Transcript Protocols & the TCP/IP Suite

Chapter 3 – Protocols & the TCP/IP
Suite
Class 1
1
Protocols & the TCP/IP Suite
The Need for a Protocol Architecture
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Communication between a set of networked systems can
involve a very complex set of procedures
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Example tasks for file transfer:
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Communication link setup
Ensure the receiver is ready to accept data
Make sure the file management application at the receiver
is prepared to receive and store the file
Do file translation if necessary
Confirm delivery & check for errors
Networking protocols use the concept of modularity well
known in the software development arena
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Protocols & the TCP/IP Suite
The Need for a Protocol Architecture
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In Networking protocol architectures, the modules are
arranged in a vertical stack
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Each layer performs a distinct & essential set of tasks; more
‘primitive’ tasks are usually found in lower layers (‘closer’ to
the transmission medium)
Layers should be defined so changes in one layer do not
necessitate changes in the other layers
It takes at least two systems to communicate across a
network and each of these systems need the same layers
The peer layers on each system communicate with each
other; the set of rules governing it is known as a protocol
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Syntax
Semantics
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Timing
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Protocols & the TCP/IP Suite
The TCP/IP Protocol Architecture
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The TCP/IP protocol suite is a large collection of public
standards approved by the IAB (IETF) and used as the
foundation for the Internet and similar private networks
Communication across a network using TCP/IP protocols
involves two general steps:
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Getting the data across the network to the destination systems
Getting the data within the destination system to the right
application
Because of layering & the general steps above, the TCP/IP
protocol suite was designed with five layers (lowest to
highest):
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Physical Layer: the physical interface between the network and
the attached system; covers the nature of the data signals,
characteristics of the transmission medium, the data rate, etc.
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Protocols & the TCP/IP Suite
The TCP/IP Layers
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Network Access Layer: specifies how data is exchanged
between the attached system and the network; will include
addressing, framing, and other features such as
prioritization
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Details of this layer depends on the physical layer; separating
this layer from higher layer functions allows higher layers to
be used over a wide range of network technologies
Concerned with delivering data across a single network only
Internet Layer: specifies how data can be routed across
multiple networks
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All devices across an internet must share a common
internetworking layer to relay the data
Routers are the devices responsible for relaying data in an
internet
A global address space is an essential feature of this layer
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Protocols & the TCP/IP Suite
The TCP/IP Layers
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Transport Layer: specifies a set of end-to-end services
usually common to a number of applications
communicating across an internet (error-free, sequenced
data delivery, etc.)
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Currently there are two transport layer specifications in the
TCP/IP suite: the Transmission Control Protocol (TCP) and
the User Datagram Protocol (UDP)
TCP provides a reliable connection-oriented transport service
UDP provides a low overhead transport service with no
payload error checking, flow control, or sequencing
Application Layer: specifies the functionality of the
application itself (file transfer, remote terminal access,
etc.)
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Protocols & the TCP/IP Suite
The Operation of TCP & IP
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For successful communication across an internet, each
system must have at least one globally unique address
Also, each host process needs a locally unique address
An example TCP/IP based data transfer [Figure 3.1]
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Protocols & the TCP/IP Suite
The Operation of TCP & IP
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The key to operation of the protocol stack is encapsulation
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Protocols & the TCP/IP Suite
Examples of TCP/IP Applications
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Electronic Mail relies on the Simple Mail Transfer Protocol
(SMTP) – this covers the addressing and delivery of messages;
other standards cover e-mail message format
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File Transfer functionality relies on the File Transfer Protocol
(FTP), which provides an authenticated means for accessing and
transferring files to and from a remote system
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Remote Terminal Access functionality relies on the TELNET
protocol; it emulates a variety a hardwired terminals over a
network connection
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Other important TCP/IP Applications include the World Wide
Web (HTTP or the Hypertext Transfer Protocol), Network News
(NNTP or the Network News Transfer Protocol), and Directory
Services (LDAP or the Lightweight Directory Access Protocol)
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•NV Monitoring of UDP Ports for Applications (NetView to monitor the different UDP ports for applications)
•TFTP Trivial File Transfer Protocol, a simple form of ftp, with most of the security and advanced commands stripped off, used
for diskless workstations, router configuration data, and any device that boots up, and requires information it cannot store
permanently. As such it presents a rather large security hole, just imagine if someone were to connect to your tftp server and grab
the boot file for your main Cisco router.
