End-to-end principle by Dave Clark Hop-by-hop control vs. - PDF document

Introduction to routing in the Internet Internet architecture IPv4, ICMP, ARP Addressing, routing principles (Chapters 2–3 in Huitema) Internet-1 S-38.2121 / Fall-06 / RKa, NB Internet Architecture Principles End-to-end principle by Dave Clark • Hop-by-hop control vs. End-to-end control – In X.25 – In IP – Error and flow control on each hop – Error and flow control in end station • The network can not be trusted • The user must in any case check for errors ÿ Network control is redundant • Error checking and flow control by TCP in the end stations • No state information in the network – The network is not aware of any connections – Packets routed independently – If a link fails, another route is used • Same principle as in distributed systems Internet-3 S-38.2121 / Fall-06 / RKa, NB 1

Internet Architecture Principles by Vinston Cerf IP over everything • Internet connects different types of networks – Each with different framing, addressing, … Interconnection based on translation Interconnection based on overlay • Mapping through a gateway • Approach used by IP • Never perfect • Single protocol over all underlying networks • Simple to adapt to new technologies – Define framing or encapsulation – Define address resolution: IP- address ÿ network address • Unique IP-address Translation still needed in many cases E.g. signaling interworking, IPv4 to IPv6 mapping Internet-4 S-38.2121 / Fall-06 / RKa, NB Internet Architecture Principles IP over everything HTTP, FTP, IMAP, SMTP, ... TCP, UDP, ... IP IEEE-802, ATM, X.25, ... Internet-5 S-38.2121 / Fall-06 / RKa, NB 2

Internet Architecture Principles Connectivity is its own reward • The value of a network increases in proportion to the square of the number of nodes on the network (Robert Metcalf's law) • Be liberal with what you receive, conservative with what by Jon Postel you send – try to make your best to understand what you receive – maximum adherance to standard when sending • Snowballing effect keeps all interested in connectivity thus keeps adhering to standards Internet-6 S-38.2121 / Fall-06 / RKa, NB Routing is divided into interior and exterior exterior neighbors border router - at least one neighbor Autonomous System (AS) belongs to another = networks operated by autonomous system a single organization interior neighbors and having a common routing strategy In this course we only deal with interior routing Internet-7 S-38.2121 / Fall-06 / RKa, NB 3

Routing is divided into interior and exterior • Interior routing protocols – Routing Information Protocol (RIP), RIP-2 – Open Shortest Path First (OSPF) – Interior Gateway Routing Protocol (IGRP), EIGRP – Intermediate System-to-Intermediate System (IS-IS) • Exterior routing protocols – External Gateway Protocol (EGP) (historical) – Border Gateway Protocol version 4 (BGP-4) Internet-8 S-38.2121 / Fall-06 / RKa, NB By connecting Ethernet segments with routers the traffic of the segments can be separated Host 1 Host 3 Ethernet 1 Bridge Router Host 2 does not receive Ethernet 2 ATM packets sent by Host 1 to other hosts on Ethernet 1 A router Host 2 • operates on the network layer • can interconnect networks of different technology Internet-9 S-38.2121 / Fall-06 / RKa, NB 4

Two functions of a router: 1. Packet forwarding Which is the following On which interface should destination on that network? this packet be forwarded? Host 3 address C address F address D Router address E address B address A Host 2 Look in the routing table! Host 1 Internet-10 S-38.2121 / Fall-06 / RKa, NB Two functions of a router: 2. Construction and maintenance of the routing table • Routers exchange routing information with routing protocols (e.g. RIP, OSPF, BGP) Router Router Router Internet-11 S-38.2121 / Fall-06 / RKa, NB 5

Internet routing is based on routing protocols, which collect information • Routing is completely automatic • No offline route planning • Only dimensioning is made offline • The routers communicate with a routing protocol • The routing algorithm finds the shortest (cheapest) route to every destination Internet-12 S-38.2121 / Fall-06 / RKa, NB Routing in the Internet is generally dynamic, but static routing is used in some cases • Dynamic routing is based on routing protocols which create and maintain the routing tables automatically – examples of routing protocols are RIP, OSPF, BGP... – E.g. to connect an organization with multiple links to the Internet • Static routing is based on manually configured routing tables. – Static routing is used when e.g. two peer providers do not trust each other – To connect an organization to a service provider with a single connection – Static routing is difficult to maintain Internet-13 S-38.2121 / Fall-06 / RKa, NB 6

