Rahul Khadse
IP Routing
When we want to connect two or more networks using different n/w addresses then we have to use IP Routing technique. The router will be used to perform routing between the networks. A router will perform following functions for routing.
Steps to perform static routing
(1) Create a list of all n/w present in internetwork.
Static Routing Example: -
Advantages of static routing
Disadvantages of static routing
Alternate command to specify static route
Backup route or loading static route
If more than one path are available from our router to
destination then we can specify one route as primary and other route as backup
route. Administrator Distance is used to specify one
route as primary and other route as backup. Router will select lower AD route to
forward the traffic. By default static route has AD value of 1. With backup path, we will
specify higher AD so that this route will be used if primary route is unavailable.
Default Routing
Default routing means a route for any n/w. these routes are specify with the help of following syntax: -
Dynamic Routing
Types of Dynamic Routing Protocols
According to the working there are two types of Dynamic Routing Protocols.
Autonomous
system
Protocols
Operation: -
Bandwidth Consumption
The problem of accessive bandwidth consumption is solved out with the help of autonomous system. It exchanges b/w different routers. We can also perform route summarization to reduce the traffic.
Routing Loops
It may occur b/w adjacent routers due to wrong routing information. Distance Vector routing is also called routing by Rumor. Due to this the packet may enter in the loop condition until their TTL is expired.
Method to solve routing loops
There are five different methods to solve or reduce the problem of routing loop.
When we want to connect two or more networks using different n/w addresses then we have to use IP Routing technique. The router will be used to perform routing between the networks. A router will perform following functions for routing.
(1) Path
determination
(2) Packet
forwarding
(1) Path determination
The
process of obtaining path in routing table is called path determination. There
are three different methods to which router can
learn path.
i) Automatic detection of directly connected n/w.
ii) Static & Default routing
iii) Dynamic routing
(2) Packet forwarding
It is a
process that is by default enable in router. The router will perform packet forwarding only if route is available in the
routing table.
Routing Process
(i) The pc has a packet in which destination address
is not same as the local n/w address.
(ii)
The pc will send an ARP request for default gateway. The router will reply to
the ARP address and inform its Mac address to pc.
(iii)
The pc will encapsulate data, in which source IP is pc itself, destination IP
is server, source Mac is pc’s LAN interface and destination
Mac is router’s LAN interface.
S. MAC D. MAC
PC1 R1
Destination. IP 172.16.0.5
Source. IP 10.0.0.6
The router will receive the frame, store it into
the buffer. When obtain packet from the frame then forward data according to the
destination IP of packet. The router will obtain a route from routing table according to which next
hop IP and interface is selected .
(iv) According
to the next hop, the packet will encapsulated with new frame and data is send to the output queue of the interface.
Static Routing
In this routing, we have to use IP route commands
through which we can specify routes for different networks. The administrator will
analyze whole internetwork topology and then specify the route for each n/w that is not
directly connected to the router.Steps to perform static routing
(1) Create a list of all n/w present in internetwork.
(2) Remove the n/w address from list, which is directly
connected to n/w.
(3) Specify each route for each routing n/w by using IP
route command.
Router(config)#ip route <destination n/w>
<mask> <next hop ip>
Next hop IP it
is the IP address of neighbor router that is directly connected our router.
Static Routing Example: -
Router#conf ter
Router(config)#ip route 10.0.0.0 255.0.0.0
192.168.10.2Advantages of static routing
(1) Fast and efficient.
(2) More control over selected path.
(3) Less overhead for router.
(4) Bandwidth of interfaces is not consumed in routing
updates.Disadvantages of static routing
(1) More overheads on administrator.
(2) Load balancing is not easily possible.
(3) In case of topology change routing table has to be
change manuallyAlternate command to specify static route
Static route can also specify in following syntax: -
Router(config)#ip route 172.16.0.0 255.255.0.0 172.25.0.2
Or
Router(config)#ip route 172.16.0.0 255.255.0.0 serial
0Backup route or loading static route
Protocols AD
Directly Connected 0
Static 1
BGP 20
EIGRP 90
IGRP 100
OSPF 110
RIP 120
Syntax: - To set backup path
Router(config)#ip route <dest. n/w> <mask>
<next hop> <AD>
Or
<exit
interface>
Example: -
Router#conf ter
Example: -
Router#conf ter
Router(config)#ip route 150.10.0.0 255.255.0.0 150.20.0.5
Router(config)#ip route 150.10.0.0 25.255.0.0 160.20.1.1 8
(below 20)
Router(config)#exitDefault Routing
Default routing means a route for any n/w. these routes are specify with the help of following syntax: -
Router(config)#ip route 0.0.0.0 0.0.0.0 <next hop>
Or
<exit
interface>
This type of routing is used in below diagramDia 1 - Stub network :- A n/w which has only one exit interface is called stub network.
 |
| If there is one next hop then we can use default routing |
Dia 2 - Internet connectivity :- On Internet, million of n/ws are present. So we
have to specify default routing on our router. Default route is also called gateway of last
resort. This route will be used when no other routing protocol is used.
Router(config)#ip route 10.0.0.0 255.0.0.0 172.16.0.5
Router(config)#ip route 0.0.0.0 0.0.0.0 200.100.100.11
To display routing table --> Router#sh ip route
To display static routes only --> Router#sh ip route static
To display routing table --> Router#sh ip route
To display static routes only --> Router#sh ip route static
S 192.168.10.0/28 [1/0] via 172.16.0.
