Review: Interior Gateway Protocols

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Oct 28, 2013 (3 years and 1 month ago)

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Revi ew: I nt er i or Gat eway Pr ot ocol s
1
Lat eef Ahmad Bhat,
2
Vi s hal Sudan,
3
Ki r at pal s i ngh
Dept. of ECE, Surya World, Punjab, India
Abstract
An Interior Gateway Protocol (IGP) is a routing protocol which
is used to exchange routing information within routing domain or
autonomous systems. This paper consists of different classification
of Interior gateway routing protocols. This paper also includes the
comparison between IGRP, EIGRP, OSPF, protocols.
Keywords
IGP, Routing protocol, OSPF, EIGRP, IGRP, RIP, IS-IS.
I. Introduction
IGPs are used for routing within a routing domain i.e. those networks
within the control of a single organization. An autonomous system
is commonly comprised of many individual networks belonging
to companies, schools, and other organizations. An IGP is used
to route within the autonomous system, and also used to route
within the individual networks themselves. The IGP is mainly
classified into two:
Distance vector routing protocol•
Link state routing protocol•
1. Distance Vector Routing Protocol
It uses distance vector algorithm or Bellman ford algorithm. In
a distance vector algorithm, each router generates a map of its
paths to all connected nodes in the network and sends this map
to only its adjacent neighbors. A router using a distance vector
protocol records the distance (a metric) from it to the destination
and the next hop (which is the vector) to reach that destination
and communicates this to its neighbors. Previously hop count is
the only metric used by distance vector routing protocols, RIP
protocol is an example of distance vector routing protocols which
only uses hop count as metric. It also employs count-to-infinity
rules and split-horizon techniques for loop avoidance. After this
Distance vector interior gateway protocols were improved and
make uses of more than just the hop-count as a metric and can take
into account multiple link characteristics, such as bandwidth and
delay. Interior Gateway Routing Protocol (IGRP) is an example
and in this protocol additional loop avoidance techniques are built
in and generally it send updates and not full tables.
2. Link State Routing Protocol
It uses Dijkstra Algorithm. It is also called shortest path first
algorithm. Link state algorithm floods routing information to all
nodes in the network however, each router sends only the portion
of the routing table that describes the state of its own links. In
link-state algorithms, each router builds a picture of the entire
network in its routing tables. Open Shortest Path First (OSPF)
protocol is an example of link state routing protocol.
II Overview
A. Open Shortest Path First (OSPF)
It is an interior gateway link state protocol which is used to
allow routers to learn and advertise the routes dynamically.
The advertisements containing routes are referred to link state
advertisements. OSPF uses a hierarchical architecture. By having
a hierarchical design, routing control packets in the domain are
decreased and limited to a given area. OSPF allows a network
to be segmented into multiple areas. An area is a collection of
routers and networks.
A. Control Packets
Some control packets are used to guarantee neighbor discovery
and maintenance and database synchronization, the following
packet types are defined within the Type field of an OSPF control
packet.
Packet type Description
1 Hello
2 Data base description
3 Link state request
4 Link state update
5 Link state acknowledgement
Packet Type 1: Hello packets are used to establish connections and
guarantee neighbor discovery and is also used for maintenance.
Packet Type 2: Database Description packets are used in the initial
database synchronization.
Packet Type 3- During a database description exchange, the routers
requests their missing LSA.
Packet Type 4- A router replies to the Link State Request packet
by sending a Link State Update. Link State Update is also used
when the routers are in Full state and there is a need to generate
a new LSA due to any changes.
Packet type 5- The flooding operation should be reliable in order
to guarantee that no information was lost while synchronizing the
database. Link State Acknowledgment is sent in reply to a Link
State Update packet.
The three components in OSPF include:
Neighbor discovery •
Database synchronization•
Shortest Path First (SPF) calculation•
1. Neighbor Discovery
When OSPF is enabled on an interface; the router sends Hello
packets periodically in order to discover the remote neighbor’s.