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Protocols & the TCP/IP Suite
The OSI Protocol Architecture
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The ISO (an international standards body) has also
developed a network protocol reference standard called
the OSI model
While useful to know and important in the context of
some international networks, the OSI model has not
flourished for two primary reasons:
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The TCP/IP have matured and equipment using these
protocols were widely adopted before the OSI model was
finished
The OSI model and standards developed using it tend to be
very complex, making them harder to implement and
operate
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Protocols & the TCP/IP Suite
The OSI Protocol Architecture
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The OSI model consists of seven layers (from bottom up):
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Physical: concerned with the transmission and signaling across
the physical media (same as TCP/IP model)
Data Link: provides reliable transfer on a physical link by
formatting data in frames; providing timing, error, & flow control
Network: provides a universal switching/routing layer to insulate
upper layers from differing data link & physical layers
Transport: provides reliable, transparent end-to-end delivery of
data; may also provide end-to-end error recovery & flow control
Session: establishes, manages, and terminates connections
between communicating applications
Presentation: specifies how data should be represented between
communicating applications
Application: provides user access to networked resources
through a specific functional program
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Protocols & the TCP/IP Suite
Internetworking
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It is very common for an organization to have different
varieties of LANs as well as geographically dispersed
networks
A quick review of Internetworking Terms
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Communication Network
Internet (internet)
Intranet
End System
Intermediate System
Bridge
Router
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Protocols & the TCP/IP Suite
Routers
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Routers are key pieces of equipment that allow
internetworking across dissimilar networks
Essential functions for a router:
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Provide links between physically distinct (and heterogeneous)
networks
Decide when and where to forward packets to attached
networks
Provide these functions in such a way that no modifications
are required to the attached networks
Networking issues routers must deal with:
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Layer 2 Addressing Schemes
Maximum Packet sizes
Interfaces
Reliability
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Protocols & the TCP/IP Suite
An Internetworking Example [Figure 3.5]
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Overall Path for Outgoing Packets
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Overall Path for Incoming Packets
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Protocols & the TCP/IP Suite
Appendix: IP, TCP, and UDP
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IP version 4 (IPv4)
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The current version of the network
layer protocol used in the Internet
IPv4 header fields:
Version (4 bit) currently 4
Internet Header length (4 bits)
0101x 32 bits
Type of service (8 bits): priority
infor. to routers
Total length (16 bits) IP packet in
byte
Indentification (16 bits) unique
identifier
Flags (3 bits): (1) “more bit” for
fragments, (2) “don’t fragment”,
(3) not used.
Fragment offset (13 bits) offset in
original packet of this packet.
Time to live (8 bits) life time in
Internet
Protocol (8 bits): indicates next
higher level protocol to receive
packet
Header checksum (16 bits) error
detection done by routers
Source address and Destination (32
bits) specifies network and end
system.
Option: security, record routing,
and time-stamping.
Padding: ensure header is multiple
of 32 bit.
