cs 3505 the internet and the info highway ip : internet protocol

CS 3505CS 3505 the internet and the info the internet and the info

highwayhighwayIP : internet protocolIP : internet protocol

IP topicsIP topics brief history

basic function

names and addresses

packet format

packet routing, routing tables

IPv6 : the IP of the future

Internet : historyInternet : history ARPAnet - 1st packet switched network,

1969 Larry Roberts - packet switching, ARPAnet BBN - built first IMPs 1970s - ARPAnet grew rapidly ethernet - PARC, Robert Metcalf 1970s token ring, IBM - 1970s TCP/IP - Vint Cerf - about 1980

IP : basic functionIP : basic function

provides connectionless, best-effort data delivery service to TCP/UDP/apps. Packet delivery not guaranteed.

Makes use of underlying networks (LANs/ WANs)

interface between transport layer (TCP,UDP) and the network interface (ethernet, token ring, FDDI, WAN)--> “workhorse” of Internet; “glue” that connects many networks

IP : basicsIP : basics

runs in routers (gateways, layer 3 switches) and hosts (end systems; computers).

routers are network switches which connect networks to other networks (and other routers). Mostly software. [AKA gateways]

transport layer (TCP,UDP) - run in hosts only, not in routers. Interface to IP.

TCP/IP internet TCP/IP internet

WAN

IP

WAN

IP

IP

IP ...TCP/IP

TCP/IP

TCP/IP

TCP/IP protocol suiteTCP/IP protocol suite

IP

TCP UDP

LAN/WAN

media

IGMPICMP

RARPARP

telnet, FTP, etc. TFTP, other apps.apps

IP : names and addressesIP : names and addresses

need unique name for every host

hierarchical naming structure

top level names assigned by InterNIC registration service

lower level names assigned by organization

ex: cs.nps.navy.mil

mil is the top level domain ; navy next level, nps next, etc.


some top level domains --edu - colleges & universitiesgov - US fed. gov’t agenciescom - commercial organizations in USnet - internet service organizationsorg - non profit institutionsmil - U S militarycountries --> jp, uk,fr, mx, de, etc.


name - series of labels, dots --bellcore.comwww.apple.comcs.nps.navy.mil

label can have up to 63 characters, and up to 255 characters in a name

worldwide naming tree -- root is top; domain is a node of the tree and its subtree

IP addressIP address

IP address : 32 bit number, assigned to each “host” (computer) on an IP internet.

switching nodes in the internet - routers - also must have IP addresses.

the IP address actually is assigned to interface point on the network, not the node itself .... analogous to street and house number for a home address


IP address - 2 main parts, netid and hostid

each part can be 1,2 or 3 bytes (class) first few bits indicate which class applies

Class A : netid 1 byte, host id 3 bytes Class B : 2 and 2 Class C : 1 and 3

netid hostid


dotted decimal notation --> 131.120.1.60 formats -> 0 (A), 10 (B), 11(C) ... in

decimal, if 1st byte : 0-127 --> A, 128-191 --> B, 192-223 --> C.

additional classes :D, 224-239, for multicastingE, 240-255, reserved.

some address blocks reserved for networks not connected to the Internet


how many possible IP addresses, total?

how many class A addresses exist? B? C?

how many hosts are possible for each class A? B? C?

is this an efficient method of assigning address classes in the Internet?


suppose your organization (eg, NPS) has a class B address; you don’t have 1 big network of 64K hosts; you have numerous smaller networks, mostly LANs.

further -- 64K is far too many hosts for a LAN or even a LAN internet, anyway....

how these be separated into smaller, more manageable networks?

IP addresses - subnetsIP addresses - subnets

the host space can be divided further into a subnet part and a host part (or system part).

example: NPS is 131.120.X.Y.... we can make X (3rd byte) the subnet id, and the rest (4th byte) the host id.

This gives room for ~255 subnets of up to 255 hosts each.... “131.120.1” is one of the CS dept subnets...

names and addresses : subnetsnames and addresses : subnets

131.120.1 131.120.10

131.120.5

131.120.20

NPS: 131.120


these different networks are connected by routers, and the NPS network is connected to the “outside” by a router.

how do the routers “know” which part is the subnet and hostid part?

--> subnet mask - a 32 bit string of bits; 1s correspond to the netid part (network and subnet), 0s to the system (host) part


some bit patterns are reserved for special purposes (e.g. broadcasting) , so ---

netid, hostid(subnetid) -- should not be all 0s or all 1s

netid, hostid(subnetid) -- must be at least 2 bits

IP addresses : multihomingIP addresses : multihoming

recall that IP address has 2 parts, the netid and hostid

routers, and sometimes hosts, may be connected to more than one network; which netid is the correct one?

--> both; the IP address corresponds to the network interface, not simply to the host itself. (think of a house on a corner....)

similarly, a host connected to 2 networks may be structured as a router

names and addressesnames and addresses

IP runs on top of ethernet LANs, TR LANs, etc. These rout packets according to a different address, the MAC address (not the IP address). How can IP rout packets on these networks?

--> must determine the MAC address which corresponds to a given IP address

ARP address resolution protocol

ARP :address resolution protocolARP :address resolution protocol

purpose : obtain MAC (hardware) address of a machine, given its IP address.

which MAC address has IP address 127.54.3.4?

