Transcript Repeaters, Switches and Routers

Repeaters, Switches
and Routers
This presentation will focus on network
hardware used to support Ethernet
networks
Repeaters, Switches
and Routers
Repeater:

A Physical Layer device that regenerates
digital signals, bringing them back to
standard form, and transferring each bit
from one LAN segment to another.
Repeaters, Switches
and Routers
Cisco Fasthub 100 series Repeater
Repeaters, Switches
and Routers
Repeater
This is the least complex and least
expensive of the three devices
 It operates on Layer 1 of the OSI model
 Typically no configuration required
 It deals with one bit at a time
 It knows nothing about addresses

Repeaters, Switches
and Routers
Repeater
Any signal coming in on one port is sent
out on all other ports
 It has the lowest latency of any of these
three devices
 It has the least memory and processing
power of any of these three devices

Repeaters, Switches
and Routers
Repeater
Usually people say Repeater when they
mean Multiport Repeater
 When someone refers to a Hub, they are
usually referring to a Multiport Repeater
 Although you can repeat any digital signal,
these days people usually mean a UTP
Ethernet repeater

Repeaters, Switches
and Routers
Repeater
Repeaters require no configuration, but
can often be configured to support
protocols like SNMP.
 A true repeater can regenerate a signal
from any media to any media, but it can’t
change the data rate of the signal between
ports

Repeaters, Switches
and Routers
Repeater
Devices on a network can’t detect when a
repeater is being used on a network
 Repeaters allow collisions to pass,
therefore all devices connected to a
repeater or series of repeaters are on the
same collision domain.

Repeaters, Switches
and Routers
A repeater was originally installed when
we wanted to extend the network
beyond the maximum cable length
allowed by 802.3. A repeater
regenerated the signal allowing for a
longer network.
Repeaters, Switches
and Routers
Repeaters, Switches
and Routers
Repeaters are rarely used in
commercial installations any more.
Switch prices have come down to be
very competitive in price with repeaters,
and they provide considerably improved
functionality
Most repeaters that are sold are now
used in a home network.
Repeaters, Switches
and Routers
A typical Bridge:
It is a Layer 2 device that understands
Frames
 Has only two ports
 Learns the MAC address of each host by
looking at the transmitted frames
 No configuration is required
 A bridge breaks up collision domains

Repeaters, Switches
and Routers
Bridge:
It will pass a broadcast, but will isolate
unicast traffic, allowing separate
simultaneous conversations on each side
of the bridge
 Bridges are often installed to improve the
performance of a network with too high of a
collision rate

Repeaters, Switches
and Routers
Bridge:
Bridges do more processing than a
multiport repeater because they assemble
Frames and do error detection and
correction
 The value of bridges can be defeated by a
broadcast intensive Network Operating
System

Repeaters, Switches
and Routers
Bridge:
Bridges were commonly selected to
provide a transition from one media type to
another, e.g. from coax to UTP
 Repeaters can also provide that transition
 However, with bridges, ports can run at
differing data rates

Repeaters, Switches
and Routers
Bridge:
Repeaters, Switches
and Routers
Switch
A Multiport bridge is called a switch
 It performs the same functions as a bridge
 It is typically used within a LAN and
requires no configuration.
 It requires a lot of memory to buffer data as
it comes in on each port

Repeaters, Switches
and Routers
Repeaters, Switches
and Routers
Switch
It has more latency than a repeater
because of the data buffering requirement
 The amount of RAM required is related to
the number of hosts supported per port
 The amount of RAM is also related to the
switching method

Repeaters, Switches
and Routers
Switch

Switches typically use one of three
selectable switching methods:
Cut Through
 Fragment Free
 Store and Forward

Repeaters, Switches
and Routers
Switch

Cut Through: A frame begins coming in
through a port. As soon as the address of
a frame is received and before the entire
frame is received, the destination address
is looked up in it’s address table and the
frame is sent out.
Repeaters, Switches
and Routers
Switch
Cut Through: The frame is typically not yet
completely received, nor is error detection
and correction completed. It provides for
extremely fast switching but often
increases the number of errors, especially
on a busy network
 Errors take a heavy toll on the network

Repeaters, Switches
and Routers
Switch

Fragment Free: This allows the first 64
Bytes of the frame to be received. Since
64 bytes is the minimum size of an
Ethernet packet, enough time has passed
for all devices on the network to recognize
there is traffic out there and a collision that
would cause a fragment is less likely.
Repeaters, Switches
and Routers
Switch

Fragment Free: Error detection is only
done on minimum size frames since the
FCS field is not received by the time the
other frames are switched. This technique
is still a pretty low latency method of
switching and it provides a significant
improvement in numbers of errors over cutthrough because many packets are only 64
bytes long.
Repeaters, Switches
and Routers
Switch

Store-and-forward: With this method the
entire frame is received before it is
forwarded on to the destination port. Error
checking is completed, so errors are not
forwarded. Latency, though, goes way up.
This is the best choice for a very busy
network. Can you understand why?
Repeaters, Switches
and Routers
Switch