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Protocols & the TCP/IP Suite
Appendix: IP version 6 (IPv6)
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Next generation version promises a number of improvements:
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HUGE address space, with support for a many addressing schemes
Different header structure and options to speed processing
Built-in Quality of Service and security functionality
IPv6 Header fields:
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Protocols & the TCP/IP Suite
Appendix: the Transmission Control
Protocol (TCP)
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Provides a sophisticated connection-oriented transport
service to networked applications on an IP network
TCP provides reliable and sequenced streaming delivery of
application-layer data
TCP Header fields:
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Protocols & the TCP/IP Suite
Appendix: the User Datagram Protocol
(UDP)
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Provides a basic low-overhead connectionless transport
service to networked applications on an IP network
UDP provides unreliable delivery of application-layer data
in which delivery or duplication of data is not guaranteed
UDP is good for applications that provide their own
enhanced delivery services as well as multicast and
streaming applications
UDP Header fields:
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Memory-Memory Copies
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Protocol processing overhead:
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Example: delay due to memory-memory copy
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Copy message from one layer to the next using e.g., memcpy()
Often involves context switching: copying between user and kernel
space
Assume Data rate of 600Mbps=73MBps
Assume 16MHz memory bus that is 16 bits wide  32MBps
For a 1 MB message, one copy takes 1/32 sec  max data rate
32MBps
Two copies take 1/32 sec + 1/32 sec = 1/16 sec  max data rate
16MBps
Example: effective BW
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Itanium 4 bus allows 1 GB/s bandwidth
Each copy between layers takes a read and a write
A message of 1 KB takes 2 msec  effective BW = 500 MB/s
Two copies of 1 KB takes 4 msec  effective BW = 250 MB/s
Four copies of 1 KB takes 8 msec  effective BW = 125 MB/s
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Berkeley Sockets
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A real implementation of transport layer primitives
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Implemented in BSD Unix
Part of TCP implementation in TCP/IP stack
Socket primitives for TCP
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SOCKET: Creates new communication end point
BIND:
Attaches a local address to a socket
LISTEN: Announce willingness to accept connections
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ACCEPT:
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non-blocking call
Blocks the caller until a connection attempt arrives
Blocking call
Server creates a new socket when connection request TPDU arrives and
forks another process to handle subsequent requests
CONNECT: Establishes a connection
SEND:
Send data over the connection
RECEIVE: Receive data from the connection
CLOSE:
Release connection
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BSD Sockets Example: Receiver Side
/* Simple socket program: receiver side
#include <iostream.h>
#include <stdlib.h>
#include <stdio.h>
#include <stream.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <sys/time.h>
*/
void main ( int argc, char *argv[] )
{
int sk ;
// socket descriptor
sockaddr_in remote ;
// socket address for remote
sockaddr_in local ;
// socket address for us
char buf[80] ; // buffer from remote
int rlen = sizeof(remote);// length of remote address
int len = sizeof(local); // length of local address
int mesglen ; // actual length of message
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// create the socket
sk = socket(AF_INET,SOCK_DGRAM,0) ;
// set up the socket
local.sin_family = AF_INET ;
// internet family
local.sin_addr.s_addr =
INADDR_ANY ; // wild card machine address
local.sin_port = 0;
// let system choose the port
// bind the name (address) to a port
bind(sk,(struct sockaddr *)&local,sizeof(local)) ;
// get the port name and print it out
getsockname(sk,(struct sockaddr *)&local,&len) ;
cout << "socket has port " << local.sin_port << "\n" ;
mesglen = recvfrom(sk,buf,80,0,(struct sockaddr *)&remote,&rlen);
cout << buf << " len: " << mesglen << endl;
/* close the socket */
close(sk);
}
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BSD Sockets Example: Sender Side
/* A simple sockets program ... sender side */
#include <iostream.h>
#include <stdio.h>
#include <stream.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ipc.h>
#include <sys/time.h>
void main ( int argc, char *argv[] )
{
int
sockaddr_in
side
hostent
int
message
sk ;
remote ;
// socket descriptor
// socket address
*hp ;
// address of remote
mesglen ; // actual length of
// for remote
// host
// the
char buf[80];
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BSD Sockets Example: Sender Side
// create the socket
sk = socket(AF_INET,SOCK_DGRAM,0) ;
// designate the addressing family
remote.sin_family = AF_INET ;
// get the address of the remote host and store
hp = gethostbyname(argv[1]) ;
memcpy(&remote.sin_addr,hp->h_addr,hp->h_length) ;
// get the port used on the remote side and store
remote.sin_port = atoi(argv[2]) ;
cout << "Enter the info to transmit: ";
cin.getline( buf, 80);
mesglen = strlen(buf)+ 1;
cout << buf << " len: " << mesglen << endl;
sendto(sk,buf,mesglen,0,(struct sockaddr *)&remote, sizeof(remote)) ;
close(sk);
}
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BSD Sockets Example
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Compile and execute the two programs
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Save these programs on a Unix machine as recv.cc and send.cc
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Compile and link them:
E.g., on a Solaris workstation use:
gcc –o recv recv.cc –lsocket –lnsl and
gcc –o send send.cc –lsocket –lnsl
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You’ll get two executables: recv and send
Execute them on two different workstations:
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E.g., recv on one workstation and send on another using rlogin to that
workstation
Try the connection-oriented case now
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Use SOCK_STREAM instead of SOCK_DGRAM in socket() call
Use listen() and accept() calls
Also try spawning a new receiver after accept() to handle multiple
clients
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Network supports process-to-process channels; e.g.,
Latency = Propagation + Transmit +
Queue
Propagation = Distance / SpeedOfLight
3.0 x 108 meters/second in a vacuum
2.3 x 108 meters/second in a cable
2.0 x 108 meters/second in a fiber
Transmit = Size / Bandwidth
Request/Reply: for file access and digital libraries
• Message Stream: for video applications
– video: sequence of frames
– resolution:1/4 TV-size image = 352 x 240 pixels;
– 24-bit color: frame=(352 x 240 x 24)/8 =
247.5KB;
– frame rate: 30 fps = 7500KBps = 60Mbps
– video on-demand versus video-conferencing
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DNS
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Hierarchical.
