Download Types of Routing Protocols

IP ROUTING PROTOCOL
1. INTRODUCTION
I’m going to discuss the IP routing process. This is an important subject to understand
since it certain to all routers and configurations that use IP.IP routing is the process of
moving packets from one network to another network using routers. And as before, by
routers I mean Cisco routers. You must understand the differences between a routing
protocol and a routed protocol .A routing protocol is used by routers to dynamically
find all the networks in the internetwork and to ensure that all routers have the same
routing table. Basically a routing protocol determines the path of a packet through an
internetwork. Examples of routing protocol are RIP, RIPV2, EIGRP and OSPF. Once
all routers know about all networks, a routed protocol can be used to send user data
(packet) through the established enterprise. Routed protocols are assigned to an
interface and determine the method of packet delivery. Examples of routed protocols
are IP and Ipv6.
Enhanced interior gateway routing protocol (EIGRP) is a proprietary Cisco protocol
that runs on Cisco routers. It is important for you to understand EIGRP because it is
probably one of the two most popular routing protocols in use today. I’m also going to
introduce you to the Open Shortest path first (OSPF) routing protocol, which is the
other popular routing protocol in use today.
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What is the function of the network layer in th OSI model?
Path determination, for traffic going through a network cloud, occurs at the network
layer (Layer 3). The path determination function enables a router to evaluate the
available paths to a destination and to establish the preferred handling of a packet. The
network layer provides best-effort end-to-end packet delivery across interconnected
networks. The network layer uses the IP routing table to send packets from the source
network to the destination network. After the router determines which path to use, it
proceeds with forwarding the packet. It takes the packet that it accepted on one interface
and forwards it to another interface or port that reflects the best path to the packet's
destination. A router generally relays a packet from one data link to another, using two
basic functions:
1. a path determination function - Routing
2. a switching function – Packet Forwarding
The path determination function enables the router to select the most appropriate
interface for forwarding a packet. The switching function allows a router to accept a
packet on one interface and forward it through a second interface.
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Packet: IP Source and IP Destination (Network Layer) addresses do not change. Data
Link Source and Data Link Destination addresses do change to reflect the current and
next hop routers. The routing table (coming) contains the IP address of the next-hop
router – This address is used to find the Data Link Destination address which is used to
encapsulate the original IP packet. The router’s path determination function looks up
the network address in the routing table and determines which interface it should exit.
The router’s switching function encapsulates it in the proper data link frame with the
proper data link destination address.
Routing vs. Routed
Routing
It is a technique or process that is used by router to select the best IP route to reach a
network.
Routing protocols are used between routers to: Determine the path of a packet through a
network. Maintain routing tables.
Examples: IGP and EGP
Routed protocols are: Assigned to an interface Once the path is determined by the
Routing protocol, determines method of delivery.
Examples: IP, IPX,Apple talk.
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Interior gate way Protocol & Exterior gate way Protocol
Autonomous system
AS stands for the autonomous system. Autonomous system may be defined as a
network under the same administration with a common routing policy.
IGP (Interior Gateway Protocol)
In case of the IGP all router with same Autonomous Number will share the same
routing table info or communication with each other. Autonomous Number is a number
that represents an area it can be any number in the range of 1-65535 IGRP (Interior
Gateway Routing Protocol) , EIGRP , OSPF
IGP – Routing protocols used within an AS
EGP (Exterior Gateway Protocol)
EGP – Routing protocols used between AS’s
it allows router with different AS number to communicate with each others for example
i) BGP (Border Gateway Protocol)
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Classful routing and classless routing overview
Classful Routing:
Classful routing protocols do not include the subnet mask with the route advertisement.
=>Within the same network, consistency of the subnet masks is assumed.
=>Summary routes are exchanged between foreign networks.
=>Examples of classful routing protocols:
i) RIP Version 1 (RIPv1)
ii) IGRP
Classless Routing:
Classless routing protocols include the subnet mask with the route advertisement.
=>Classless routing protocols support variable-length subnet masking (VLSM).
=>Summary routes can be manually controlled within the network.
