ROUTING The process of transferring data from one local area network to
another network.
Layer 3 devices (Network Layer)
Routed protocol Enables to forward packet from one router to another for example IP, IPX
Routing protocol sends and receives routing information packets to and from other routers for example RIP, OSPF, IGRP
Routing protocols gather and share the routing information used to maintain and update routing tables.
That routing information is in turn used to route a routed protocol to its final destination
WHAT IS ROUTING?
To route, a router needs to know: Destination addresses Sources it can learn from Possible routes Best route
172.16.1.010.120.2.0
WHAT IS ROUTING? (CONT.)WHAT IS ROUTING? (CONT.)
NetworkProtocol
DestinationNetwork
ConnectedLearned
10.120.2.0172.16.1.0
Exit Interface
E0S0 Routed Protocol: IP
Routers must learn destinations that are not directly connected
172.16.1.010.120.2.0
E0S0
ROUTE TYPES
Static routing - network administrator configures information about remote networks manually. They are used to reduce overhead and for security.
Dynamic routing - information is learned from other routers, and routing protocols adjust routes automatically.
Because of the extra administrative requirements, static routing does not have the scalability of dynamic routing.
IP ROUTING The different types of routing are:
Static routing Default routing Dynamic routing
STATIC ROUTES Benefits
No overhead on the router CPU No bandwidth usage between routers Adds security
Disadvantage Administrator must really understand the internetwork If a network is added to the internetwork, the
administrator has to add a route to it on all routers Not feasible in large networks
STATIC ROUTE CONFIGURATION
S0 S0E010.0.0.1
10.0.0.2
30.0.0.220.0.0.120.0.0.2 30.0.0.1
A
S0
E0
40.0.0.2
40.0.0.1
B
S1
R1# config tR1(config)#ip route 30.0.0.0 255.0.0.0 20.0.0.2R1(config)#ip route 40.0.0.0 255.0.0.0 20.0.0.2
R2# config tR2(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.1R2(config)#ip route 40.0.0.0 255.0.0.0 30.0.0.2
R3# config tR3(config)#ip route 10.0.0.0 255.0.0.0 30.0.0.1R3(config)#ip route 20.0.0.0 255.0.0.0 30.0.0.1
DEFAULT ROUTES Can only use default routing on stub networks Stub networks are those with only one exit path out of the
network The only routers that are considered to be in a stub
network are R1 and R3
S0 S0E010.0.0.1
10.0.0.2
30.0.0.220.0.0.120.0.0.2 30.0.0.1
A
S0
E0
40.0.0.2
40.0.0.1
B
S1
Stub Network
ip route 0.0.0.0 0.0.0.0 172.16.2.2 or S0
DEFAULT ROUTES
172.16.2.1
SO
172.16.1.0
B172.16.2.2
ISPA B
This route allows the stub network to reach all known networks beyond router A.
10.0.0.0
DEFAULT ROUTE CONFIGURATION
R1# config tR1(config)#ip route 0.0.0.0 0.0.0.0 20.0.0.2
R3# config tR3(config)#ip route 0.0.0.0 0.0.0.0 30.0.0.1
R2# config tR2(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.1R2(config)#ip route 40.0.0.0 255.0.0.0 30.0.0.2
S0 S0E010.0.0.1
10.0.0.2
30.0.0.220.0.0.120.0.0.2 30.0.0.1
A
S0
E0
40.0.0.2
40.0.0.1
B
S1
WHAT IS A ROUTING PROTOCOL?WHAT IS A ROUTING PROTOCOL?
Routing protocols are used between routers to determine paths and
maintain routing tables. Once the path is determined a router can route a routed protocol.
NetworkProtocol
DestinationNetwork
ConnectedRIPIGRP
10.120.2.0172.16.2.0172.17.3.0
Exit Interface
E0S0S1
Routed Protocol: IPRouting protocol: RIP, IGRP
172.17.3.0
172.16.1.010.120.2.0
E0S0
• An autonomous system is a collection of networks under a common administrative domain.
• AS parameter is 16-bit number for 0-65535
• Internet is a Public network and IANA gives every Carrier or ISP a unique AS no.
• Every carrier or ISP has its own responsibility to manage and maintain its own network.