Dot used as a separator.
Right-most component is the top-most domain.
Top-level domains: .edu, .gov, .mil, .com, .arpa, .org,
.net, plus the country domains (.uk, .de, .no, .il, etc...),
and the.us hierarchy.
New TLDs include .info, .biz, .name, …
FQDN: frobozzica.merit.edu vs. relative name frobozzica
(relative to a default domain, in this case merit.edu).
The reverse mapping from IP addresses to host names is
performed under the auspices of the IN-ADDR.ARPA
pseudo-domain.
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100.61.108.198.IN-ADDR.ARPA
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DNS - Resolver
DNS - Resolver
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The DNS resolver (client library) generates queries for domain name
information sent to a name server.
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Completely separate from the name server function.
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Configured via /etc/resolv.conf
domain merit.edu
search org.merit.edu, itss.umich.edu
nameserver 127.0.0.1
nameserver 198.108.1.42
DNS - Server
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Answers DNS queries sent by resolvers.
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Listens at UDP and TCP port 53
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UDP used for routine queries
TCP used for zone transfers
A zone is part of the name space (merit.edu) delegated to a single
server.
A domain is also part of the name space, but it may cover several zones
(e.g., umich.edu covers engin.umich.edu, eecs.umich.edu).
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DNS - Server
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Configurations
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Caching-only: relies on other name servers for authoritative
answers
Primary: Contains the writeable authoritative copy for the
zones that it is primary for
Secondary: Contains a mirror copy of the data from a
primary name server. No updates take place here; used to
provide redundancy
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DNS - Operation
what is the IP address
of www.merit.edu?
local DNS sends query
to DNS @ merit.edu,
www.merit.edu?
local DNS sends query
to root DNS server
DNS @ merit.edu returns IP
address of www.merit.edu
198.108.1.48 to local DNS
root DNS server returns
IP address of
DNS server at merit.edu
local DNS returns answer to
resolver, www.merit.edu is
198.108.1.48
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Distributed Switching and Routing Architecture
Control
Module
Slot 1
Main Memory
10BseT
DUART
R5000
Line
Card
Slot 2
Flash
Card
EE
Prom
Line
Card
Slot 3
Line
Card
Slot 4
PHY
PHY
PHY
L2
L2
L2
L3
L3
L3
Switching Fabric
L3
L3
L3
L3
L2
L2
L2
L2
PHY
PHY
PHY
PHY
Slot 5
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Card
Slot 6
Line
Card
Slot 7
Line
Card
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Slot 8
Line
Card
Distributed Input/Output Processing
Input Processing
L2 Database
L3/L4 Database
Priority
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Encaps & Queuing
Accounting Filters
Accounting
Crossbar
Filters
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Demux
Priority
Arbiter
Bridge
or
Route
Output Processing
Encaps
QoS
Flow & Table Management
CPU Module
First
Packet
Bridging
VLANs
Routing
Access
Control
QoS
Policy
RMON/
RMON2
Input Processing
L2 Database
Output Processing
Priority
Accounting
L3/L4 Database
Priority
Accounting
Encaps & Queuing
Filters
Crossbar
Demux
Bridge
or
Route
Arbiter
Subsequent
Packets
Encaps
QoS
Filters
Flow classification and distribution is better than 25,000 flows per second
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Crossbar
 2.0 Gbps per channel (SSR8000/8600)
 4 priority queues per input and output channel
 Packet switching
 Overspeed
 Overflow at output buffers
 Avoid Head Of Line - look 4 deep per queue
 Multicast packets replicated in hardware
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Multicast Support
Switch Fabric
Output
Module
Input
Module
Output
Module
QoS ensures priority
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Output
Module
Standards based Multicast support
