Local Internets

1
Local Internets
Cabletron SmartSwitch 2100
2
Local Internets

• Internet
• System of subnets such that any station on any
  subnet can communicate with any station on any
  other subnet by placing the receivers address in
  a message
• Subnets are individual networks in an internet

3
Local Internets
LAN
LAN
LAN
LAN

• Local Internets
• Links multiple LANs at a single site
• Entirely on customer premises
• Planned and managed by the owner
• Company has no limits
• Company has all the headaches
• High-speed transmission (roughly LAN speeds)

4
Why a Local Internet?

• Overcome distance limitations
• 10Base-T networks span only 500 meters
• Overcome congestion and latency
• Individual shared media networks running around
  10 Mbps become saturated at 200-300 stations.
• Connect dissimilar LANs
• Link Ethernet and Token-Ring Network LANs

5
Local Internetting to Increase Distance Spans
Internetting Device
10Base-T LAN in Headquarters Building (500 m
maximum distance)
HQ LAN
Transmission Link (no max distance)
Internetting Device
10Base-T LAN in Factory Building (500 m maximum
distance)
Factory LAN
6
A Congested Shared Media LAN
Before Single LAN
Department 1 150 Stations
Department 2 150 Stations
A
B
C
D
Stations
Stations
All stations in Department 2 hear the message
B transmits to A
Each station hears the traffic of 300
stations Heavily congested.
7
Internetting keep most traffic within LANs
After Resegmentation
Department 1 150 Stations
Department 2 150 Stations
Internetting Device
A
B
C
D
Stations
Stations
Internetting Device Blocks the Transmission of
this message to Department 2
B transmits to A
Traffic of 150 stations Not Congested
Traffic of 150 stations Not Congested
8
Internetting Devices Bridges

• Simple, automatic, inexpensive, fast
• Usually only two ports
• A fast, cost-effective choice for small internets
• See CISCO whitepaper for more details

9
Multiple Bridges
LAN 2
X
LAN 3
LAN 1
LAN 4
No Loops Allowed Problematic for large bridged
internets
LAN 5
10
Multiple Bridges
Route Between LANs 1, 5
LAN 2
LAN 3
X
LAN 1
No loops means only one path between LANs No
alternative routing if failures, congestion No
way to optimize routing for security, etc.
LAN 5
11
802.1 Spanning Tree Standard
Route Between LANs 1, 5
LAN 2
LAN 3
Backup Link
LAN 1
Allows backup links Disabled during normal
operation If a failure occurs, automatically
initiated
LAN 5
12
Bridging LANs with Different Physical and MAC
Layers
Bridge
802.5 Token-Ring Network
802.3 10Base-T Ethernet LAN
Hub
10Base-T Connection
802.5 Connection
13
Bridging LANs with Different Physical and MAC
Layers
802.2 LLC Standard
LLC Layer (Same)
802.2 LLC Standard
802.1 Bridging Standard
802.1 Bridging Standard
Bridging Layer (Same)
802.5 MAC Layer (Token-Passing)
802.3 MAC Layer (CSMA/CD)
MAC Layer (Different)
802.5 Connection to Access Unit
Physical Layer (Different)
10Base-T Connection to Hub
14
Problems of Bridges

• Do Not Stop Broadcast Messages
• Servers broadcast their existence about twice a
  minute
• In contrast to normal messages, which are
  designed to go to single stations, broadcast
  messages go to all stations.
• Goes to all stations on the network bridges pass
  these messages on
• Problematic in large bridged intranets

15
Problems of Bridges

• Do Not Stop Any Client from Logging into Any
  Server
• Poor security. Only password protection on
  servers
• Bad if servers hold grades in a university
• Bad for departmental servers holding key
  personnel or financial data in a firm

16
Switches Solve Bridge Problems

• Begin as Multiport Bridges
• Add broadcast reduction, security

17
Simple Switched Internet
Connection 1
LAN A
Connection 1
LAN C
No Waiting!
LAN B
Connection 2
Switches can carry messages between several pairs
of LANs simultaneously.
Connection 2
LAN D
18
Switched Internet with Multiple Switches
Switch A
Switch B
Switch C
Switch D
LAN 1
LAN 2
Switches are arranged in a hierarchy Only one
route between any two LANs No routing around
failure, congestion No optimization of routes
Route 1-B-A-C-2
19
Switch Hierarchy

• Switches can be arranged hierarchically
• Levels of Switches
• Desktop switches (only a few MAC addresses can be
  supported)
• Workgroup switches (MAC addresses for members of
  a department)
• Enterprise switches (large number of MAC
  addresses)

20
Virtual LANs Reduce Broadcasting

• Stations are Divided into Groups
• Called Virtual LANs (VLANs)
• Server, other broadcasts limited to VLANs
• Not to all stations on all ports

LAN A
LAN B
LAN C
LAN D
Server only broadcasts to its VLAN stations on
LAN A, LAN C
21
VLANs Add Security

• Only stations on the same VLAN as a server can
  reach it to log in

On VLAN 36
On VLAN 7
X
LAN A
LAN B
LAN C
LAN D
Client can only reach server if they are on the
same VLAN
22
Simple Local Internet Using Ethernet Switching
and 10Base-T
Ethernet Switch
10Base-T Hub
10Base-T Hub
10Base-T Hub
In a switched Ethernet internet Stations connect
to hubs. Hubs connect to switches.
LAN
LAN
23
Switched Internets

• The Move Toward Switched Networks
• All-switched LANs with stations connected to
  switches are still too expensive for most firms.
  Need a port for each station.
• Using switches as internetting devices is
  cost-effective today. Only hubs connect to
  switches. Only need a port for each hub
• As switching costs fall, companies can later move
  switching down to individual LANs by replacing
  hubs by switches. See CISCO white paper for
  details.

