Download ITP630_U4_Karloff_Boris_IT_ APA format

DYNAMIC ROUTING PROTOCOLS
Running head: CHOOSING A DYNAMIC ROUTING PROTOCOL
Choosing an Appropriate Dynamic Routing Protocol Based Upon
Predefined Specifications
Unit 4 Individual Project
Boris Karloff
Carnegie-Mellon University
Enterprise Network Design
ITP630-02
Professor Manny Astte, PhD
September 20, 2003
1
DYNAMIC ROUTING PROTOCOLS
Abstract
The transition from a static routing protocol to a dynamic
routing protocol can be a process fraught with difficulty or it
can be a process made easy by the selection of an appropriate
routing protocol.
An appropriate routing protocol is one that
will be compatible with your network, will be easy to
implement/maintain, and will suit the network needs of your
particular situation.
This paper will help to illuminate some
of the selection criteria to be considered for a given scenario
and will hopefully help you to match network requirements to the
protocol which has the closest matching characteristics.
2
DYNAMIC ROUTING PROTOCOLS
3
Choosing an appropriate dynamic routing protocol based upon
predefined specifications.
1) Preface – the given scenario presents a number of challenges
that must be addressed before a viable solution is arrived at.
The first challenge is that there are a number of unknowns
that make the determination of the best solution more
difficult.
The first unknown is “what type/brand of equipment
is being utilized.”
The use of proprietary solutions is
always geared towards one vendor or another.
One vendor’s
solutions often do not work with another vendor’s equipment.
Another unknown is “what staff is available and what
experience level does the staff have for the purpose of
implementing and maintaining complex dynamic routing protocols
in this scenario.” Making certain assumptions, therefore, will
be necessary to arrive at a “best” solution that addresses all
of the needs of the given scenario.
2) Given the following scenario, chose the best routing protocol
that meets the needs identified in the scenario.
a) “…You have been tasked with reconfiguring the network for
your company, which has grown considerably over the past
year. You have used only static routing in the past, but
you do not wish to spend the administrative time required
to maintain the routing tables now that the network has
grown. You have recently experienced numerous inaccuracies
DYNAMIC ROUTING PROTOCOLS
in the routing table cause by entries you made when in a
hurry. You would like to automate the entry and updating of
routing information, but you are concerned about excessive
memory and processor utilization if you implement dynamic
routing protocols…”
b) “…You also wish to minimize the use of network bandwidth.
You prefer that the most efficient use of bandwidth be made
so that packets will travel to their destination over the
truly shortest path, rather than just the path with the
lowest number of hops. You have heard that routing loops
can be a problem and wish to avoid them. However, you are
concerned that if a link goes down, there should be
redundancy so that traffic will go through…”
c) “How can you accomplish your objectives, and what routing
protocols and protocol features will you use to do so?”
3) Routing Protocols
a) Choosing a Routing Protocol – “…routing protocols are used
only to collect data about current network status and
contribute to the selection of the best path…”
(Dean, T.,
2002).
i) Classifications of Routing Protocols
(1)
Static versus dynamic
(2)
Single-path versus multi-path
(3)
Flat versus hierarchical
(4)
Host-intelligent versus router-intelligent
(5)
Intra-domain versus inter-domain
4
DYNAMIC ROUTING PROTOCOLS
5
b) In this scenario it is evident that a change from a static
routing protocol to a dynamic routing protocol needs to be
made.
c) Types of Dynamic Routing Protocols
i) Link-State Routing Protocols (LS) - “…This type of
routing protocol requires each router to maintain at
least a partial map of the network. When a network link
changes state (up to down, or vice versa), a
notification, called a link state advertisement (LSA) is
flooded throughout the network. All the routers note the
change, and re-compute their routes accordingly. This
method is more reliable, easier to debug and less
bandwidth-intensive than Distance-Vector. It is also more
complex and more compute- and memory-intensive…”
(FreeSoft.org, 2003).
The only limitation of link state
routing protocols is the complexity of maintaining these
complicated protocols, which scale well to large network
applications. Link state routing algorithms are also
known as Dijkstra Shortest Path algorithms.