When a router receives a Hello from its neighbor, it includes the
Router ID of this neighbor in its next Hello. This ensures that there
is two-way connectivity between routers. A Hello packet is also
used to elect DR/BDR on a multi-access network (broadcast and
NBMA) and make sure that the neighbors agree on the area type
based on the option fields in the Hello packet.
2. Database Synchronization
It is important that the database of all routers within an area is
synchronized in order so that they have the same view of the
network. Synchronization is either the initial router synchronization
or if there is any change to the network topology and the routers
need to resynchronize. Synchronization is performed by the way
of OSPF packet type 2, 3, 4, and 5. Once two routers achieve the
2-way state, they start synchronizing their database by establishing
a master-slave relationship. After the 2-way state, the routers go to
the Exstart state where they have to find out who is the master. This
is done by Router ID. The master sends a Database Description
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packet by i ncr ement i ng t he LS s equence f or ever y di f f er ent packet,
a nd t he s l a ve j us t e c hoe s ba c k t he LS s e que nc e numbe r s e nt by
t he ma s t e r. Onl y one Da t a ba s e De s c r i pt i on pa c ke t i s s e nt a nd
e c hoe d a t a t i me. Thi s gua r a nt e e s a r e l i a bl e e xc ha nge be t we e n
t he t wo r out e r s.
3. Shor t est Pat h Fi r st Cal cul at i on
Af t e r da t a ba s e s ync hr oni z a t i on, a l l r out e r s i n a n a r e a wi l l ha ve t he
e xa c t s a me l i nk s t a t e da t a ba s e. The da t a ba s e i s j us t a c ol l e c t i on
of di f f e r e nt LSAs t ha t t he r out e r ha s r e c e i ve d a nd s houl d bui l d
up t he r out i ng t a bl e ba s e d on t hi s i nf or ma t i on.
The r e a r e t wo t ype s of r out e s:
Ne t wor k r out e —a de s t i na t i on I P a ddr e s s e s.•
Rout e r r out e —The pa t h ( out goi ng i nt e r f a c e a nd ne xt hop)•
SPF ne e ds t o s e e t he ne t wor k a s a c ol l e c t i on of node s a nd poi nt -
t o- poi nt l i nks. A mul t i - a c c e s s ne t wor k i s r e pr e s e nt e d by a Ps e udo
node ( DR). Eve r y r out e r a nnounc e s a c onne c t i on t o t he t r a ns i t
ne t wor k ( DR) a nd t he DR a nnounc e s a c onne c t i on t o a l l a t t a c he d
r out er s. A r out er fir s t finds out t he pat h ( out goi ng i nt er f ace and next
hop) t o a l l t he node s i n i t s a r e a by r unni ng t he Di j ks t r a a l gor i t hm.
Onc e t he pa t h t o a l l t he node s i s f ound ( out goi ng i nt e r f a c e a nd
ne xt hop), t he pa t h t o a l l t he I P a ddr e s s e s a dve r t i s e d by t he node
i s c a l c ul a t e d.
B. Enhanced i nt er i or gat eway r out i ng pr ot ocol ( EI GRP) -
EI GRP i s a di s t a nc e - ve c t or I nt e r i or Ga t e wa y Pr ot oc ol, whi c h
evol ved f r om I GRP. EI GRP t r ans por t s t he s ubnet mas k I nf or mat i on,
whi c h ma ke s i t a Cl a s s l e s s r out i ng Pr ot oc ol. EI GRP c ont a i ns a n
i mpor t a nt pr ot oc ol c a l l e d Di f f us i ng upda t e a l gor i t hm ( DUAL).
EI GRP a l s o s uppor t s VLSM. EI GRP ma ke s e f fic i e nt us e of
ba ndwi dt h by s e ndi ng pa r t i a l, bounde d upda t e s a nd i t s mi ni ma l
consumption of bandwidth when the network is stable. An EIGRP
router will receive routing and service updates and then updates
other routers only when changes in the SAP or routing tables
occur. The EIGRP has four main components.