24
Routers

• Most sophisticated internetting devices
• Provide services for linking thousands of subnets
• Used in the worldwide Internet, also within firms
• Efficient for long-distance transmission
• Provide wide range of management services to give
  relatively automatic operation
• By far the most expensive internetting devices

25
Route

• End-to-End Connection

1
LAN A
LAN B
3
2
4
LAN D
LAN A - 1 - 3 - 5 - LAN D
5
26
Alternative Routes

• Multiple Ways to Get from LAN A to LAN D

1
LAN A
LAN B
3
2
4
A-1-3-5-D A-1-3-4-D A-2-5-D Etc.
LAN D
5
27
Advantages of Alternative Routing

• Routing Around Failures
• Failed switches, trunk lines connecting switches
• Routing Around Congestion
• More common than outright failures
• Route Optimization
• Least cost route
• Most reliable route
• Most secure route, etc.

28
Mixing Switches and Routers
Site A
LAN
LAN
Site B
Switch
LAN
Router
Switch
Router
LAN
Site C
Router
29
Distributed Backbone Network
LAN 1
LAN 2
FDDI Backbone Ring
Router
Router
Router
LAN 3
30
Backbone Network

• Network that Links Subnets
• Subnets take the place of stations
• Distributed Backbone
• Backbone runs past all stations
• If a single router (or other internetting device)
  fails, only that station is disconnected
• FDDI is popular because of its possible 200 km
  circumference, 100 Mbps speeds

31
Local Internet Using Collapsed Backbone
LAN A
LAN B
LAN C
Routers at LANs
Routers at LANs
Central Switch or Router
32
Collapsed Backbone

• Single point of maintenance
• Easy to maintain the network
• Single point of failure
• If the central device fails, serious problems
• Types of central devices
• Switches
• Routers

33
OSI Layers

• Layer 1 (Physical)
• Electrical signaling over a physical link
• Layer 2 (Data Link)
• Data framing and administration of communication
  over a single data link
• Point to point connection
• Shared media LAN with only one possible path
  between two station
• Layer 3 (Network)
• Routing across an internet with multiple
  alternative routes
• Or a subnet that offers alternative routes, but
  these rarely exist

34
Internetting Devices

• Hubs
• Layer 1 merely reflect bits back out
• Bridges, Switches
• Layer 2 Work with MAC addresses
• No alternative routing
• Routers
• Layer 3 routing across internet
• Only device with alternative routing

35
TCP/IP Internetting
TCP/IP
OSI
Application
Transport
Internet

• Subnet layer
• Links stations on same subnet
• Often IEEE LAN standards
• PPP for telephone connections
• TCP/IP specifies almost any subnet standard
• For LANs, etc., specifies OSI
• OSI further subdivides into Physical, Data Link

Subnet
Data Link
Physical
36
TCP/IP Internetting
Application
Transport
Internet
Subnet

• Internet layer
• Links stations across internets
• Main standard is the Internet Protocol (IP)
• Dominant protocol for routers

37
TCP/IP Internetting
Application
Transport
Internet
Subnet

• Transport layer
• Links computers, even if different platforms
• Main standards are Transmission Control Protocol
  (TCP) and User Datagram Protocol (UDP)
• Application layer
• Links application programs even if from different
  vendors
• Many standards, because many applications
• SMTP for e-mail HTTP for the WWW, etc.

38
Universal Addressing

• Each host has a unique IP Number
• 32-bit binary number
• Goes in the IP headers source and destination
  fields
• 10000000101010110001000100001101
• Impossible to remember

Destination
Source
4 Bytes
4 Bytes
IP Packet
39
Subnet Mask

• Problem IP numbers do not include subnetting
• Solution Create a second number a Subnet Mask
• Define which bits of the IP address refer to
  subnets vs. hosts on subnet
• Subnet mask is 32 bits long, in dot quad format
• See last meeting TCP/IP in NT for basic IP and
  Subnet Mask concepts.

