The document provides an overview of IP addressing and routing, explaining concepts such as internet topology, addressing types, routing protocols, and special address conventions. It differentiates between classful and classless addressing, elaborates on subnetting, and identifies different types of routers and protocols used in routing information exchange. The document also discusses the significance of routing tables, metrics, and automatic vs. manual configuration in network routing.

1. IP Addressing and Introduction to IP routing Avgust Jauk <jauk@arnes.si> ARNES Bratislava, August 98

2. Agenda Internet topology Introduction to addressing Idea of routing Special address conventions Classfull addressing Classless addressing Routing protocols: IGPs and EGPs

3. Internet topology Internet - Network of Networks Networks Based on different technology Large or small Fast or slow Variety of connected nodes Routers (Gateways) Protocols

4. Internet topology

5. Routers Packet handling Packet forwarding Routing information processing Management Miscellaneous functions

6. Internet protocol stack

7. Internet protocol dependencies Hardware Users

8. Internet protocol dependencies Hardware Users

9. Layering in the Internet Application Transport Internet Network interface Application Transport Internet Network interface Internet Network interface Identical message Identical packet Identical datagram Identical datagram Identical frame Identical frame Physical Net 1 Physical Net 2 Gateway G Host A Host B

10. Internet datagram format

11. ICMP datagram format

12. ICMP Message types Type Field ICMP Message Type 0 Echo Reply 3 Destination Unreachable 4 Source Quench 5 Redirect (change a route) 8 Echo Request 11 Time Exceeded for Datagram 12 Parametere Problem on a Datagram 13 Timestamp Request 14 Timestamp Reply 15 Information Request (obsolete) 16 Information Reply (obsolete) 17 Address Mask Request 18 Address Mask Reply

13. Introduction to addressing Do I need an address? What types of addresses are there? Postal address Telephone number In Computer Networks: Physical Addresses (Ethernet, FDDI, ...) Textual Addresses - Names Network level addresses (IP, X.25,...)

14. Addressing in the Internet Address specifies host’s interface 32 bit addresses Network part & Host part Dotted decimal notation: 192.164.2.4 Network part Host part 0 31

15. Idea of routing Routers forward datagrams between connected networks They need to know via which interface to send a datagram Routing decisions are based on the information stored in the routing table

16. Routing table Tells where to send datagram for a particular network Network Next-Hop Port Metric 194.181.200.0 194.181.208.1 Eth0 1 193.2.1.0 194.181.208.320 Eth1 14 153.5.0.0 194.181.214.25 Fddi0 8 0.0.0.0 194.181.210.1 S0 5 Next-Hop routers must be directly reachable

17. Routing table (cont.) Default Route - a special entry in the routing table: “ Pass all datagrams for unknown networks to this router” Represented by the entry for network 0.0.0.0 Routing uses network part of the address!

18. Routing Algorithm Extract destination IP address from datagram Extract network address from the IP address If destination network equals my network Send directly to destination using physical network Else If destination address matches a host-specific route in the routing table: Send to the router specified in the routing table

19. Routing Algorithm (cont.) Else if destionation network matches a network in the routing table Send to the router specified in the routing entry Else If there is a default route in the routing table: Send to the router specified in the default route entry Else: Send a “No route to host” message to the source

20. Populating the Routing Table Manually by network administrator: Static Routes No dynamic changes to these routes will accur Dynamically by routing protocol Routing info is exchanged between routers The routing “metric” is used to find the best path

21. Static Routes Manually configured by network administrator A B

22. Static Routes Router cannot automatically reroute if path fails A B

23. Routing protocols Routers use a common protocol to exchange routing information Best path between networks or subnets is determined by “Routing Metric” Automatic adaption to topology changes

24. Routing protocols 64 kbps 64 kbps 2 Mbps 2 Mbps

25. Special address conventions Broadcast Addresses Directed broadcast: host part all 1’s - 194.181.200.255 Limited broadcast: all 1’s - 255.255.255.255 0 means “This” host part = 0 - this host network part = 0 - this network miss used as a broadcast address

26. Special address conventions (cont.) Loopback Address : 127.0.0.1 for testing and inter-process communication on the local machine should never appear on any network

