcast 129. 21. 37. 255 qfe 1: flags=863<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST> mtu 1500 inet 129. 21. 38. 218 netmask ffffff 80 broadcast 129. 21. 38. 255 qfe 2: flags=863<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST> mtu 1500 inet 129. 21. 39. 218 netmask ffffff 80 broadcast 129. 21. 39. 255 mordor> 11/2/2020 Internet Protocol 62

Grace ifconfig $ ifconfig -a tu 0: flags=c 63<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST, SIMPLEX> fta 0: flags=8 c 63<UP, BROADCAST, NOTRAILERS, RUNNING, MULTICAST, SIMPLEX> inet 129. 21. 3. 102 netmask ffffff 00 broadcast 129. 21. 3. 255 ipmtu 4352 sl 0: flags=10<POINTOPOINT> lo 0: flags=100 c 89<UP, LOOPBACK, NOARP, MULTICAST, SIMPLEX, NOCHECKSUM> inet 127. 0. 0. 1 netmask ff 000000 ipmtu 4096 11/2/2020 Internet Protocol 63

Kiev netstat kiev> netstat -rn Routing Table: Destination ----------129. 21. 38. 128 224. 0. 0. 0 default 127. 0. 0. 1 kiev> 11/2/2020 Gateway Flags Ref Use Interface ---------- --------129. 21. 38. 145 U 3 3056 hme 0 129. 21. 38. 145 U 3 0 hme 0 129. 21. 38. 254 UG 0 21129 127. 0. 0. 1 UH 0 21718 lo 0 Internet Protocol 64

Mordor netstat mordor> netstat -rn Routing Table: Destination ----------129. 21. 30. 0 129. 21. 37. 128 129. 21. 38. 128 129. 21. 39. 128 224. 0. 0. 0 default 127. 0. 0. 1 mordor> 11/2/2020 Gateway Flags Ref Use Interface ---------- --------129. 21. 30. 26 U 3 374 hme 0 129. 21. 37. 218 U 2 2667 qfe 0 129. 21. 38. 218 U 2 2858 qfe 1 129. 21. 39. 218 U 2 1967 qfe 2 129. 21. 30. 26 U 3 0 hme 0 129. 21. 30. 126 UG 0 4762 127. 0. 0. 1 UH 08072949 lo 0 Internet Protocol 65

traceroute kiev> traceroute silver traceroute: Warning: ckecksums disabled traceroute to silver (129. 21. 37. 175), 30 hops max, 40 byte packets 1 cs 3 -router (129. 21. 38. 254) 0. 716 ms 0. 513 ms 0. 523 ms 2 silver (129. 21. 37. 175) 1. 703 ms * 0. 988 ms kiev> traceroute mordor traceroute: Warning: ckecksums disabled traceroute to mordor (129. 21. 30. 26), 30 hops max, 40 byte packets 1 cs 3 -router (129. 21. 38. 254) 0. 635 ms 0. 496 ms 0. 527 ms 2 mordor-38 (129. 21. 38. 218) 0. 590 ms * 0. 746 ms kiev> traceroute mordor-38 traceroute: Warning: ckecksums disabled traceroute to mordor-38 (129. 21. 38. 218), 30 hops max, 40 byte packets 1 mordor-38 (129. 21. 38. 218) 0. 558 ms * 0. 457 ms kiev> 11/2/2020 Internet Protocol 66

traceroute kiev> traceroute grace traceroute: Warning: ckecksums disabled traceroute to grace. rit. edu (129. 21. 3. 102), 30 hops max, 40 byte packets 1 cs 3 -router (129. 21. 38. 254) 0. 730 ms 0. 572 ms 0. 442 ms 2 grace. isc. rit. edu (129. 21. 3. 102) 0. 794 ms 0. 724 ms 0. 697 ms kiev> $ traceroute kiev. cs. rit. edu traceroute to kiev. cs. rit. edu (129. 21. 38. 145), 30 hops max, 40 byte packets 1 r 33. isc. rit. edu (129. 21. 3. 217) 1 ms 0 ms 2 kiev. cs. rit. edu (129. 21. 38. 145) 1 ms * 1 ms $ 11/2/2020 Internet Protocol 67

PTT-net • Recently got Road Runner • Unhappy about reports of constant probes of machines • Policy decision – I want to prevent unauthorized probes/connection attempts on my machines • Mechanism – Purchase some sort of firewall for my home network 11/2/2020 Internet Protocol 68

DI-701 Manufacturer: D-Link (www. dlink. com) 11/2/2020 Internet Protocol 69

Configuration Desktop Internet Cable Modem DI-701 Hub Laptop Printer 11/2/2020 Internet Protocol 70

Address Management RR-DHCP (24. 93. 24. 121) Internet Cable Modem Desktop DI-701 Hub DLINK (192. 168. 0. 1) Laptop Printer DLINK-DHCP (192. 168. 0. 2 – 192. 168. 0. 32) 11/2/2020 Internet Protocol 71

