chickpeasulotrichousΔίκτυα και Επικοινωνίες

27 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

66 εμφανίσεις

Mr. R. M. Pethe, Miss S. R .Burnase
Electronics and Communication, Nagpur University, Priyadarshini Instutute of Engg. & Technology, India, Nagpur
Electronics and Communication, Nagpur University, Priyadarshini Instutute of Engg. & Technology, India, Nagpur
Abstract— Interior Gateway Routing Protocol (IGRP) is a
distance-vector routing protocol while Enhanced Interior
Gateway Routing Protocol (EIGRP) is an advanced distance-
vector routing protocol. As the name implies, EIGRP is better
than IGRP. So, we hypothesized network using EIGRP will
have a better routing performance. This paper consist of
comparisons of OSPF, IGRP and RIP with EIGRP, also there
are problems with redistributing routes between RIP ,OSPF or
IGRP than in case of EIGRP. This paper also includes the
various trouble resolving techniques and traffic handling
techniques during communication in simple as well as in bulky
Key Words :- Computer Networking, Network Simulation, Router
Due to the limitations of Routing Information
Protocol (RIP), in the mid-1980s Cisco Systems,
Inc created IGRP to overcome the problems. IGRP
is an interior gateway protocol (IGP) which is a
distance-vector routing protocol used within an
autonomous system (AS). EIGRP is an advanced
distance-vector routing protocol that relies on
features commonly associated with link-state
protocols. OSPF's best traits, such as partial
updates and neighbor discovery, are similarly put
to use by EIGRP.
As we mentioned before, IGRP is a distance-
vector Interior Gateway Protocol (IGP). Distance-
vector routing protocols mathematically compare
routes using some measurement of distance. This
measurement is known as the distance vector.
Routers using a distance vector protocol must send
all or a portion of their routing table in a routing-
update message at regular intervals to each of their
neighboring routers. As routing information
distributes through the network, routers can
identify new destinations as they are added to the
network, learn of failures in the network, and
calculate distances to all known
destinations.EIGRP is also a distance-vector
Interior Gateway Protocol, which evolved from
IGRP. Which means that it saves the distance such
as hop count and a vector such as next hop when
determining the best path to a destination. Creation
of EIGRP is to answer the increasing needs in
networking and demands of diverse, large-scale
internetworks. EIGRP transports the subnet mask
information, which makes it a Classless routing
protocol. EIGRP contains an important protocol
called Diffusing update algorithm (DUAL)
developed at SRI International by Dr. J.J. Garcia-
DUAL enables EIGRP routers to determine
whether a path advertised by a neighbor is looped
or loop-free, and allows a router running EIGRP to
find alternate paths without waiting on updates
from other routers. Therefore, EIGRP minimizes
both the routing instability triggered by topology
changes and the use of bandwidth and processing
power in the router. When a change in the network
happens, the routers with EIGRP sends out just the
changes to the routing table. Also the EIGRP is
not limited to the number of Hops so it can reach
out very far without slowing down.
We can also note that IGRP does not support
VLSM where EIGRP does. VLSM (variable
length subnet masking) allows you to subdivide a
classful network into subnets. Also be aware that
EIGRP and IGRP are compatible with each other.
An automatic-redistribution mechanism allows
IGRP routes to be imported into EIGRP, and vice
versa. Because the metrics for both protocols are
directly translatable, they are easily comparable.
IGRP and EIGRP path selection is based on
Bandwidth/Delay metric. Using some EIGRP
commands maximum bandwidth can be changed
as required.

EIGRP routers converge quickly because they
rely on a state-of-the-art routing algorithm
called the Diffusing Update Algorithm
EIGRP makes efficient use of bandwidth by
sending partial, bounded updates and its
minimal consumption of bandwidth when the
network is stable.
EIGRP offers full support for classless IP by
exchanging subnet masks in routing updates.
EIGRP supports IP, IPX, and AppleTalk
through protocol-dependent modules (PDMs).
PDMs protect EIGRP from painstaking
revision. Evolution of a routed protocol, such
as IP, may require a new protocol module, but
not necessarily a reworking of EIGRP itself.