27. Summary of special address conventions This host Limited broadcast (local net) Host on this net Directed broadcast for net Loopback all 0s all 0s host all 1s net 127 anything (often 1) all 1s

28. Classess and address formats 0 1 2 3 4 8 16 24 31 netid netid hostid hostid multicast address reserved for future use Class A Class C Class D Class E 0 0 0 0 netid hostid Class B 0 1 1 1 1 1 1 1 1 1 1

29. Classes: How to recognize them Class A: first byte in range 1-126 Class B: first byte in range 128-191 Class C: first byte in range 192-223 Class D: first byte in range 224-239 Class E: first byte in range 240-255

30. Classes: Size and Number Class A: 16.777.214 hosts, 128 networks Class B: 65.534 hosts, 16.324 networks Class C: 254 hosts, 2.097.152 networks

31. Problems with Classes Class A usually to big Class C often to small Not enough Class Bs Inefficient utilisation of address space Solution: extending the network part of the address: Subnetting

32. Subnetting Class B 0 1 Class B 0 1 Class B Address: Before Subnetting Class B Address: After Subnetting Network Network Host Host Subnet

33. Subnet mask Subnet mask defines the network part binary 1 in network bits binary 0 in hosts bits Subnet mask must be contiguous! Network part Host part 0 31 1 ..... 1 0 ...... 0

34. Subnetting (cont.) Not limited to byte border Subnets “0” and “-1” used to be reserved Subnet “0” : this subnet Subnet “-1”: broadcast Network administrator decides on the subnet size Network and subnet numbers used for routing decisions

35. Subnetting and routing one subnet mask per particular class routing considerations all subnets of the same class must be contiguous or static routes must be used or routing protocol must carry also subnet masks

36. Subnetting and routing all subnets of the same class must be contiguous! C 1 1 C 1 2 B C 1 4 C 1 3 C 1 C 1

37. Subnet mask bits 128 64 32 16 8 4 2 1 1 0 0 0 0 0 0 0 = 128 1 1 0 0 0 0 0 0 = 192 1 1 1 0 0 0 0 0 = 224 1 1 1 1 0 0 0 0 = 240 1 1 1 1 1 0 0 0 = 248 1 1 1 1 1 1 0 0 = 252 1 1 1 1 1 1 1 0 = 254 1 1 1 1 1 1 1 1 = 255

38. Binary Numbers = 128 + 64 + 32 + 2 128 64 32 16 8 4 2 1 Represent 226 decimal in binary: = 6 2 1 1 1 0 0 0 1 0 6 2 226 = 2 7 2 5 2 4 2 3 2 2 1 2 0 2 2 2 7 2 5 2 4 2 3 2 2 1 2 0 2 2

39. Subnetting a Class C split subnet mask # subnets # hosts/subnet total # hosts utilis. 1:7 128 2 252 126 99% 2:6 192 4 248 62 98% 3:5 224 8 240 30 94% 4:4 240 16 14 224 88% 5:3 248 32 6 192 76% 6:2 252 64 2 128 50% 7:1 254 / / / /

40. Variable Length Subnet Masks (VLSM) Subnets are of different size A means for conserving address space How to do it: how big is the biggest subnet? split the class into such pieces split (“sub-subnet” ) those peieces further

41. VLSM (cont.) How to do VLSM 0 255

42. VLSM and routing Prerequisites: routing protocol must carry subnet masks or static routes must be used

43. Classfull Addressing: drawbacks Classfull Addressing + Subnetting at least one route per class is advertised in routing updates Number of networks is doubling faster than once per year Memory is not growing that fast Only a few routers can keep the current number of routes Route flapping

44. Classless addressing Introduced by CIDR - Classless InterDomain Routing Networks are grouped (aggregated) into blocks Blocks of networks are advertised New way of thinking: there are no networks numbers, but just address space prefixes there are no subnet masks, just prefix lenghts

45. Classless addresses notation 10.181.215.32 /27 10.181.215.32 with mask 255.255.255.224 binary representation of mask: 11111111.11111111.11111111.11100000

46. Classless address notation Hosts . . . 8 16 32 64 128 256 . . . 4096 8192 16384 32768 65535 . . . Prefix . . . /29 /28 /27 /26 /25 /24 . . . /20 /19 /18 /17 /16 . . . Classful . . . 1 C . . . 16 C’s 32 C’s 64 C’s 128 C’s 1 B . . . Subnet Mask . . . 255.255.255.248 255.255.255.240 255.255.255.224 255.255.255.192 255.255.255.128 255.255.255.0 . . . 255.255.240.0 255.255.224.0 255.255.192.0 255.255.128.0 255.255.0.0 . . .