The
following are a few examples of this type of routing
protocols.
(1)
OSPF
(2)
IS-IS
(3)
NLSP
(a)
NetWare Link Services Protocol
(b)
“…advanced link-state routing protocol developed
by Novell…” (Lammle, T. and Barkl, A., 2003).
DYNAMIC ROUTING PROTOCOLS
(c)
6
“…intended to replace both RIP and SAP [service
advertising protocol]…”
(Lammle, T. and Barkl, A.,
2003).
(d)
The NetWare Link Services Protocol (NLSP™)
provides link state routing for Internetwork Packet
Exchange networks (IPX). It is a protocol for
information exchange among routers geared to the
needs of large IPX networks.
(e)
Route Summarization
(i)
“…The benefits of summarization are derived
through efficient resource utilization. Since
multiple addresses can be summarized as a single
routing entry, the number of Link State Packets
(Lisps) can be reduced, thus minimizing the
amount of bandwidth required for routing
updates…” (Cisco Systems, 2003).
ii)
Distance-Vector Routing Protocols (DV) - “…This type
of routing protocol requires that each router simply
inform its neighbors of its routing table. For each
network path, the receiving routers pick the neighbor
advertising the lowest cost, then add this entry into its
routing table for re-advertisement…”
2003).
(FreeSoft.org,
Distance vector routing protocols are usually
limited to small networks consisting of fewer than 100
routers.
In order to avoid routing loops, distance
vector routing protocols use such techniques as “counting
to infinity,” “split horizon,” “[reverse] route
DYNAMIC ROUTING PROTOCOLS
poisoning,” and “hold-downs.”
Distance vector routing
algorithms are also known as Bellman-Ford routing
algorithms and Ford-Fulkerson routing algorithms.
(HowStuffWorks.com, 2003). The following are a few
examples of this type of protocol.
(1)
RIP
(2)
RIP-2
(3)
RTMP
(4)
IGRP
(5)
Hello Routing Protocol
(6)
EGP
iii) Balanced Hybrid/Balanced Routing Protocols - balanced
hybrid routing protocols have some of the best features
of both distance-vector routing protocols and link-state
routing protocols. An example of one protocol of this
type follows.
(1)
EIGRP
(a)
Enhanced Interior Gateway Routing Protocol
(b)
Uses the same route metrics as IGRP (see IGRP
above).
(c)
“…developed in the mid-1980s by Cisco Systems…”
(Dean, T., 2002).
(d)
“…it has a fast convergence time and a low
network overhead…”
(e)
(Dean, T., 2002).
“…is easier to configure and less CPU-intensive
than OSPF…”
(Dean, T., 2002).
7
DYNAMIC ROUTING PROTOCOLS
(f)
8
“…EIGRP…uses distance-vector and link-state
information when calculating routes using the DUAL
algorithm…convergence is much faster than with
IGRP…”
(g)
(Lammle, T. and Barkl, A., 2003).
“…also offers the benefits of supporting multiple
protocols and limiting unnecessary network traffic
between routers…”
(h)
“…accommodates very large and heterogeneous
networks…”
(i)
(Dean, T., 2002).
(Dean, T., 2002).
“…is only supported by Cisco routers…”
(Dean,
T., 2002).
(j)
“…uses the same vector information as IGRP…”
(Lammle, T. and Barkl, A., 2003).
(k)
“…EIGRP employs four key technologies, including
neighbor discovery/recovery, Reliable Transport
Protocol (RTP), Diffusion Update Algorithm (DUAL)
finite-state machine, and a modular architecture
that enable support for new protocols to be easily
added to an existing network…”
iv)
(Cisco.com, 2003).
Path State Routing Protocols – These exterior gateway
protocols are usually only used to route datagrams
between autonomous systems and are seldom seen inside of
an autonomous system.
type of protocol.