1. Protocol Dependant Modules (PDM)
EIGRP has a separate module for each of the three routed protocols
it supports, namely IP, IPX, and AppleTalk. The choice of routed
protocol deployed determines which PDM EIGRP uses.
2. Reliable Transport Protocol (RTP)
The Reliable Transport Protocol (RTP) is responsible for
guaranteed delivery of EIGRP packets and also ensures that
packets are delivered in order. EIGRP packets are sent via the
multicast address 224.0.0.10. Cisco has implemented a concept
of reliable multicast where each received multicast packet is
acknowledged via a unicast packet to the sender. [3]
3. Diffusing Update Algorithm (DUAL)
EIGRP uses the DUAL algorithm to calculate the best path to a
destination while guaranteeing a loop free topology. [4]
4. Hello Sub-Protocol
EIGRP employs a hello sub-protocol for neighbor discovery and
recovery, OSPF uses a similar protocol.
(i). EIGRP Protocol Concepts
Hello- It is a message of a routing protocol used for neighbor
discovery and tracking. In EIGRP, hello packets are sent to the
multicast address of 224.0.0.10.
Acknowledgements- Acknowledgements are sent in response to
hello packets. This is how EIGRP guarantees reliable delivery
and receipt.
Hello Timer- The interval between hello packets. In EIGRP, the
default is 5 seconds or 60 seconds depending on the underlying
media [4].
Hold Timer- The amount of time a router waits without receiving a
hello from a neighbor before marking it as no longer available.
Update- An update is a protocol message. An update is sent when
any of the following occurs:
when a neighbor first comes up•
when a router moves from Active to Passive state for any •
destination
when there is a metric increase for a given destination•
Query- Sent to all neighbors when a router enters a destination
into the Active state. The router will remain in the active state
unless it receives replies from all its neighbors.
Reply- Required response to a query. If the neighbor doesn’t have
the information, it will in turn send a query to its neighbors.
Active State- A router enters a destination into the Active State
when it has lost its successor to that destination and has no
feasible successor. The router must compute a new route to the
destination.
Passive State- A destination is said to be in the Passive State when
it has a feasible successor in the router’s topology table.
SIA (Stuck in Active) - A state where the router has not had a
response from a query packet for a predetermined time. The default
time is 3 minutes.
EIGRP uses the minimum bandwidth on the path to a destination
network and the total delay to compute routing metrics. The
bandwidth and delay metrics are determined from values configured
on the interfaces of routers in the path to the destination network.
Following formulae can calculate the metric of the EIGRP
Metric = [K1 * bandwidth + (K2 * bandwidth) / (256 − load) +
K3 * delay] * [K5 / (reliability + K4)]. [4]
The default values for K are:
K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0.
For default behavior metric can be calculated directly as
follows.
Metric = bandwidth + delay
Characteristics of EIGRP-
EIGRP adheres to the following characteristics:
EIGRP uses Diffusing Update Algorithm (DUAL) to •
determine the best path among all “feasible” paths. DUAL
also helps ensure a loop free routing environment.
EIGRP will form neighbor relationships with adjacent routers •
in the same Autonomous System (AS).
EIGRP traffic is either sent as uncast, or as multicasts on •
address 224.0.0.10, depending on the EIGRP packet type.
Reliable Transport Protocol (RTP) is used to ensure delivery •
of most EIGRP packets.
EIGRP routers do not send periodic, full-table routing updates. •
Updates are sent when a change occurs, and include only the
change.
EIGRP is a classless protocol, and thus supports VLSMs.•
EIGRP supports IP, IPX, and AppleTalk routing.•
EIGRP applies an Administrative Distance of 90 for routes •
originating within the local Autonomous System
EIGRP applies an Administrative Distance of 170 for external •
routes coming from outside the local Autonomous System.
EIGRP uses Bandwidth and Delay of the Line, by default, •
to calculate its distance metric. It also supports three other
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pa r a me t e r s t o c a l c ul a t e i t s me t r i c: Re l i a bi l i t y, Loa d, a nd
MTU.