47. Classless network aggregation - Supernetting Class C 24-bit prefix 11000000 192 168 64 0 10101000 01000000 Prefix Host part 00000000 Common prefix: 23 bits 11111111 11111111 1111111 0 00000000 00000000 Classless 23-bit prefix 11000000 192 168 64 /23 10101000 0100000 0 00000000 Class C next 24-bit prefix 11000000 192 168 65 0 10101000 01000001 00000000

48. Classless network aggregation (cont.) Before aggregation 201.222.191.0/24 201.222.192.0/24 201.222.193.0/24 After aggregation 201.222.191.0/24 201.222.192.0/23

49. Classless addressing and routing Longest match routing Route distr. between two protocols, one is not supporting classless use a default route “ explode” supernet info. into individual network numbers

50. Classes of routing protocols The early Arpanet was completelly flat - single “network” model one routing protocol, all routers had all the routing info with the growth it become hard to maintaine and computationally intensive Solution: split the Internet into a set of Autonomous Systems (AS) Each Autonomous System is a set of routers and networks under the same administration

51. Classes of routing protocols (cont.) Special routers, called “Exterior gateways” used to connect ASes Two classes of routing protocols: Interior routing protocols (IGP - Interior Gateway protocols) Exterior routing protocols (EGP - Exterior Gateway protocols)

52. Interior Routing Protocols (IGPs) Used inside an Autonomous System Designed to handle more redundant links Links are cheaper in a local environment => one can afford more redundant links Designed with a higher bandwidth in mind Cheaper bandwidth => one can use more bandwidth for the exchange of routing information

53. Interior Routing Protocols (cont.) They generally contaion less ingformation than EGPs IGPs in general (with exeptions) do not have to know about any other network outside the AS No policy support Inside AS, one generally does not want to aplly policy everyone can use every available link policies are generally only set on what links should be preffered

54. Interior Routing Protocols (cont.) Fairly extensive metric support Redudancy => one has to distinguish between redundant links metrics or “costs” help in the decision proccess Designed for fast convergence Because of the redudancy, IGPs are designed to make quick changes if the network topology changes

55. Exterior Routing Protocols (EGPs) Used to exchange routing information between ASes Designed with lower bandwidth in mind long distance links are more expensive => routing protocol should use less bandwidth for the exchange of routing information They generally contain a lot of information EGPs have to know about all external networks In the Internet that might be 40.000 networks

56. Exterior Routing Protocols (cont.) They assume a less reliable network most of them are connection oriented for reliable delivery They are designed to provide policy control generally you set routing policy at the border of your routing domain They do not run in every single router Only at the border of your AS you have to run an EGP Internal routers can be less powerfull

57. Summary We have covered Internet topology Routing: static, dynamic classes of routing protocols Addressing classfull subnetting VLSM classless

58. Where to get more information RFC´s (RFC-1880: Internet Official Protocol Standards) Books D.C.Lynch, M.T.Rose: Internet System Handbook D.E.Comer: Internetworking with TCP/IP Mailing lists Usenet News

59. Network troubleshooting Ping: ICMP echo-request Traceroute UDP to an non-existing port start with TTL=1 increase by 1 can get back: ICMP time exceeded ICMP port unreachable TCPdump, trace utilities in routers, ...

60. Track 1: Initial configuration Domain name: ceews.ceu.hu PC names: tr1pcxy x : row number (1 to 7) y : a number of a PC inside a row (1 to 3) IP address: 193.225.220.(x*8+y) Network mask: 255.255.255.0 Default Gateway: 193.225.220.1 DNS: 193.225.218.100

61. Domain Name System Domain Names: vislava.ceenet.waw.pl IP addresses: 194.181.200.2 Need for automatic conversion Conversion table (/etc/hosts) Distributed Hierarhical Database Client-Server model: Server: Name Server Client: Name Resolver