=>Examples of classless routing protocols:
i) RIP Version 2 (RIPv2)
ii) EIGRP
iii) OSPF
iv) IS-IS
Administrative distance
It is a metric that rates the trustworthiness and reliability of the routing information
update being received either statically or dynamically. It can be any value in the range
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of 0-255 where 0 is most reliable and 255 is never ever used variable
=>Administrative distance for the directly connected networks 0
=>Administrative distance for the default and static routing is 1
=>Administrative distance for the EIGRP is 90
=>Administrative distance for the IGRP is 100
=>Administrative distance for the OSPF is 110
=>Administrative distance for the RIP is 120.
Types of Routing
Routing types
1) Static routing
2) Default routing
3) Dynamic routing
Static Routing:
In this type of routing we have to set the route manually. There is no any use of the
protocol in this type of the routing. This type of routing is suitable for small networks
and all the burden or responsibilities of performance of networks is on the network
administrators. Static routing is done on directly connected devices static routing is
more reliable. To manually set the entry we use the command as
Router # IP route destination network subnet mask exit interface or hop address
(administrative distance) (permanent)
Note recommend we have to use the next hop ip address.
Here administrative distance and permanent are the optional entries.
IP Route The command used to create the static route.
Destination-network The network you’re placing in the routing table.
Mask The subnet mask being used on the network.
Next-hop-address The address of the next-hop router that will receive the packet and
forward it to the remote network. This is a router interface that’s on a directly connected
network.
Exit-interface You can use it in place of the next-hop address if you want, but it’s got
to be on a point-to-point link, such as a WAN
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Administrative distance By default, static routes have an administrative distance of 1
(or even 0 if you use an exit interface instead of a next-hop address.
Directly Connected Networks and the IP Routing Table
192.168.2.0/24
e0
172.16.0.0/16
RTA
.1
s0
s0
.1
.2
192.168.1.0/24
RTB
10.0.0.0/8
s1
s1
.1
.2
RTC
e0
.1
RTA#show ip route
Codes: C - connected,.. <Other codes and gateway information omitted>
C
172.16.0.0/16 is directly connected, Serial0
C
192.168.2.0/24 is directly connected, Ethernet0
RTB#show ip route
Codes: C - connected,.. <Other codes and gateway information omitted>
C
172.16.0.0/16 is directly connected, Serial0
C
192.168.1.0/24 is directly connected, Serial1
RTC#show ip route
Codes: C - connected,.. <Other codes and gateway information omitted>
C
10.0.0.0/8 is directly connected, Ethernet0
C
192.168.1.0/24 is directly connected, Serial1
The Routing Tables
Notice that the routers only know about their own directly connected networks.
They are not sharing routing information because we have not configured any static
routes or dynamic routing protocols.
Directly Connected Networks and the IP Routing Table
192.168.2.0/24
e0
172.16.0.0/16
RTA
.1
s0
s0
.1
.2
192.168.1.0/24
RTB
10.1.0.0/16
s1
s1
.1
.2
RTC
e0
.1
RTA#show ip route
C
172.16.0.0/16 is directly connected, Serial0
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C
192.168.2.0/24 is directly connected, Ethernet0
RTA#ping 172.16.0.1
Sending 5, 100-byte ICMP Echos to 172.16.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms
RTA#ping 172.16.0.2
!!!!!
RTA#ping 192.168.1.1
.....
RTA#ping 192.168.1.2
.....
RTA#ping 10.1.0.1
Routing – Only directly connected hosts (routers) Routers can only reach networks
known about in its own routing table.
Configuring Static Routes
192.168.2.0/24
e0
172.16.0.0/16
RTA
.1
s0
s0
.1
.2
192.168.1.0/24
RTB
10.1.0.0/16
s1
s1
.1
.2
RTC
e0
.1
RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2
Network/subnet route
Intermediate Address (usuallynexthop)
RTA#show ip route
Codes: C - connected, S - static,
C
172.16.0.0/16 is directly connected, Serial0
S
192.168.1.0/24 [1/0] via 172.16.0.2
C
192.168.2.0/24 is directly connected, Ethernet0
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Default Routes
Default routing:
This routing is performing only on the stub networks. Stub networks are defined over
the networks which has only one exit interface.
This route allows the stub network to reach all known networks beyond router A.
Default routes are used to route packets with destinations that do not match any of the
other routes in the routing table. A default route is actually a special static route that
uses this format:
Syntax # ip route 0.0.0.0 0.0.0.0 exit interface /next hop address
In case of the default routing we have to assign any single ip over the stub router ie the
number of route entry are reduced to minimum
The default route is the IP address of the next hop when no other routes are
known.