EI GRP ha s a ma xi mum hop- c ount of 224, t hough t he de f a ul t •
ma xi mum hop- c ount i s s e t t o 100. [ 4]
C. I nt er i or Gat eway Rout i ng Pr ot ocol ( I GRP)
The I nt e r i or Ga t e wa y Rout i ng Pr ot oc ol ( I GRP) i s a r out i ng
pr ot oc ol t ha t wa s de ve l ope d i n t he mi d- 1980s by Ci s c o Sys t e ms,
I nc. Ci s c o’s pr i nc i pa l goa l i n c r e a t i ng I GRP wa s t o pr ovi de a
r obus t pr ot oc ol f or r out i ng wi t hi n a n Aut onomous Sys t e m ( AS).
I GRP i s de s i gne d t o be mor e s c a l a bl e t ha n RI P.
I GRP a dhe r e s t o t he f ol l owi ng c ha r a c t e r i s t i c s:
I GRP s e n d s o u t p e r i o d i c r o u t i n g u p d a t e s ( e v e r y 9 0 •
s e c onds ).
I GRP s e n d s o u t t h e f u l l r o u t i n g t a b l e e v e r y p e r i o d i c •
upda t e.
I GRP us e s a f or m of di s t a nc e a s i t s me t r i c ( i n t hi s c a s e, a •
c ompos i t e of ba ndwi dt h a nd de l a y).
I GRP us e s t he Be l l ma n- For d Di s t a nc e Ve c t or a l gor i t hm t o •
de t e r mi ne t he be s t “ pa t h” t o a pa r t i c ul a r de s t i na t i on.
I GRP s uppor t s onl y I P r out i ng.•
I GRP r out e s ha ve a n a dmi ni s t r a t i ve di s t a nc e of 100.•
I GRP, by de f a ul t, s uppor t s a ma xi mum of 100 hops. Thi s •
va l ue c a n be a dj us t e d t o a ma xi mum of 255 hops.
I GRP i s a c l a s s f ul r out i ng pr ot oc ol. [ 4]•
I GRP us es Bandwi dt h and Del ay of t he Li ne, by def aul t, t o cal cul at e
i t s di s t a nc e me t r i c. Re l i a bi l i t y, Loa d, a nd MTU a r e opt i ona l
a t t r i but e s t ha t c a n be us e d t o c a l c ul a t e t he di s t a nc e me t r i c.
The ge ne r a l f or mul a e whi c h i s us e d t o c a l c ul a t e t he Me t r i c i s
gi ve n be l ow:
Me t r i c = [ K1 * ba ndwi dt h + ( K2 * ba ndwi dt h) / ( 256 − l oa d) +
K3 * de l a y] * [ K5 / ( r e l i a bi l i t y + K4) ].
The de f a ul t va l ue s f or K a r e:
K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0 [ 4]
St a bi l i t y Fe a t ur e s -
I GRP pr ovi de s a numbe r of f e a t ur e s t ha t a r e de s i gne d t o e nha nc e
i t s s t a bi l i t y. The s e i nc l ude
Hol d- downs, s pl i t hor i z ons, a nd poi s on r e ve r s e upda t e s.
Hol d- Downs - Hol d- downs a r e us e d t o pr e ve nt r e gul a r upda t e
me s s a ge s f r om i na ppr opr i a t e l y r e i ns t a t i ng a r out e t ha t ma y ha ve
gone bad. When a r out er goes down, nei ghbor i ng r out er s det ect t hi s
vi a t he l ack of r egul ar l y s chedul ed updat e mes s ages. Thes e r out er s
t he n c a l c ul a t e ne w r out e s a nd s e nd r out i ng upda t e me s s a ge s t o
i nf or m t hei r nei ghbor s of t he r out e change. Hol d- downs t el l r out er s
t o hol d down a ny c ha nge s t ha t mi ght a f f e c t r out e s f or s ome pe r i od
of t i me.
