cs4550 computer networks ii ip : internet protocol, part 1: history, basic function, names and...

CS4550 CS4550 Computer Networks IIComputer Networks II

IP : internet protocol,IP : internet protocol,part 1: history, basic function, part 1: history, basic function,

names and addresses, ARPnames and addresses, ARP

read Feit chapter 5 to 8read Feit chapter 5 to 8

IP topicsIP topics brief history (1)

basic function (1)

names and addresses (1)

packet format (2)

packet routing, routing tables (2)

lnternet Control Message Protocol (2)

routing (calculation) : RIP, OSPF (2)

IPv6 : the IP of the future (2)

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 ref: Where wizards stay up late, Hafner

and Lyon, Simon & Shuster

IP : basic functionIP : basic function

provides a connectionless, best-effort data delivery service to transport layer or applications. Packet delivery not guaranteed.

Makes use of underlying networks technologies (LANs, WANs).

interfaces between transport layer (TCP,UDP,etc.) and the network interface (ethernet, token ring, FDDI, WAN)--> IP is the “workhorse” of the Internet; the “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. (generally software). [aka gateways]

transport layer (TCP,UDP) - run in hosts only, not in routers. Interfaces 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 used

top level names assigned by InterNIC registration service (Herndon, VA)

lower level names assigned by organizations

ex: cs.nps.navy.mil

mil is the top level domain, assigned by InterNIC ; 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.comtaurus.cs.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 address : a 32 bit number, which is 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 the 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 : 3 and 1

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 net 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 -- 65,000 is far too many hosts for a LAN or even a LAN internet, anyway....

how these be separated into smaller, more manageable networks?

IP : names and addresses --IP : names and addresses --subnetssubnets

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

Divided into 4 LANS with

Subnet mask

255.255.255.192


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

IP AND SUBNETMASK = subnet address


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

127.0.0.1 loopback255.255.255.255 broadcast on local

LAN

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

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

names and addresses : names and addresses : multihomingmultihoming

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.

Comments on ARP,Reverse ARP Comments on ARP,Reverse ARP (RARP) (RARP)

ARP - most systems allow system administrator to view table, make manual entries, or update table from file

Try : arp -a command from a school terminal

RARP purpose : to find out ones own IP address, from

the MAC address. Similar procedure. useful for diskless workstations, however --

now being replaced by BOOTP and/or DHCP (dynamic host configuration protocol). These provide more info than RARP.

cs4550 computer networks ii ip : internet protocol, part 1: history, basic function, names and...

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