To configure the default route to be 192.168.1.1:
config t
ip route 0.0.0.0 0.0.0.0 192.168.1.1
An interface can be used as an alternative to and IP address. To use serial0/0 for
destinations not in the routing table, use:
ip route 0.0.0.0 0.0.0.0 serial 0/0
Dynamic routing:
In case of dynamic routing a specific routing protocol is used and as a result router’s
routing table is configured. i.e. updated automatically. We need the highly sophisticated
router and thus the cost of routing is very high More suitable for the large networks
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Types of Routing Protocols
Distance Vector
 RIP V1
 IGRP
 RIP V2
Link state
 OSPF
Hybrid
 EIGRP
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When all routers in an internetwork are operating with the same knowledge, the
internetwork is said to have converged. Fast convergence is a desirable network feature
because it reduces the period of time in which routers would continue to make
incorrect/wasteful routing decisions.
Types of Routing Protocols
Three categories for the routing protocol:
Distance Vector Routing Protocol (DVRP )
Link State Routing Protocol (LSRP)
Hybrid Routing Protocol (HRP)
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Distance vector
Distance Vector Routing Protocol (DVRP)
In case of DVRP every router sends its complete routing table as an update to its
immediate neighbors The metric used to identify the best route is HOP count
Examples are
RIP (Routing Information Protocol)
IGRP (Interior Gateway Routing Protocol )
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Distance Vector Routing Protocol
Its known as DVRP protocol In case of DVRP each router send its complete routing
table as an update to its immediate neighbors The metric used to identify the best route
is HOP count. Lower the metric , best the route is Routing through DVRP is also called
routing by rumors. Pin hole congestion
i) When all possible routes to reach the destination network has equal metric. This
problem is known as pin hole congestion
ii) To solve this problem load balancing is done.
=> Slow convergence is there in case of DVRP
=> Loop count up till infinite
Loop avoidance
Maximum hop count
1) Max hop count (means that how many router are there in the networks)
ii) RIP 15
ii) EIGRP 100 by default 255 max
iii) IGRP 100 by default 255 max
iv) OSPF infinity
2)The maximum hop count will control how long it takes for a routing table entry to
become invalid
Split horizon
1)The route over which an update is being received , no new update will be send or
transfer over that route.
2)Split horizon with poison reverse
3)It is never useful to send information about a route back in the direction from which
the original information came.
Trigger update
1) The update is sent immediately the happening
2) It does not wait for timer
Hold down timer
1) In case of RIP it will wait for 180 secs waiting for valid update and after expiry of
hold down timer it will forward update that network is down
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Example: RIP (Router Information Protocol)
It is a DVRP protocol, in case of which each router sends its complete routing table to
its immediate neighbor. The metric used to identify the best route is HOP counts lower
the metric better the route.
=> Administrative distance is 120
=> Maximum HOP count is 15.
=> There are two versions of the RIP protocol
RIP V1 (version 1)
RIP V2 (version 2)
Timer
Update Timer
It is a time period after the expiry of which each router sends its complete routing table
as an update to its immediate router.
It is by default is 30 sec
Invalid Timer
If no new update is received regarding a specific router entry the time period for which
that route entry will be hold waiting for a valid update is called invalid timer
It is by default 180 second.
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Hold down timer
If a route update is received regarding a specific route entry, that route entry has
become unreachable then the time period for which the route entry will be held waiting
for the valid update is called hold down time.
It is by default 180 second
Flush out timer
Once a route entry has become invalid the time period within which router will intimate
all its immediate neighbors regarding the same is called flush out timer
It is by default is 240 seconds.
Example: IGRP
=> Interior Gateway Routing Protocol
=> It is a DVRP (Distance Vector Routing Protocol)
=> Administrative distance is 100
=> It is a Cisco proprietary routing protocol which mean it can work only on Cisco
enables devices.
=> The max HOP count is 255
=> By default HOP is 100
=> It uses the concept of autonomous system number
=> It is a classful routing protocol
=> It does not support VLSM
=> The metric used to identify the best path is combination of two thing
1) Bandwidth &
2) Delay
=> Timer
Update time 90 seconds (by default)
Invalid timer 3* update timer =270 seconds
Hold down timer 3* update timer + 10 =280
Flush out timer 7* update timer =630 seconds
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Hybrid Routing Protocol
=> Its combine the feature of both DVRP and LSRP protocol
=> Examples are
EIGRP (Enhance Interior Gateway Routing Protocol)
Example: EIGRP (Enhance Interior Gateway Routing Protocol)
=> It is a hybrid routing protocol that combines the feature of the link state routing
protocol and distance vector routing protocol.