Spl i t Hor i z ons - Spl i t hor i z ons de r i ve f r om t he f a c t t ha t i t i s ne ve r
us e f ul t o s e nd i nf or ma t i on a bout a r out e ba c k i n t he di r e c t i on f r om
whi c h i t c a me. The s pl i t - hor i z on r ul e he l ps pr e ve nt r out i ng l oops.
Spl i t hor i z ons a r e i mpl e me nt e d i n I GRP be c a us e t he y pr ovi de
e xt r a a l gor i t hm s t a bi l i t y.
Poi s on Re ve r s e Upda t e s - Whe r e a s s pl i t hor i z ons s houl d pr e ve nt
r out i ng l oops be t we e n a dj a c e nt r out e r s, poi s on r e ve r s e upda t e s
a r e i nt e nde d t o de f e a t l a r ge r r out i ng l oops. I nc r e a s e s i n r out i ng
me t r i c s ge ne r a l l y i ndi c a t e r out i ng l oops. Poi s on r e ve r s e upda t e s
a r e t he n s e nt t o r e move t he r out e a nd pl a c e i t i n hol d- down. I n
Ci s c o’s i mpl e me nt a t i on of I GRP, poi s on r e ve r s e upda t e s a r e s e nt
i f a r out e me t r i c ha s i nc r e a s e d by a f a c t or of 1.1 or gr e a t e r.
1. I GRP Ti mer s- I GRP has Four Basi c Ti mer s
Updat e Ti mer ( def aul t 90 s econds ) – i ndi cat es how of t en t he r out er
wi l l s e nd out a r out i ng t a bl e upda t e.
I nva l i d Ti me r ( de f a ul t 270 s e c onds ) – i ndi c a t e s how l ong a r out e
wi l l r e ma i n i n a r out i ng t a bl e be f or e be i ng ma r ke d a s i nva l i d, i f
no ne w upda t e s a r e he a r d a bout t hi s r out e. The i nva l i d t i me r wi l l
be r e s e t i f a n upda t e i s r e c e i ve d f or t ha t pa r t i c ul a r r out e be f or e
t he t i me r e xpi r e s.
A r out e ma r ke d a s i nva l i d i s not i mme di a t e l y r e move d f r om
t he r out i ng t a bl e. I ns t e a d, t he r out e i s ma r ke d ( a nd a dve r t i s e d)
wi t h a me t r i c of 101 ( r e me mbe r, 100 ma xi mum hops i s de f a ul t ),
i ndi c a t i ng i t i s unr e a c ha bl e, a nd pl a c e d i n a hol d- down s t a t e.
Hol d- down Ti me r ( de f a ul t 280 s e c onds ) – i ndi c a t e s how l ong
I GRP wi l l “ s uppr e s s ” a r out e t ha t i t ha s pl a c e d i n a hol d- down
s t a t e. I GRP wi l l not a c c e pt a ny ne w upda t e s f or r out e s i n a hol d-
down s t a t e, unt i l t he hol d- down t i me r e xpi r e s.
Fl us h Ti mer ( def aul t 630 s econds ) – i ndi cat es how l ong a r out e can
r e ma i n i n a r out i ng t a bl e be f or e be i ng flus he d, i f no ne w upda t e s
a r e he a r d a bout t hi s r out e. The flus h t i me r r uns c onc ur r e nt l y wi t h
t he i nva l i d t i me r, a nd t hus wi l l flus h out a r out e 360 s e c onds a f t e r
i t ha s be e n ma r ke d i nva l i d.
D. Rout i ng I nf or mat i on Pr ot ocol ( RI P)
The Rout i ng I nf or mat i on Pr ot ocol, or RI P, as i t i s mor e commonl y
c a l l e d, i s one of t he mos t e ndur i ng of a l l r out i ng pr ot oc ol s. RI P i s
a l s o one of t he mor e e a s i l y c onf us e d pr ot oc ol s. Ri p us e s t he s a me
Al gor i t hm t ha t us e di s t a nc e ve c t or t o ma t he ma t i c a l l y c ompa r e
r out e s t o i de nt i f y t he be s t pa t h t o a ny gi ve n de s t i na t i on a ddr e s s.