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IGMP v2 (seamless integration
with workstations/servers)
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DVMRP v3
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PIM-DM, PIM-SM
Efficient packet
replication via switch
fabric
Expanding Ring
TTL Support
ACLs screen out hosts which
attempt to join certain multicast
groups
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QoS - Packet Classification
(Four Classes of Service)
Switch Fabric
ASIC based Layer-3/4
Packet Classifier
Line Speed Gigabit Input Streams
Buffer Queues
Control Priority
Layer-3: Layer-4 flows mapped to CoS
High Priority
Layer-2: 802.1p priority mapped to CoS
Medium Priority
Low Priority
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QoS - Multiple Prioritization Schemes
Dual MAC
Buffer Queues
Switch Fabric
Weighted Fair Queuing (ex. 25% per queue)
ASIC based Packet
Encapsulating Engine
Line Speed 100 Mbps Streams
Buffer Queues
Strict Priority Queuing
Control Priority
High Priority
Layer-3: TOS/DiffServ Packet Marking
Medium Priority
Layer-2: 802.1p Packet Marking
Low Priority
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Per Flow Committed Access Rate (CAR)
(Rate Limiting)
Excess bandwidth discarded
Buffer Queues
HTTP Flow
H
H
e
FTP Flow
F
H
H
F
eMail Flow
HTTP Flow
H
H
F
e
H
H
FTP Flow
F
H
H
H
F
H H H H H H
ASIC Layer-3/4
Packet Classifier
F
H
Switch Fabric
F F F
e
Buffer Queues
H H H H H H
F F F
eMail Flow
H e
CAR can be performed on
- per port
- per flow(s)
- per application(s)
- per host(s)
in kilobits per second
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Excess Bandwidth reprioritized
to a lower priority
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Control Priority
High Priority
Medium Priority
Low Priority
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Random Early Detection (RED)
Drop All
Queue Depth
Avg. Queue
Depth
Drop Probability
Maximum
Threshold
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Maximizes throughput under congestive
conditions
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Provides fair bandwidth reduction
between host connections thru implicit
notification (dropped packets)
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Works for TCP only, use CAR for UDP
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Intelligently differentiates between
transient bursts and excessive offered
load
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Avoids TCP slow start oscillations
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Reduces overall nodal latency
Minimum
Threshold
Time
Weighted RED (WRED) is RED policies per Queue
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Key Redundancy Features
Fully hot swappable with redundant
Control Modules and Switch Fabrics
5509
Aggregate links with SmartTRUNK
Fully Interoperable with Cisco’s Fast
Etherchannel and other Server trunking
protocols
Any number of links can be aggregated
(ex. 7 Gig Ethernet links = 14 Gbps BW)
Mix and match link speeds for
incremental bandwidth
Superior balancing based on flows rather
than MAC address
Can balance flows using “round robin” or
link utilization algorithms
VRRP
Standby
Router
VRRP (Virtual Router Redundancy
Protocol) protects clients using default
gateways
Equal Cost Multipath OSPF can multiply
the effective bandwidth over 4 paths
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Web Hosting with Gigabit Ethernet
Server Array Load-balancing based on
Layer 4 Application traffic: round robin,
server utilization, server availability
Transparent Web Caching: Redirect
HTTP requests to a Web cache server
Jumbo Frame Support with hardware
IP Fragmentation support to lower
MTU interfaces (“Don’t Fragment” bit
not set)
Large Packet Buffering to insure zero
packet loss under any conditions
Add a F5 Labs BIGip Server Array
controller for added load balancing
functionality
Layer-4 Quality of Service and Access
Control Lists plus support for Diff-serv
Full RMON I & RMON II Supported
along with LFAP for Accounting
635.412 Spring 2005
Class 1: Introduction to LANs & WANs
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