=> Administrative distance 90
=> It uses the concept of the autonomous number
=> It is a Cisco proprietary routing protocol.
=> It is a classless routing protocol
=> It support the VLSM
=> Maximum HOP count limit is 255
=> By default it is 100
=> It uses IP protocol 88.
Characteristic of the EIGRP
=> PDM
1) Protocol dependent Module
i) EIGRP provide support for multiple network layer protocol IP, IPX,
APPLETALK through PDM.
ii) For each protocol an independent set of database will be created. I.e. if IP is
used then IP/EIGRP database, if IPX then IPX/EIGRP database, if AppleTalk then
AppleTalk /EIGRP.
=> Efficient neighbor discovery
1) Hello packets are exchanged
2) AS number should be same
3) Metric should be identical
=> When two routers become immediate neighbor then only for the first time they will
exchange their complete routing table with each other and then only the route updates
will be sent at regular interval of time.
Point to remember
=> the best route to reach the destination network is called feasible distance
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=> the second best alternate route also called the backup route or feasible successor
=> All possible routes to reach the destination network as reported by the immediate
neighbor are called reported distances.
=> Communication via RTP
1) Reliable Transport Protocol
2) For the first time the router send the multicast hello to its immediate neighbor
then it check the list of all the routers that have not replied to that multicast hello.
3) With them it will start unicast hello for next 16 times and even if there is no any
reply then that router will be declared as dead.
=> DUAL
1) Defusing Update Algorithm
2) It is used to identify
i) The best route to reach the destination network called feasible distance
ii) The second best route called feasible successor
Metric
=> The metric used to identify the best route is combination of 4 things
1) Bandwidth
2) Delay
3) Load
4) Reliability
=> Three table are prepared
1) Neighborship table
2) Topology table
3) Routing table
=> EIGRP provide support for the larger networks
1) It is a classless protocol
2) It supports VLSM
3) The max HOP count is 255 by default it is 100
4) EIGRP supports multiple autonomous system number.
=> EIGRP support the auto summarize
=> Eigrp metric is the same as IGRP*256, It uses the smallest B.W, Reliablity, Load &
MTU with the Cumulative delay upon the path…..The MTU doesn’t actually used in
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the Metric calculations, But is included in the EIGRP Routing updates.
=> Potential routing protocol for the core of a network; used in large networks.
=> For neighbor relation to be established, both routers must send and receive Hello or
Ack packets from each other, they must have the same AS #, and the same Metric K
values.
=> Eigrp doesn’t restrict that neighbors must have the same Hello & dead interval
timers, Unlike OSPF.
Link State Routing Protocol (LSRP)
=> In case of LSRP when two router become immediate neighbor then only for the first
time they will exchange their complete routing table with its immediate neighbor and
then only the link status message will be send
=> There are three table are created
i) Neighbourship table
ii) Topology table
iii) Routing table
=> Example
OSPF (Open Shortest Path First)
Example: OSPF(Open Shortest Path First)
=> it is a link state routing protocol
=> its AD =110
=> HOP count limit is unlimited
=> It is an open standard routing protocol that provide multi vendor support
=> It is classless routing protocol
=> It supports VLSM
=> The metric used to identify the best route is bandwidth by default (10^8 / BW in
bps)
=> It uses the concept of AS number and Area
=> Sends partial route updates only when there are changes.
=> Send hello packets every 10 sec with dead timer of 40 sec over P-P & BC networks.
=> Send hello packets every 30 sec with dead timer of 120 sec over NBMA networks.
=> For 2 routers to be adjacent:
1st. Hello packets must be sent & received.
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2nd They must have the same hello & dead timers
Also & same Net ID with subnet mask.
3rd They must be in the same area.
Benefit of hierarchical architecture of OSPF
i) Confine network instability only to a part of a network
ii) Reduced routing overhead
iii) Scalability and flexibility
Terms in the OSPF
Area
Each AS no. divided into smaller parts and each such part is known as an area
Area 0
The main area or the backbone area that manages the overall process of communication
is called area 0.
ABR (Area Border Router)
It allows two diff. area routers to communication with each other with in the same AS
no.
