cs4550 computer networks ii ip : internet protocol, part 1: history, basic function, names and...
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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
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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)
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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
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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
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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.
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TCP/IP internet TCP/IP internet
WAN
IP
WAN
IP
IP
IP ...TCP/IP
TCP/IP
TCP/IP
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TCP/IP protocol suiteTCP/IP protocol suite
IP
TCP UDP
LAN/WAN
media
IGMPICMP
RARPARP
telnet, FTP, etc. TFTP, other apps.apps
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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.
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IP : names and addressesIP : names and addresses
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.
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IP : names and addressesIP : names and addresses
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
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IP : names and addressesIP : names and addresses
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
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IP : names and addressesIP : names and addresses
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
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IP : names and addressesIP : names and addresses
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
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IP : names and addressesIP : names and addresses
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?
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IP : names and addressesIP : names and addresses
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?
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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...
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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
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names and addresses : subnetsnames and addresses : subnets
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
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names and addresses : subnetsnames and addresses : subnets
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
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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
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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
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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
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ARP :address resolution protocolARP :address resolution protocol
IP frame “fits” into the frame of the underlying network... (“wrapper”)
IP frame
CSMA/CD frame
INFO
MAC DA,SA
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ARP :address resolution protocolARP :address resolution protocol
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
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ARP :address resolution protocolARP :address resolution protocol
“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
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ARP :address resolution protocolARP :address resolution protocol
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.
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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.