ROUTING PROTOCOLS

kindlyminnowNetworking and Communications

Oct 26, 2013 (3 years and 9 months ago)

83 views

ROUTING

Two types or routing are available: Static and Dynamic. In static routing, it configures the
routing table to set fixed paths between
the systems configuration, and the path on the
network never changes. Although a static router will recognize that

a link has gone down
and will issue an alarm, it will not automatically reroute traffic.


A dynamic router, on the other hand, reconfigures the routing table automatically and
recalculates the most efficient part in terms of load, line delay, or bandwidth
. Some
routers even balance the traffic load across multiple links, which enables. The various
links to better handle peak traffic conditions.


ROUTING PROTOCOLS


Each router on the network keeps a routing table and moved data along the network from
one ro
uter to the next by using routing protocols such as Open Shortest Path First
(OSPF), Intra
-
Autonomous System to Intra
-
Autonomous System (IS
-
IS), External
Gateway Protocol (EGP), Border Gateway Protocol (BGP), Inter
-
Domain Policy Routing
(IDPR), and Routing

Information Protocol (RIP).


Although still supported by many vendors, RIP does not perform well in today’s
increasingly complex networks. As the network expands, routing updates grow larger
under RIP and consume more bandwidth to route the information. W
hen a link fails, the
RIP updated procedure slows route discovery, increases network traffic and bandwidth
usage, and might cause temporary looping of data traffic. Also, RIP cannot calculate
routes based on such factors as delay and bandwidth, and its lin
e selection facility is
capable of choosing only one path to each destination.


The newer routing standard, OSPF, overcomes the limitations of RIP and even provides
capabilities that do not exit in RIP. The update procedure of OSPF requires that each
route
r on the network transmit a packet with a description of its local links to all other
routers. On receiving each packet, routing tables are built from the collected descriptions.
Because these description packets are relatively small, they produce a minimu
m of of
overhead. When a link fails, updated information floods the network, enabling all of the
routers to simultaneously calculate new tables.


Types of Routers

Multi
-
protocol nodal (or hub) routers are used for building
highly meshed wide
-
area
internets
. In addition to enabling several protocols to share the same logical network,
these devices pick the shortest path to the end node, balance the load across multiple
physical links, reroute traffic around points of failure or congestion, and implement flow

control in conjunction with the end nodes. They also pro
v
ide the means to tie remote
branch offices into the corporate backbone, which might use such WAN services TCP/IP,
T1, ISDN, and ATM. Some vendors also provide an interface for SMDS.


Access routers
are typically used
at branch offices. These are usually fixed
-
configuration
devices available in Ethernet and Token Ring versions, which support a limited number
of protocols and physical interfaces. They provide connectivity to high
-
end multi
-
protocols an
d physical interfaces. They provide connectivity to high
-
end multi
-
protocols
routers, enabling large and small nodes to be managed as a single logical enterprise
network. Although low
-
cost, plug
-
and
-
play bridges can meet the need for brach office
connectiv
ity, low
-
end routers can offer ore intelligence and configuration flexibility at a
comparable cost.


The newest access routers are multi
-
service devices, which are designed to handle a mix
of data, voice, and video traffic. They support a variety of WAN co
nnections through
built
-
in interfaces that include dual ISDN BRI interfaces, dual analog ports, T1/Frame
Relay Port, and an ISDN interface for video conferences. Such routers can run software
that provide IPSec VPN, firewall and encryption services.


Mid
-
r
ange routers provide network connectivity between corporate locations in support
of workgroups or the corporate
intranet, for example. These routers can be stand
-
alone
devices or packages as modules that occupy slots in an intelligent wiring hub or LAN
swi
tch. In fact, this type of router is often used to provide connectivity between multiple
wiring hubs or LAN switches over high
-
speed LAN backbones such as ATM, FDDI, and
Fast Ethernet.


A new class of
consumer routers are capable of providing shared access

to the Internet
over such broadband technologies as cable and DSL. The Linksys Instant Broadband
EtherFast Cable/DSL Router is used to connect a small group of PCs to a high
-
speed
Internet connection or to an Ethernet backbone. Configurable through any ne
tworked
PC’s Web browser, the router can be set up as a firewall and Dynamic Host
Configuration Protocol (DHCP) server, enabling it to act as an externally recognized
Internet device with its own IP address for the home LAN. Unlike a typical router which
c
an only share 100Mbps over all of its connections, the Linksys device is also equipped
with a four
-
port Ethernet switch that dedicates 100Mbps to every connected PC.


The Linksys router also supports Network
-
Address Translation (NAT), a feature that
transl
ates one public IP address, given by the cable or DSL Internet provider, and assigns
automatically up to 253 private IP addresses to users on the LAN. All of the users

who
are given an IP address by the router are safe behind the firewall so incoming and
o
utgoing requests are filtered, keeping unwanted requests off the LAN.


At the same time, the Linksys router supports a feature called DMZ/Expose Host, which
dissembles one of the 253 private IP addresses to become a public IP address so outside
users can a
ccess that PC without getting blocked by the firewall. An example would be a
gamer playing another gamer via the Internet. They want to access each other’s
computers so that they can play the game.


Summary

Routers fulfill a vital role in implementing comp
lex mesh networks. They also have
become an economical means of tying branch offices into the enterprise network and
providing PCs that are tied together on a home
network with shared access to broad
-
band
Internet services, such as cable and DSL. Similar t
o other interconnection devices, routers
are manageable via SNMP, as well as the proprietary
management systems of vendors.
Just as bridging and routing functions made their way into a single device, routing and
switching functions are being combined in th
e same way and even add firewall, DHCP,
and NAT capabilities.