ASBR (Autonomous System Border Router)
It allows two different autonomous system routers to communication with each other
OSPF is based on dijkestra algorithm in case of which first
i) The shortest path tree is created and then
ii) The best route to reach destination network is identification
Basic terminology
Link:
It represents an interconnection between two devices or an interface whose status can be
either up or down
Router ID:
It is a metric in terms of highest IP address S0 router with the highest IP address or
router ID will be elected as designated router (DR)
Neighbor:
Router which are adjacent to each other are said to be neighbors.
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Adjacency:
Router which are immediate neighbor to each others are said to be adjacent
Hello packet:
It is only through exchange of hello packet two router will become neighbor to each
other
Link state advertisement:
It contains information regarding the status of the link and the route update
Designated router (D R):
Router with the highest IP address or router is will be elected as the designation router
Backup designated router (BDR):
Router with second highest router ID or IP address will be elected as BDR.
Neighbors:
Routers that share a common segment become neighbors on that segment. Neighbors
are elected via the Hello protocol. Hello packets are sent periodically out of each
interface using IP multicast. Routers become neighbors as soon as they see themselves
listed in the neighbor's Hello packet. This way, a two way communication is
guaranteed. Two routers will not become neighbors unless they agree on the following:
Area-id:
Two routers having a common segment; their interfaces have to belong to the same area
on that segment. Of course, the interfaces should belong to the same subnet and have a
similar mask.
Authentication:
OSPF allows for the configuration of a password for a specific area. Routers that want
to become neighbors have to exchange the same password on a particular segment.
Hello and Dead Intervals:
OSPF exchanges Hello packets on each segment. This is a form of keep alive used by
routers in order to acknowledge their existence on a segment and in order to elect a
designated router (DR) on multi access segments. The Hello interval specifies the
length of time, in seconds, between the hello packets that a router sends on an OSPF
interface. The dead interval is the number of seconds that a router's Hello packets have
not been seen before its neighbors declare the OSPF router down. OSPF requires these
intervals to be exactly the same between two neighbors. If any of these intervals are
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different, these routers will not become neighbors on a particular segment. The router
interface commands used to set these timers are: ip ospf hello-interval seconds and ip
ospf dead-interval seconds.
Stub area flag:
Two routers have to also agree on the stub area flag in the Hello packets in order to
become neighbors. Stub areas will be discussed in a later section. Keep in mind for now
that defining stub areas will affect the neighbor election process.
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Conclusion
IP routing protocols have tunable parameters that operators can set to control the flow of
traffic through their networks. Optimization based on local-search techniques plays an
important role in adapting these parameters to the prevailing network conditions. In this
chapter, we considered three variants of the optimization problem, with increasing
complexity:
1. When each destination connects to the network at a single location, the optimization
problem consists of setting the link weights that drive how the routers direct traffic on
shortest paths. The inputs to the optimization problem are the traffic matrix and the
capacitated network topology.
2. When some destinations are reachable via multiple egress points, the optimization
problem becomes more complicated. Instead of the traffic matrix, the offered load is
represented as a set of traffic demands the volume of traffic entering at a certain router and
traveling to a particular destination. The optimization problem must also consider the set
of egress points for each destination prefix.
Logically-centralized control over path selection: The routing protocols in today’s IP
networks were designed, first and foremost, to be implemented in a distributed fashion.
More recently, the increasing capabilities of computers makes it possible to select the
paths for a large collection of routers in a separate platform with a network-wide view of
the topology and traffic. Rather than emulating today’s distributed protocols, these
platforms could define new frameworks for computing paths in a logically-centralized
fashion to satisfy network engineering goals directly.
Explicit negotiation between neighboring domains: When a configuration change
causes a router to direct traffic to a different egress point, the neighboring domain starts
receiving traffic at a different ingress point.
Logically-centralized control over path selection: The routing protocols in today’s IP
networks were designed, first and foremost, to be implemented in a distributed fashion.
More recently, the increasing capabilities of computers makes it possible to select the
paths for a large collection of routers in a separate platform with a network-wide view of
the topology and traffic Rather than emulating today’s distributed protocols, these
platforms could define new frameworks for computing paths in a logically-centralized
fashion to satisfy network engineering goals directly.
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Designing new IP routing architectures that are more amenable to optimization is a
promising avenue for future research.
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