The IP address defines the interface (not the host) Host 3 IP address C IP address F Router IP address D IP address E IP address B IP address A Host 2 Host 1 Internet-14 S-38.2121 / Fall-06 / RKa, NB Every interface also has a media specific MAC address Host 3 IP address C IP address F MAC c MAC f Router IP address D IP address E IP address B MAC d MAC e MAC b IP address A MAC a Host 2 Host 1 Internet-15 S-38.2121 / Fall-06 / RKa, NB 7

Internet layer model – hosts and routers Host 1 Router Host 2 Application Application TCP/ TCP/ UDP UDP IP IP IP MAC MAC MAC Network 1 Network 2 Internet-16 S-38.2121 / Fall-06 / RKa, NB Layers and message forwarding Application Application IP address C MAC c Router TCP/UDP Router TCP/UDP IP address D IP address B MAC d MAC b IP A B IP C D IP IP address A Host 2 MAC a a b c d MAC MAC MAC Host 1 network 1 network 2 Encapsulation: a b, IP A D, TCP TCP header Data Ethernet header IP header Encapsulation: c d, IP A D, TCP TCP header Data Ethernet header IP header Internet-17 S-38.2121 / Fall-06 / RKa, NB 8

IPv4 address formats • Originally a two-level (network, host) hierarchy 32 bits 1981 Class MSB Network Host A 0 7 bits 24 bits B 10 14 bits 16 bits C 110 21 bits 8 bits D 1110 28 bits - multicast address E 1111 For experimental and future use Internet-18 S-38.2121 / Fall-06 / RKa, NB IPv4 address formats 1984 • A new level for easier network administration Network Subnet Host Example: Address: 10.38.154.117 00001010 00100110 10011010 01110101 Mask: 255.255.192.0 11111111 11111100 00000000 00000000 Network: first bit “0” 00001010 = 10 Subnet: address* AND mask 001001 = 9 (36) Host: address AND NOT mask 10 10011010 01110101 = 2.154.117 address* = address with network part zeroed Also written as 10.38.154.117/14 Internet-19 S-38.2121 / Fall-06 / RKa, NB 9

IPv4 address formats • Examples: Mask IP address Network Subnet Host Mask IP address Network Subnet Host 0xFFFF0000 10.27.32.100 A: 10 27 32.100 0xFFFFFE00 136.27.33.100 B: 136.27 16 (32) 1.100 136.27.34.141 136.27 17 (34) 0.141 0xFFFFFFC0 193.27.32.197 C: 193.27.32 3 (192) 5 High order bits: Without right zeroes (and with right zeroes) 0 ..... 0 - 127. ÿ A-class 10.... 128. - 191. ÿ B-class R I D C y d b e a t p d u e r 110...192. - 223. ÿ C-class a t L ) e r a t d l s e u s s c d i ( Internet-20 S-38.2121 / Fall-06 / RKa, NB Routers maintain routes to networks (not to hosts) • Example Host 3 Network 10.29.0.0 / 16 10.29.0.1 10.30.0.2 Network 10.30.0.0 / 16 Router 10.30.0.254 10.30.0.1 10.31.0.30 Network 10.31.0.0 / 16 10.31.0.35 Host 2 Host 1 Internet-21 S-38.2121 / Fall-06 / RKa, NB 10

Aggregation describes several addresses in a single entry to reduce size of routing tables • Example Host 3 Network 10.29.0.0 / 16 10.29.0.1 10.30.0.2 Network 10.30.0.0 / 16 Network 10.30.0.0 / 16 Router 10.30.0.254 10.30.0.1 10.31.0.30 Network 10.31.0.0 / 16 10.31.0.35 Host 2 Host 1 Network 10.0.0.0 / 8 Internet-22 S-38.2121 / Fall-06 / RKa, NB Special purpose addresses • An unknown network is replaced by 0 – Only used as source address (e.g. a booting host) – 0.0.0.0 = ”this host in this network” – 0.X.Y.Z = ”host X.Y.Z in this network” • Limited broadcast address 255.255.255.255 – To all host in the local network • Directed broadcast addresses A.255.255.255, B.B.255.255, C.C.C.255 – To all hosts in a specified network • Loopback-address 127.X.X.X (usually 127.0.0.1) – Internal in one host • Multicast-addresses (e.g. 224.0.0.2 = all routers on this subnet) Internet-23 S-38.2121 / Fall-06 / RKa, NB 11