(1)
GGP
(2)
BGP-4
4) Selection Criteria
The following are examples of this
DYNAMIC ROUTING PROTOCOLS
9
a) Minimize the use of network bandwidth
i) No periodic updates – Only the link state protocols meet
the selection criteria of not sending out periodic
updates, but instead only multicasting changes when they
are necessary.
ii)
Routing protocols that do not send out periodic
updates make better use of available bandwidth than do
those which must send full updates every few seconds.
b) Packets should use the shortest path, rather than just the
path with the lowest number of “hops.”
i) Intelligent route “metrics”
ii)
Shortest Path First – Dijstra Algorithm
iii) Distance-Vector (DS) routing protocols only consider
the number of hops (or routers) between source and
destination.
iv)
Link-state routing protocols more intelligently
calculate the best route based upon several metrics
(depending upon the link-state routing protocol chosen).
c) Avoid routing loops – most routing protocols suffer from
the tendency to create routing loops.
Several techniques
exist with link-state and hybrid routing protocols to avoid
routing loops.
i) Spanning Tree Algorithm – used by the Spanning Tree
Protocol to prevent routing loops.
ii)
Spanning Tree Protocol - “…Spanning-Tree Protocol is a
link management protocol that provides path redundancy
while preventing undesirable loops in the network. For an
DYNAMIC ROUTING PROTOCOLS
10
Ethernet network to function properly, only one active
path can exist between two stations…” (Cisco Systems,
2003).
d) Automatic selection of alternate routes if critical links
go “down.”
i) Spanning Tree Protocol
(1)
Redundancy – “…To provide path redundancy,
Spanning-Tree Protocol defines a tree that spans all
switches in an extended network. Spanning-Tree
Protocol forces certain redundant data paths into a
standby (blocked) state…”
(2)
(Cisco Systems, 2003).
Fault Tolerance – “…. If one network segment in
the Spanning-Tree Protocol becomes unreachable, or if
Spanning-Tree Protocol costs change, the spanning-tree
algorithm reconfigures the spanning-tree topology and
reestablishes the link by activating the standby
path…”
(Cisco Systems, 2003).
5) Matching Protocols
a) OSPF
b) EIGRP
c) NLSP
6) Conclusion – depending upon the brand of equipment used for
routing devices and depending upon the selection of protocols
to be routed, the link-state routing protocols NLSP (for IPX)
or OSPF (for IP) or the hybrid routing protocol EIGRP could be
used to meet all of the criteria specified as important to
this client.
The best choice of protocols, equipment
DYNAMIC ROUTING PROTOCOLS
11
permitting, would probably the proprietary Cisco protocol,
EIGRP.
If the routers on this client’s network were not all
Cisco, though, that would be impossible, as EIGRP is only
useable on Cisco equipment.
If only Cisco equipment is
available, EIGRP becomes the best choice because of its
support of IP, AppleTalk, and the IPX protocols.
If EIGRP
cannot be used, the second best choice, if the IPX protocol
were the only protocol present on the network, would be NLSP.
If, instead, the TCP/IP protocol were being used, then the
OSPF routing protocol would be the second best choice of a
routing protocol. The use of OSPF, along with the features of
the Spanning Tree Algorithm, part of the Spanning Tree
Protocol, can be used to avoid routing loops,
DYNAMIC ROUTING PROTOCOLS
12
References
Cisco Systems (2003). Internetworking Technology Handbook.
Retrieved on September 14, 2003 from
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc .
Dean, T. (2002). Network+ Guide to Networks. 2nd Ed. Course
Technology, Boston, MA. PP. 90, 283-285
FAQS.org (2003).
What IP routing protocol should I use?
Internet FAQ Archives. Retrieved on September 14, 2003 from
http://www.faqs.org/faqs/cisco-networking-faq/section28.html .
FreeSoft.org (2003). Connected: An Internet Encyclopedia –
Routing.
Retrieved on September 14, 2003 from
http://www.freesoft.org/CIE/Topics/87.htm .
HowStuffWorks.com (2003).
How Routing Algorithms Work.
Retrieved on September 14 2003 from
http://computer.howstuffworks.com/routing-algorithm1.htm .
Lammle, T. and Barkl, A. (2003). CCDA Cisco Certified Design
Associate. 2nd Ed. SYBEX, Inc. Alameda, CA. PP. 137, 311-354