EIGRP supports for IPX: In this
Time-driven protocols, IPX RIP and SAP,
generate updates every 60 seconds by default.
These updates can crowd low-speed WAN
links, especially in large internetworks. An
EIGRP router will receive routing and service
updates and then update other routers only
when changes in the SAP or routing tables
occur. Routing updates occur as they would in
any EIGRP network - using partial updates,
thus conserving bandwidth on the low-speed
WAN links. neighbor table listing adjacent
routers, comparable to the OSPF adjacency
Some terms are given below.
· Topology table - Every EIGRP
router maintains a topology table for each
configured network protocol showing all
learned routes to a destination.
· Routing table - EIGRP chooses the
best routes to a destination from the topology
table and places these routes in the routing table.
· Successor - A successor is a route
selected as the primary route to use to reach a
destination. Multiple successors for a
destination can be retained in the routing table.
· Feasible successor - A feasible
successor is a backup route. Multiple feasible
successors for a destination can be retained in
the topology table.
EIGRP has the following four basic
1.Neighbor discovery of
neighbor recovery
2.Reliable transport protocol
3.DUAL finite state machine
4.Protocol-dependent modules
Neighbor discovery of neighbor
recovery is the process that routers use to
dynamically learn of other routers on their
directly attached networks. Routers must also
discover when their neighbors become
unreachable or inoperative. Neighbor discovery
of neighbor recovery is achieved with low
overhead by periodically sending small hello
packets. As long as hello packets are received,
the Cisco IOS software can determine that a
neighbor is alive and functioning. Once this
status is determined, the neighboring routers
can exchange routing information.
The reliable transport protocol is
responsible for guaranteed, ordered delivery of
EIGRP packets to all neighbors. It supports
intermixed transmission of multicast and
unicast packets. Some EIGRP packets must be
sent reliably and others need not be. For
efficiency, reliability is provided only when
necessary. For example, on a multi-access
network that has multicast capabilities (such as
Ethernet) it is not necessary to send hello
packets reliably to all neighbors individually.
Therefore, EIGRP sends a single multicast
hello with an indication in the packet informing
the receivers that the packet need not be
acknowledged. Other types of packets (such as
updates) require acknowledgment, which is
indicated in the packet. The reliable transport
has a provision to send multicast packets
quickly when unacknowledged packets are
pending. This provision helps to ensure that
convergence time remains low in the presence
of varying speed links.EIGRP is protocol-
independent (i.e., it does not rely on TCP/IP to
exchange routing information the way that RIP,
IGRP, and OSPF do). To stay independent of
IP, EIGRP uses its own proprietary transport-
layer protocol to guarantee delivery of routing
information: RTP. Then EIGRP can call on
RTP to provide reliable or unreliable service as
the situation warrants.
The five EIGRP packet types are:
· Hello – used to discover, verify, and
rediscover neighbor routers. EIGRP routers send
hellos at a fixed but configurable interval, called
the hello interval. The default hello interval
depends on the bandwidth of the interface, 60
seconds for 1.54 mbps or less and 5 seconds for
more than 1.54 mbps. Hellos are sent multicast
to IP address
· Acknowledgment – sent as unicast to
indicate receipt of any EIGRP packet during a
"reliable" exchange.
· Update - used when a router
discovers a new neighbor or when a router
discovers a topology change. Sent unicast and
· Query - can be multicast or unicast,
used when routers need specific information
from one or all neighbors. Sent reliably.
· Reply - used to respond to a query.
Always sent as a unicast. Following table shows
the major differences in-between IGRP &
Classful Routing
Classless Routing
bandwidth =
idth kbps)
delay =
24 bit metric for
bandwidth and
bandwidth =
kbps) * 256
delay = (delay/10)
* 256
32 bit metric for
bandwidth and delay
Maximum Hop
Count = 255
Maximum Hop Count =
No differentiation
between internal
and external routes.