Firewall Internet traffic stops here Internet Cable Modem Desktop DI-701 Filters Internet traffic… 11/2/2020 Internet Protocol Hub Laptop Printer Addresses never go past firewall 72

BCP-5 • The Internet has grown beyond anyone's expectations. Sustained exponential growth… • One challenge is that globally unique address space will be exhausted. • A separate and far more pressing concern is that the amount of routing overhead will grow beyond the capabilities of Internet Service Providers. • Efforts are in progress to find long term solutions to both of these problems. 11/2/2020 Internet Protocol 73

Types of Hosts • Hosts using IP can be grouped into 3 categories: – Category 1 • Hosts that do not require access to hosts in other enterprises or the Internet at large – Category 2 • Hosts that need access to a limited set of outside services which can be handled by mediating gateways. For many hosts in this category an unrestricted external access may be unnecessary and even undesirable for security reasons. – Category 3: • Hosts that need network layer access outside the enterprise (provided via IP connectivity) 11/2/2020 Internet Protocol 74

Ramifications • Hosts using IP can be grouped into 3 categories: – Category 1 • IP addresses need to be unambiguous within an enterprise, but may be ambiguous between enterprises. – Category 2 • Just like hosts within the first category, hosts may use IP addresses that are unambiguous within an enterprise, but may be ambiguous between enterprises. – Category 3: • Requires IP addresses that are globally unambiguous. 11/2/2020 Internet Protocol 75

PTT-net • PTT-net clearly falls into category 1 or 2 – Assuming the DI-701 is doing its job • The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets: – 10. 0 - 10. 255 – 172. 16. 0. 0 - 172. 31. 255 – 192. 168. 0. 0 - 192. 168. 255 11/2/2020 Internet Protocol 76

Mystery • PTT’s laptop opens a TCP connection to the CS department’s web server – – – – 11/2/2020 Laptop’s address is 192. 168. 0. 2: 1234 Destination is 129. 21. 30. 29: 80 Routed to DI-701 replaces with address with 24. 93. 24. 121 RIT responds, destination 24. 93. 24. 121 Arrives at DI-701 How does the DI-702 know the send the packet to the laptop? Internet Protocol 77

Mystery Solved Private Address Private Port External Address External Port NAT Port Protocol Used 192. 168. 0. 2 1234 129. 21. 30. 21 80 14003 TCP 192. 1. 68. 0. 1 386 129. 2. 1. 30. 21 80 14004 TCP 192. 168. 0. 2 5000 129. 21. 30. 24 25 14005 TCP 192. 168. 0. 1 5000 129. 21. 30. 24 25 14006 TCP 11/2/2020 Internet Protocol 78

Network Address Translator • NAT is a method by which IP addresses are mapped from one realm to another • NAT devices connect an isolated address realm to a realm with globally unique registered addresses • There a variety of flavors of NAT and terms to match them • RFC-2663 is an attempt to define NAT 11/2/2020 Internet Protocol 79

Common Characteristics • All flavors of NAT devices should share the following characteristics. – Transparent Address assignment. – Transparent routing through address translation. (routing here refers to forwarding packets, and not exchanging routing information) – ICMP error packet payload translation. 11/2/2020 Internet Protocol 80

Basic Idea • NAT devices attempt to provide transparent routing – Source/Destination addresses are modified en-route – The NAT device maintains state so that the datagrams are routed to the correct end-node – This solution works only when the applications do not use the IP addresses as part of the protocol itself 11/2/2020 Internet Protocol 81

Translation • TCP/UDP sessions are uniquely identified by the tuple – (source-IP, source-port, dest-IP, dest-port) • ICMP query sessions are identified by – (source-IP, ICMP query ID, dest-IP) • All other sessions – (source-IP, dest-IP, IP protocol) 11/2/2020 Internet Protocol 82

Start of Session • TCP – The first packet of every sessions contains a SYN bit and no ACK bit – All other TCP packets will have the ACK bit set • UDP – No deterministic way to determine the start of a session – Assume the first packet with never before seen parameters marks the start of a session 11/2/2020 Internet Protocol 83

IP Futures • There are problems with IP which are a result of the phenomenal growth of the Internet over the past few years – as of 1994, over half of the class B addresses have been allocated – 32 -bit IP addresses are inadequate – the current routing structure is basically flat, making routing tables too large • CDIR fixes the last problem for a while 11/2/2020 Internet Protocol 84

New IP Versions • Four proposals have been made for a new version of IP – SIP, the Simple Internet Protocol. Proposes a minimal set of changes to IP that uses 64 -bit addresses and a different header format – PIP, larger, variable length, hierarchical addresses with a different header format – TUBA (RFC 1347), TCP and UDP with bigger addresses – TP/IX (RFC 1475), 64 -bit addresses, changes TCP/UDP 11/2/2020 Internet Protocol 85

References • The May 1993 issue of IEEE Network (volume 7, number 3) contains overviews of the first three proposals, along with an article on CDIR. • RFC 1454 also compares the first three proposals 11/2/2020 Internet Protocol 86