Rout i ng Upda t e s - RI P s e nds r out i ng- upda t e me s s a ge s a t r e gul a r
i nt e r va l s a nd whe n t he ne t wor k t opol ogy c ha nge s. Whe n a r out e r
r e c e i ve s a r out i ng upda t e t ha t i nc l ude s c ha nge s t o a n e nt r y, i t
upda t e s i t s r out i ng t a bl e t o r e fle c t t he ne w r out e. The me t r i c va l ue
f or t he pa t h i s i nc r e a s e d by 1, a nd t he s e nde r i s i ndi c a t e d a s t he
ne xt hop. RI P r out e r s ma i nt a i n onl y t he be s t r out e ( t he r out e wi t h
t he l owes t met r i c val ue) t o a des t i nat i on. Af t er updat i ng i t s r out i ng
t a bl e, t he r out e r i mme di a t e l y be gi ns t r a ns mi t t i ng r out i ng upda t e s
t o i nf or m ot he r ne t wor k r out e r s of t he c ha nge. The s e upda t e s a r e
s e nt i nde pe nde nt l y of t he r e gul a r l y s c he dul e d upda t e s t ha t RI P
r out e r s s e nd.
RI P s t a bi l i t y f e a t ur e - RI P pr e ve nt s r out i ng l oops f r om c ont i nui ng
i nde fini t e l y by i mpl e me nt i ng a l i mi t on t he numbe r of hops
a l l owe d i n a pa t h f r om t he s our c e t o a de s t i na t i on. The ma xi mum
numbe r of hops i n a pa t h i s 15. I f a r out e r r e c e i ve s a r out i ng
upda t e t ha t c ont a i ns a ne w or c ha nge d e nt r y, a nd i f i nc r e a s i ng
t he me t r i c va l ue by 1 c a us e s t he me t r i c t o be i nfini t y ( t ha t i s, 16),
t he ne t wor k de s t i na t i on i s c ons i de r e d unr e a c ha bl e. The downs i de
of t hi s s t a bi l i t y f e a t ur e i s t ha t i t l i mi t s t he ma xi mum di a me t e r
of a RI P ne t wor k t o l e s s t ha n 16 hops. RI P i mpl e me nt s t he s pl i t
hor i z on a nd hol ddown me c ha ni s ms t o pr e ve nt i nc or r e c t r out i ng
i nf or ma t i on f r om be i ng pr opa ga t e d.
RI P t i mer s - RI P us es numer ous t i mer s t o r egul at e i t s per f or mance.
The s e i nc l ude a r out i ng- upda t e t i me r, a r out e - t i me out t i me r, a nd
a r out e - flus h t i me r. The r out i ng upda t e t i me r c l oc ks t he i nt e r va l
bet ween per i odi c r out i ng updat es. Gener al l y, i t i s s et t o 30 s econds,
wi t h a s ma l l r a ndom a mount of t i me a dde d whe ne ve r t he t i me r
i s r e s e t. Thi s i s done t o he l p pr e ve nt c onge s t i on, whi c h c oul d
r e s ul t f r om a l l r out e r s s i mul t a ne ous l y a t t e mpt i ng t o upda t e t he i r
ne i ghbor s. Ea c h r out i ng t a bl e e nt r y ha s a r out e - t i me out t i me r
as s oc i a t e d wi t h i t. Whe n t he r out e- t i meout t i mer expi r es, t he r out e
i s ma r ke d i nva l i d but i s r e t a i ne d i n t he t a bl e unt i l t he r out e - flus h
t i me r e xpi r e s.