To display connected n/ws only -->
To check all the interface of a router --> Router#sh interface brief
To display connected n/ws only -->
To check all the interface of a router --> Router#sh interface brief
Dynamic Routing
Types of Dynamic Routing Protocols
According to the working there are two types of Dynamic Routing Protocols.
(1) Distance Vector
(2) Link
State
According to the type of area in which protocol is used
there are again two types of protocol: -
(1) Interior Routing Protocol
(2) Exterior Routing Protocol
Autonomous system is the group of contiguous routers
and n/w, which will share their routing information directly with each other. If
all routers are in single domain and they share their information directly with each other
then the size of routing updates will depend on the no. of n/w present in the
Internetwork. Update for each n/w may take 150 – 200 bytes information.
For example: - if there are 1000 n/ws then size of update
will be
200*1000
= 200000 bytes
The routing information is send periodically so
it may consume a large amount of bandwidth in our network.
Interior Routing Exterior
Routing
RIP BGP
IGRP EXEIGRP
EIGRP
OSPF
Distance Vector Routing
The Routing, which is based on two parameters, that is
distance and direction is called Distance Vector Routing. The example of Distance
Vector Routing is RIP & IGRP.
Operation: -
(1) Each Router will send its directly connected
information to the neighbor router. This information is send periodically to the
neighbors.
(2) The neighbor will receive routing updates
and process the route according to following conditions.
(i) If update of a new n/w is received then this information
is stored in routing table.
(ii) If
update of a route is received which is already present in routing table then
route will be refresh that is route times is reset to
zero.
(iii) If update is received for a route with
lower metric then the route, which is already present in our routing table. The router will
discard old route and write the new route in the routing table
(iv) If update is received with higher metric
then the route that is already present in routing table , in thae case the new update will discard.
3) A timer is associated with each route. The
router will forward routing information on all interfaces and entire routing table is send
to the neighbor. There are three types of timers associated with routes.
(i) Route update timer
It is the time after which the router will
send periodic update to the neighbor.
(ii) Route
invalid timer
It is the time
after which the route is declared invalid, if there are no updates for the route. Invalid route are not forwarded to neighbor
routers but it is still used to forward the traffic.
(iii) Route
flush timer
It is
the time after which route is removed from the routing table, if there are no updates about the router .
Metric of Dynamic Routing
Metric are the measuring unit to calculate the
distance of destination n/w. A protocol ma use a one or more than one at a time to
calculate the distance. Different types of metric are :-
(1) Hop Count
(2) Band Width
(3) Load
(4) Reliability
(5) Delay
(6) MTU
Hop Count :-- It is the no. of Hops (Routers) a packet has to travel for a
destination n/w.
Bandwidth :-- Bandwidth is the speed of link. The path with higher
bandwidth is preferred to send the data.
Load :-- Load is the amount of traffic present in the interface. Paths with lower load and high.
Reliability :-- Reliability is up time of interface over a period of time.
Delay :-- Delay is the time period b/w a packet is sent and received by the destination.
MTU : -- It is the maximum size of packet that can be sent in a frame mostly MTU is set to 1500.
Problems of Distance Vector
There are two main problems of distance vector routing
Load :-- Load is the amount of traffic present in the interface. Paths with lower load and high.
Reliability :-- Reliability is up time of interface over a period of time.
Delay :-- Delay is the time period b/w a packet is sent and received by the destination.
MTU : -- It is the maximum size of packet that can be sent in a frame mostly MTU is set to 1500.
Problems of Distance Vector
There are two main problems of distance vector routing
(1) Bandwidth
Consumption
(2) Routing
Loops
Bandwidth Consumption
The problem of accessive bandwidth consumption is solved out with the help of autonomous system. It exchanges b/w different routers. We can also perform route summarization to reduce the traffic.
Routing Loops
It may occur b/w adjacent routers due to wrong routing information. Distance Vector routing is also called routing by Rumor. Due to this the packet may enter in the loop condition until their TTL is expired.
Method to solve routing loops
There are five different methods to solve or reduce the problem of routing loop.
(1) Maximum
Hop Count
(2) Flash
Updates/Triggered Updates
(3) Split Horizon
(4) Poison
Reverse
(5) Hold
Down
Maximum Hop Count :-- This method limits the maximum no. of hops a packet
can travel. This method does not solve loop problem. But it reduce the loop size
in the n/w. Due to this method the end to end size of a n/w is also limited.
Flash Updates/Triggered Updates :-- In this method a partial update is send to the all neighbors as soon as there is topology change. The router, which receives flash updates, will also send the flash updates to the neighbor routers.
Split
Horizon :-- Split Horizon states a route that update receive from
an interface can not be send back to same interface.
Poison Reverse :-- This method is the combination of split Horizon and Flash updates. It implements the rule that information received from the interface can not be sent back to the interface and in case of topology change flash updates will be send to the neighbor.
Hold Down :-- If a route changes frequently then the route is declared in Hold Down state and no updates are received until the Hold Down timer expires.
Flash Updates/Triggered Updates :-- In this method a partial update is send to the all neighbors as soon as there is topology change. The router, which receives flash updates, will also send the flash updates to the neighbor routers.
Poison Reverse :-- This method is the combination of split Horizon and Flash updates. It implements the rule that information received from the interface can not be sent back to the interface and in case of topology change flash updates will be send to the neighbor.
Hold Down :-- If a route changes frequently then the route is declared in Hold Down state and no updates are received until the Hold Down timer expires.