IPMAC


IP frame “fits” into the frame of the underlying network... (“wrapper”)

IP frame

CSMA/CD frame

INFO

MAC DA,SA


input : IP address, i ;output : MAC address, m; data structure : ARP table: list of (i,m) pairs;

begin 1. search ARP table for i ;

if found, return (m) else broadcast ARP request (i );

2. wait for ARP reply (m); 3. when reply received, update ARP table (i,m)

& return (m). end


“broadcast request” - a LAN broadcast packet, contains the ARP packet (below)

2 2 1 1 2 6* 4 6* 4

src/dest MAC address

src/dest IP address

MAC hardware type

IP/upper layer type

lengthsARP msg type(request,reply)

(field lengths shown in bytes)

** ethernet length, may vary with

other protocols


receiver part of ARP : upon receipt of an ARP request,

if the destination IP address is MA (my address), then

1. update my ARP table, as appropriate, and

2. send ARP reply.

IP packet formatIP packet format

source IP address

destination IP address

options, (if any)

DATA

0 15 16 31

total length

identification

protocol header checksumTTL

fragment offset

vers. HLEN

flags

3 4 7 8 10

pre. TOS

IP packet - explanationIP packet - explanation

version -- currently 4; next - 6. HLEN - header length; 20 to 60 bytes. total length - packet length in bytes. precedence (3 bits) - designed for

priority, but no standard procedure for this; little used.

TOS - type of service TTL - time to live (die). Standard

specified seconds, but in practice - router hops.

IP packet - explanationIP packet - explanation

ID - numbers each datagram sent by a host. ( fragmentation/reassembly)

flags - 3 bits. DF, don’t fragment; MF, more fragments. (1st bit unused=0).

frag offset - ( fragmentation/reassembly)

protocol - indicates TCP, UDP, etc.

header checksum - done on header only; recomputed at each hop.

IP routing IP routing

routing mechanism - the mechanics of routing; simply, IP routs packets according to a routing table, in memory.

routing policy - how the paths in the networking are calculated- i.e., how the entries in the table are determined. Two separate procedures.

mechanism - differs slightly, depending on whether in a host or a router; simpler for hosts.

IP routingIP routing

basic IP routing mechanism:

given an IP DA (destination IP address),

1. search table for complete IP DA; if found, send to next hop indicated.

2. search table for network ID; if found, send to next hop indicated.

3. search for default entry; if found, send to next hop indicated.

4. discard the packet.

IP routing : in a host IP routing : in a host

IP (in host) receives packets to send from TCP, UDP, ICMP, IGMP.

upon receipt of a packet to send, IP will 1. check mask (determine net/host parts).

2. if destination directly connected (point-to-point link/ same subnet), then send packet to it.

3. otherwise, send packet to the default router (routing table).

IP routing : in a hostIP routing : in a host

fundamental difference : a host never forwards a packet; IP packets received not for this host are discarded.

note : if sending to a host on same subnet (e.g.

ethernet), the MAC address corresponds to the IP DA;

if sending to default router, the MAC/hardware DA is the router’s, while the IP DA is that of the final destination.

IP routing : in a hostIP routing : in a host

routing table

IP (host)

TCP, UDP, etc.

get next hop

NW interface

input queue

this IP DA or

broadcast packet?

yes

nobit bucket

IP routing : in routersIP routing : in routers

Same basic algorithm as stated, but :

routing tables bigger, generally ;

more overhead in maintaining routing tables, exchanging information with other routers;

more network interfaces, generally ; usually at least 2 (hosts may have only 1)

forward packets received onto other routers. (fundamental difference)

IP routing : in routersIP routing : in routers

routing table

IP (router)

TCP, UDP, etc.

get next hop

NW interfaces

input queue

this IP DA or

broadcast packet?

yes

no

IP routing tables IP routing tables

series of entries which contain

destination - IP address of distant location (either network or host)

gateway(router) - IP address of router to send the packet to

flags - 5 of these which give additional info

refcnt - number of active uses

use - number of packets sent this route

interface - the outgoing interface for this route; (e.g., ethernet, a direct link, etc. )

IP routing IP routing

routing mechanism - the mechanics of routing -- discussed previously

routing policy - how the paths in the network are calculated-- there is no single required routing policy on the Internet-- DV and LS routing already discussed

-- some specific IP policies to follow

IP routing mechanism (review)IP routing mechanism (review)

given an IP DA (destination IP address),

1. search table for complete IP DA; if found, send to next hop indicated.

2. search table for network ID; if found, send to next hop indicated.

3. search for default entry; if found, send to next hop indicated.

4. discard the packet.

autonomous systemsautonomous systems

a piece of the Internet unified by a routing policy

“somebody’s network” early def: a collection of subnetworks and

hosts, interconnected by routes

new def: a connected group of 1 or more IP prefixes ... which has a SINGLE and CLEARLY DEFINED routing policy

autonomous systemsautonomous systems

routing within ASs is done by IGPs, or interior gateway protocols; chosen by the controlling organization

routing between ASs is done by EGPs, or exterior gateway protocols

AS

AS

ASRIPIGRP

EIGRP

EGP

OSPF : open shortest path firstOSPF : open shortest path first

link state protocol, developed by IETF; non proprietary

low overhead; updates report changes rather than everything

quick detection of topology changes, rapid updating after changes

traffic splitting over multiple paths subnet masks supported authentication supported widely used, refinements will continue

cs 3505 the internet and the info highway ip : internet protocol

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