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I nt e rnat I onal J ournal of e l e ct ronI cs & communI cat I on t e chnol ogy
E. I nt er medi at e syst em- i net er medi at e syst em ( I S- I S) -
I nt e gr a t e d I nt e r me di a t e Sys t e m - I nt e r me di a t e Sys t e m r out i ng
pr ot oc ol i s a l i nk s t a t e pr ot oc ol s i mi l a r t o OSPF t ha t i s us e d wi t h
l a r ge e nt e r pr i s e a nd I SP c us t ome r s. An i nt e r me di a t e s ys t e m i s a
r out er and I S- I S i s t he r out i ng pr ot ocol t hat r out es packet s bet ween
i nt e r me di a t e s ys t e ms. I S- I S ut i l i z e s a l i nk s t a t e da t a ba s e a nd r uns
t he SPF Di j ks t r a al gor i t hm t o s el ect s hor t es t pat hs r out es. Nei ghbor
r out e r s on poi nt t o poi nt a nd poi nt t o mul t i poi nt l i nks e s t a bl i s h
a dj a c e nc i e s by s e ndi ng he l l o pa c ke t s a nd e xc ha ngi ng l i nk s t a t e
dat abas es. I S- I S r out er s on br oadcas t net wor ks s el ect a des i gnat ed
r out e r t ha t e s t a bl i s he s a dj a c e nc i e s wi t h a l l ne i ghbor r out e r s on
t ha t ne t wor k. The de s i gna t e d r out e r a nd e a c h ne i ghbor r out e r wi l l
e s t a bl i s h a n a dj a c e nc y wi t h a l l ne i ghbor r out e r s by mul t i c a s t i ng
l i nk s t a t e a dve r t i s e me nt s t o t he ne t wor k i t s e l f. Tha t i s di f f e r e nt
f r om OSPF, whi c h e s t a bl i s he s a dj a c e nc i e s be t we e n t he DR a nd
e a c h ne i ghbor r out e r onl y.
I S- I S us e a hi er ar chi cal ar ea s t r uct ur e wi t h l evel 1 and l evel 2 r out er
t ype s. Le ve l 1 r out e r i s s i mi l a r t o OSPF i nt r a - a r e a r out e r s, whi c h
ha ve no di r e c t c onne c t i ons out s i de of i t s a r e a. Le ve l 2 r out e r s
compr i s e t he backbone ar ea whi ch connect s di f f er ent ar eas s i mi l ar
t o OSPF a r e a 0. Wi t h I S- I S a r out e r c a n be a n L1/L2 r out e r whi c h
i s l i ke a n OSPF a r e a bor de r r out e r ( ABR) whi c h ha s c onne c t i ons
wi t h i t s a r e a a nd t he ba c kbone a r e a. The di f f e r e nc e wi t h I S- I S i s
t ha t t he l i nks be t we e n r out e r s c ompr i s e t he a r e a bor de r s a nd not
t he r out e r. Ea c h I S- I S r out e r mus t ha ve a n a s s i gne d a ddr e s s t ha t i s
uni que f or t ha t r out i ng doma i n. An a ddr e s s f or ma t i s us e d whi c h
i s c ompr i s e d of a n a r e a I D a nd a s ys t e m I D. The a r e a I D i s t he
a s s i gne d a r e a numbe r a nd t he s ys t e m I D i s a MAC a ddr e s s f r om
one of t he r out e r i nt e r f a c e s. The r e i s s uppor t f or va r i a bl e l e ngt h
s ubne t ma s ks, whi c h i s s t a nda r d wi t h a l l l i nk s t a t e pr ot oc ol s. Not e
t ha t I S- I S a s s i gns t he r out i ng pr oc e s s t o a n i nt e r f a c e i ns t e a d of
a ne t wor k.
Cha r a c t e r i s t i c s of I S- I S-
I t i s Li nk s t a t e r out i ng pr ot oc ol•
I t s uppor t s Va r i a bl e l e ngt h s ubne t ma s ki ng•
Rout i ng Adve r t i s e me nt s a r e Pa r t i a l l y s e nt Whe n Rout i ng •
Cha nge s Oc c ur.