Early on people recognized that switches
could provide different data rates for
different ports, effectively giving priority to
one port over another.
Repeaters, Switches
and Routers
Cisco 2950 series Switches
Repeaters, Switches
and Routers
Cisco 4500 series Switches
Switch
Ethernet
Repeaters, Switches
and Routers
7x
8x
9x
1x
2x
3x
10x 11x 12x
7x
8x
9x
4x
1x
2x
3x
10x 11x 12x
C
7 8 9 101112
A
123456
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10 Mbps
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Switch
10 Mbps 100 Mbps
10 Mbps
Server
Repeaters, Switches
and Routers
Switch
We migrated from bridging LAN segments
to putting a single host on each port, which
is the preferred configuration today.
 Repeaters, bridges and routers are almost
absent from LANs now because of modern
switches

Repeaters, Switches
and Routers
Switch
Spanning Tree Protocol: This allows a
network engineer to include a redundant
link, so if one link fails, another is already
queued up to carry the data.
 Without some way of dealing with
redundant links (sometimes called loops),
broadcast storms occur

Repeaters, Switches
and Routers
Switch

A broadcast storm occurs when a
broadcast goes around a loop and enters a
single switch from two different segments.
In that case, switches keep forwarding
frames out more than one port, so they are
forwarding frames to themselves.
Repeaters, Switches
and Routers
Switch

Spanning Tree is a protocol that is used
strictly between switches that allow them to
negotiate a root bridge, and then
temporarily turn off (block) one or more
port to break up the loop. If a network link
failure occurs, the blocked port is
reactivated.
Repeaters, Switches
and Routers
Switch
The organizer of this action is the “root”
switch, which stays in communication with
all other switches.
 The “root” switch is elected by comparing
the priority settings of each switch.
Conflicts are resolved by comparing MAC
addresses. The lowest number wins.
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Repeaters, Switches
and Routers
Switch
In the event of multiple connections to the
root switch, ports are assigned a cost
figure. (See table 2.1). The lowest cost is
associated with the highest data rate, and
it becomes the port used.
 Blocking and port selection decisions are
made from the perspective of the root
switch.

Repeaters, Switches
and Routers
Switch
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Many switch manufacturers recognize the
problems a loop can cause but are
unwilling to implement STP because of its
complexity and delay (50 seconds for
convergence). Instead they isolate links
that cause a loop.
Repeaters, Switches
and Routers
Router
Layer 3 devices
 Routers are put at the edge of a network
 They define the end of a network
 They are the most common devices used
to provide access to a WAN

Repeaters, Switches
and Routers
Router
They can help you logically segment your
network
 They block broadcasts
 Routers are typically much more expensive
than repeaters or switches
 Routers typically cause much higher
latencies than switches

Repeaters, Switches
and Routers
Router
They buffer the complete packet before
making a forwarding decision
 Error detection occurs on the header
 Traditionally used to interconnect two
dissimilar LANs (eg ATM and Token Ring).
More recently have lost this role to
Switches.

Repeaters, Switches
and Routers
Router
A complex routing protocol is employed to
accommodate multiple links between
routers
 They are much more software based than
switches
 Routers can be configured to block or pass
specific protocols, provide NAT, and other
functions

Repeaters, Switches
and Routers
Router
These devices require a much greater
processing capability
 You typically (Cisco) pay for each protocol
that is included
 Each router manufacturer has its own
unique operating system

Repeaters, Switches
and Routers
SoHo Router
Repeaters, Switches
and Routers
Cisco 2600 series Routers
Repeaters, Switches
and Routers
Cisco 12000 series Routers
Repeaters, Switches
and Routers
WAN
Router
Router
Switch
Switch
Workstation
Workstation
Workstation
Workstation
Workstation
Workstation
Repeaters, Switches
and Routers
Router
Typically must be manually configured
 It works harder and transfers data more
slowly than either repeaters or switches
 Routers used to be employed within a LAN
but are now rarely used that way because
of the impact on traffic

Repeaters, Switches
and Routers
Wireless
Repeaters, Switches
and Routers
Where are the Bus cables?
Coaxial bus cables are rarely used in
modern LAN installations
 All of the high speed LAN standards are
designed for UTP and Fiber, not on bus
cables.
 Star and Tree structures are used almost
exclusively in LANs

Repeaters, Switches
and Routers
Where are the fiber interfaces?
Where are the UTP interfaces?
Where are the WAN interfaces?
Where are the console interfaces?
Repeaters, Switches
and Routers
Modern hardware can be purchased
with whatever interface you choose to
pay for.
Repeaters and switches come with UTP
interfaces on most ports
Some hardware has modular ports,
allowing for some flexibility, but it comes
at a price
Repeaters, Switches
and Routers
Routers are most likely to have the most
flexibility with regard to interface.
They will have multiple LANs and WANs
Switches often have configurations that
provide for a higher speed uplink port.
Repeaters, Switches
and Routers
VLAN: Virtual Local Area Network
Defines Broadcast Domains
 Dynamically configured

By protocol
 By IP address
 By authenticated login
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
Port configured