Outside routes
(redistributed) are
tagged as external
Automatic redistribution between IGRP and
EIGRP as long as “AS” numbers are the
Table no 1: Comparison between EIGRP & IGRP
Fig. 1 EIGRP and IGRP automatically redistributed roués
between autonomous systems with the same number
As shown in the given figure both IGRP and
EIGRP automatically redistributes routes
between autonomous systems with the same
number. Steps for this are given below
1.Automatic redistribution occurs when
the same AS number is used for EIGRP
and IGRP.
2.EIGRP scales the IGRP metric by a
factor of 256.
3.IGRP reduces the metric by a factor o
4.EIGRP will tag routes learned from
IGRP, or any outside source, as external
because they did not originate from
EIGRP routers.
5.IGRP cannot differentiate between
internal and external routes
6.Comparison of EIGRP with OSPF and
Following table shows the comparison points in-
between OSPF, RIP an EIGRP.
7.As mentioned before, the major
difference between IGRP and EIGRP is EIGRP
supports large-scale internetworks better than
IGRP. Our study intent is to compare
performance of a network using IGRP to that
using EIGRP. Therefore, we built two
internetworks, of each has 6 different physical
networks connect to each other, and each of
them uses different dynamic routing protocol,
i.e. either IGRP or EIGRP. In order to simulate
traffic within a network, we defined 3
applications, Database Application, HTTP and
Email, that would be used by the various nodes.
Troubleshooting steps for the successor failure
are given below for network using EIGRP
Fig. 2 By identifying feasible successors, EIGRP routers can
immediately install alternate routers if a successor fails.
Select Routes
• If a link goes down, DUAL looks for an
alternative route path, or feasible
successor, in the topology table.
• If a feasible successor is not found, the
route is flagged as Active, or unusable at
• Query packets are sent to neighboring
routers requesting topology information.
• DUAL uses this information to
recalculate successor and feasible
successor routes to the destination.
Troubleshooting Process steps are
given below for network using EIGRP.
1.Analyze the network failure, make a
clear problem statement.
2.Gather the facts needed to help isolate
possible causes.
3.Consider possible problems based on the
facts that have been gathered.
4.Create an action plan based on the
remaining potential problems.
5.Implement the action plan, performing
each step carefully while testing to see
whether the symptom disappears.
6.Analyze the results to determine whether
the problem has been resolved. If it has,
the process is complete.
7.If the problem has not been resolved,
create an action plan based on the next
most likely problem in the list. Return to
Step 4, change one variable at a time,
and repeat the process until the problem
is solved.
8.Once the actual cause of the problem is
identified, try to solve it.
· Unlike IGRP, which is a classful routing
protocol, EIGRP is classless.
· EIGRP boasts faster convergence times,
improved scalability, and superior handling of
routing loops.
· EIGRP can replace Novell RIP and
AppleTalk Routing Table Maintenance Protocol
(RTMP), serving both IPX and AppleTalk
networks with powerful efficiency.
• Proprietary to CISCO
• Routers from other vendors cannot use
or understand EIGRP
Our results show that EIGRP
provides much better network performance than
IGRP , RIP and OSPF. Means its te new
language of networking. EIGRP made a
noticable impact on the performance of the
network. For the HTTP application, EIGRP
made the most difference later in the test when
the amount of HTTP traffic increased beyond
that of the IGRP scenario. Even with the greater
amount of traffic the response time of the HTTP
server was still better than that of the IGRP
scenario. However, the performance of the
network was not always better when using
EIGRP. EIGRP network has on average greater
performance.If we were to add a larger network
with more hops, workstations and networks all
across the world, we believe we would notice a
much larger increase in difference between
EIGRP and IGRP. But even with our smaller
scale network we were able to prove that EIGRP
was a more effective protocol.
[1] Todd Lammle, Cisco Certified Network Associate, Study
Guide 5
[2] “Interior Gateway Routing Protocol.”Online, 14 April
2008. <>
[3] “Interior Gateway Routing Protocol (IGRP).” Online, 14
April 2008.
[4] “Enhanced Interior Gateway Routing Protocol.”Online, 14
April 2008. <>
[5] “Enhanced Interior Gateway Routing Protocol (EIGRP).”
Online, 14 April 2008.