Loa d Ba l a nc i ng oc c ur s Ac r os s 6 Equa l Cos t Pa t hs.•
He l l o t i me r i nt e r va l i s 10 s e c onds.•
De a d t i me r i nt e r va l i s 30 s e c onds.•
I t us e s a r e a s a s Hi e r a r c hi c a l t opol ogy s i mi l a r t o OSPF.•
De s i gna t e d r out e r e l e c t i on i s done but no BDR i s e l e c t e d. •
[ 8]
I I I. Compar i son Bet ween RI P, I GRP, EI GRP, OSPF and
I S- I S-
Th e c o mp a r i s o n o f d i f f e r e n t I n t e r i o r g a t e wa y p r o t o c o l s i s
s umma r i z e d be l ow.
Ta bl e 1: Shows Compa r i s on Be t we e n Di f f e r e nt I GP Pr ot oc ol s
Rout i ng
pr ot oc ol
AD Me t r i c
Pe r i odi c
upda t e s
Tr i gge r i ng
upda t e s
Pa r t i a l
upda t e s
Vl s m/c i dr
s ubne t
ma s k
Ri p v1 120 Hop c ount Ye s ye s No No
Ri pv2 120 Hop c ount Ye s ye s No ye s
os pf 110
Cos t
Ba ndwi dt h
No ye s ye s ye s
i gr p 100 Ba ndwi dt hNo ye s ye s ye s
e i gr p 90
Ba ndwi dt h,
Loa d
de l a y ,
Re l i a bi l i t y
No ye s ye s ye s
I S- I S 115
Cos t ,
Ba ndwi dt h
No ye s ye s ye s
I V. Concl usi on
Thi s pa pe r c onc l ude s t he di f f e r e nt I nt e r i or ga t e wa y pr ot oc ol s
( I GP) a nd we e xpl a i ne d e ve r y pr ot oc ol br i e fly a nd quot e d s ome
i mpor t ant char act er i s t i cs of t he pr ot ocol s whi ch wi l l hel p t o deci de
t he us e of pr ot oc ol i n t he ne t wor k a c c or di ng t o t he ne t wor k s i z e
a nd s pe e d of t he ne t wor k.
Ref er ences
[ 1] Vi s h a l s h a r ma, Ra j n e e s h Na r u l a a n d Sa me e r k h u l l a r
“ Pe r f or ma nc e Ana l ys i s of I EEE 802.3 us i ng I GRP a nd
EI GRP Rout i ng Pr ot ocol s ” I nt er nat i onal J our nal of Comput er
Appl i c a t i ons ( 0975 – 8887) Vol ume 44– No13, Apr i l 2012
[ 2] I t t i phon kr i npayor m and Suwat Pat t ar amal ai,”Li nk Recover y
Co mp a r i s o n Be t we e n OSPF & EI GRP “, I n t e r n a t i o n a l
Conf er ence on I nf or mat i on and Comput er Net wor ks ( I CI CN
2012) I PCSI T vol. 27 ( 2012) I ACSI T Pr e s s, Si nga por e
[ 3] Re t a n a, A., Wh i t e, R., Sl i c e, D. CCI E Pr o f e s s i o n a l
De ve l opme nt: Adva nc e d I P Ne t wor k De s i gn. Ci s c o Pr e s s,
1999.
[ 4] Todd La mml e, Ci s c o Ce r t i fie d Ne t wor k As s oc i a t e, St udy
Gui de 5t h Edi t i on
[ 5] J ohn Moy “ OSPF pr ot oc ol a na l ys i s ”, r f c 1245, J ul y 1991.
[ 6] h t t p://www.c i s c o.c o m/p a r t n e r/s d m/c i/r o u t i n g/o s p f/CI _
OSPF.ht ml ( 48 of 48) [ 10/11/2001 5:34:44 PM]
[ 7] ht t p://www.c i s c o.c om/pa r t ne r/s dm/c i/r out i ng/Ri p/CI _RI P.
ht ml
[ 8] St ude nt gui de,“ Configur i ng I S- I S pr ot oc ol ”, ve r s i on1.2-
modul e 7.