40
Routers

• Routers also get IP addresses
• So packets can be sent to them for routing
• Has network ID of the network on which it sits
• Must be assigned a host ID
• Example 128.171.17.1

128.171.17.104
IP Packet for Delivery
Default Router
Another Router
128.171.17.1
41
Routers

• Subnets can have Multiple Routers
• There is usually a default router for packet
  delivery
• Default router is used if no router is specified
• Routers are sometimes called gateways in TCP/IP

IP Packet for Delivery
Default Router
Other Router
42
Routing Protocols
Routing Table
There are no master routers. Each router works
independently to do routing. This requires each
router to build a routing table that contains
information about the locations of other routers.
43
Routing Protocols
Routing Table
Routing protocols allow routers to
exchange information in their routing tables.
44
Peer Control Among Routers

• Routers Communicate Among Themselves
• To coordinate their actions without central
  control
• Share knowledge of network connectivity
• Common standards are RIP, OSPF, BGP

Router Coordination Message
45
Routing Protocols

• RIP - Router Information Protocol
• High overhead, but simple and OK for small
  networks
• OSPF - Open Shortest Path First
• Optimizes routing, but complex
• BGP - Border Gateway (Router) Protocol
• Used in Internet Backbone Routers
• Read Cisco whitepaper for more on routing

46
Autonomous Systems
RIP or OSPF
Autonomous Router
Organization can select any routing protocol to
synchronize its autonomous (internal) routers.
RIP and OSPF are common. Border routers that
linkautonomous systems normally use BPG.
RIP or OSPF
Border Router
BPG
Autonomous System
Border Router
47
Error Handling

• TCP/IP a comprehensive set of error handling
  processes
• The Internet Control Message Protocol (ICMP) is
  used to send error messages.
• Hosts, Routers send ICMP messages to one another
  if a problem occurs
• Host not found is a common ICMP error message.

ICMP Error Message
Host
Router
48
Internet Control Message Protocol (ICMP)
The Internet Control Message Protocol (ICMP) is
for delivering supervisory messages among hosts
and routers
49
Internet Control Message Protocol (ICMP)
Host Unreachable
Error Messages
50
Internet Control Message Protocol (ICMP)
Flow Control Source Quench tells host to
reduce transmission rate.
Source Quench
51
Internet Control Message Protocol (ICMP)
Source host can ask questions of destination
hosts. Echo Request asks if the other host is
reachable. Destination host sends back Echo
Response. Usually implemented with
Ping program.
Echo Request
Echo Response
52
Autoconfiguration

• Autoconfiguration Server has a bank of addresses
• When a PC logs in, it gets a temporary IP
  number.
• Popular standards are DHCP (in Windows NT) and
  RARP
• Large stations receive permanent addresses

DHCP Request for Address
DHCP Server
DHCP Response Your Temporary Address
is 127.171.17.35
53
Autoconfiguration Protocol
Auto- Configuration Host
Source Host
Autoconfiguration Request Message
Source host sends Autoconfigutation
Request Message to the autoconfiguration
host My 48-bit MAC subnet address is X. Please
give me a 32-bit IP host address.
54
Autoconfiguration Protocol
Auto- Configuration Host
Source Host
Autoconfiguration Response Message
Autoconfiguration host sends back
a Autoconfiguration response message. Computer
at MAC Address X, your 32-bit IP host number is
110100.
55
Autoconfiguration Protocols

• RARP Reverse Address Resolution Protocol
• Older autoconfiguration protocol
• Bootp
• Another older protocol
• DHCP
• Dynamic Host Configuration Protocol
• Built into Windows NT Server

56
Domain Name Service

• Hosts also have IP host names
• Voyager.cba.hawaii.edu
• Like nicknames
• IP packets require formal IP numbers to put in
  their source and destination fields
• If tell your software the IP host name, it must
  look up the IP number

57
Domain Name Service

• Program knowing a host name sends request to
  Domain Name Service (DNS) Server receives IP
  Number

DNS Request for Voyager.cba.hawaii.edu
DNS Server
DNS Response 128.171.17.13
58
Domain Name System (DNS)
Source Host
DNS Host
DNS Request Message
Source host sends DNS Request Message to DNS
host. I need the 32-bit IP host number for the
host named voyager.cba.hawaii.edu.
59
Domain Name System (DNS)
Source Host
DNS Host
DNS Response Message
DNS host returns a DNS Reply Message. The 32-bit
host number is 128.171.44.53.
DNS Host
60
Domain Name System (DNS)
Source Host
DNS Host

• Each network has a DNS host
• May also have a secondary DNS host
• Network DNS host may only know the
• IP names and numbers of local hosts on
• the network
• For other IP names, contacts another
• DNS host, especially root DNS hosts,
• which should have extensive information

DNS Host
61
Internet Protocol Packet
Total Length (in Bytes)
Version
IHL
Type of Service
Fragment Offset
Identifier
Flags
Header Checksum
Time to Live
Protocol
Source Address
Current version is Version 4. A new
version, Version 6, is coming.
Destination Address
Options Plus Padding
Data
62
Internet Protocol Packet
Total Length (in Bytes)
Version
IHL
Type of Service
Fragment Offset
Identifier
Flags
Header Checksum
Time to Live
Protocol
There is only error checking for the header, not
for the entire packet. If an error is detected
in the header, the packet is discarded
63
Internet Protocol Packet
Total Length (in Bytes)
Version 4 addresses only have 32 bits. Not enough
for the number of Internet hosts. Will be raised
to 128 bits in Version 6
Fragment Offset
Header Checksum
Source Address (32 bits)
Destination Address (32 bits)
Options Plus Padding
Data