• PTCL and Transworld are only two AS in Pakistan
• IGPs operate within an autonomous system, RIP, IGRP, EIGRP, OSPF, IS-IS
• EGPs connect different autonomous systems, BGP
AUTONOMOUS SYSTEMS: INTERIOR OR EXTERIOR ROUTING PROTOCOLS
TYPES OR CLASSES OF ROUTING PROTOCOLS
DISTANCE VECTOR:
• Exchange routing table between routers neighbors after periodic time interval for example RIP for 30sec and IGRP for 90 sec.
• Complete Routing table exchange.
• Distance vector routing protocol only have best path information to reach destination.
• No complete information of network topology, just knows the information of best path to reach destination.
• Bandwidth is not efficiently utilized.
• This is also know as routing by rumor
• Examples are RIP, RIPV2 and IGRP.
LINK STATE:
• Exchange routing updates not complete table, whenever there is some change in network topology.
• Have complete information of network topology.
• Bandwidth efficiently utilized.
• More accurate routing decisions.
• CPU and Memory intensive.
• Examples are OSPF and IS-IS.
TYPES OR CLASSES OF ROUTING PROTOCOLS
Distance Vector RIP V1 IGRP RIP V2
Link state OSPF IS-IS
Hybrid EIGRP
CLASSFUL ROUTING OVERVIEW
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.
Not Support VLSM
Examples of classful routing protocols: RIP Version 1 (RIPv1) IGRP
CLASSLESS ROUTING OVERVIEW
Classless routing protocols include the subnet mask with the route advertisement.
Classless routing protocols support variable-length subnet masking (VLSM) and subnetting
Examples of classless routing protocols: RIP Version 2 (RIPv2) EIGRP OSPF IS-IS
DISTANCE VECTOR ROUTING PROTOCOLS
Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors.
DISTANCE VECTOR
Uses Bellman Ford Algorithm It needs to find out the shortest path from one network to other There are two Distance Vector Protocol, Both uses different metric RIP – Hop count as metric IGRP – Uses composite Metric are bandwidth, Delay, Load,
Reliability and MTU
192.168.10.1
192.168.20.1
DISTANCE VECTOR
DV protocol are known as Routing by rumor RIP uses only Hop count RI routing table metric for 192.168.20.1 network will be
3 2
192.168.10.1
192.168.20.1
0
1
1
2
2
3R1
IGGRP uses bandwidth and delay as Metric RI routing table metric for 192.168.20.1 network will be
30 60
192.168.10.1
192.168.20.1
56 kbps
1 Mbps1 Mbps
1 Mbps
56 kbps
R110
10
10
30 30
DISTANCE VECTOR
SOURCES OF INFORMATION AND DISCOVERING ROUTES
Routers discover the best path to destinations from each neighbor.
INCONSISTENT ROUTING ENTRIES
Each node maintains the distance from itself to each possible destination network.
INCONSISTENT ROUTING ENTRIES (CONT.)
Slow convergence produces inconsistent routing.
• Router C concludes that the best path to network 10.4.0.0 is through router B.
INCONSISTENT ROUTING ENTRIES (CONT.)
• Router A updates its table to reflect the new but erroneous hop count.
INCONSISTENT ROUTING ENTRIES (CONT.)
• Packets for network 10.4.0.0 bounce (loop) between routers B and C.
ROUTING LOOPS
DEFINING A MAXIMUM HOP COUNT
Define a limit on the number of hops to prevent infinite loops.
One way of solving routing loop problem is to define a maximum hop count.
RIP permits a hop count of up to 15, so anything that requires 16 hops is deemed unreachable
SPLIT HORIZON
The split horizon technique attempts to eliminate routing loops and speed up convergence. The rule of split horizon is that it is never useful to send information about a route back in the direction from which the original packet came. In the example: Router C originally announced a route to network
10.4.0.0 to router B. It makes no sense for router B to announce to router C that router B has access to network 10.4.0.0 through router C.
SPLIT HORIZON
Solution to the Routing Loop problem
Split Horizon is a rule that routing information cannot be sent back in the direction from which it was received
Had split horizon been used in our example, Router B would not have included information about network 10.4.0.0 in its update to Router C.
ROUTE POISONING
Route Poisoning. Usually used in conjunction with split horizon
Route poisoning involves explicitly poisoning a routing table entry for an unreachable network
Once Router C learned that network 10.4.0.0 was unavailable it would have immediately poisoned the route to that network by setting its hop count to the routing protocol’s infinity value
In the case of RIP, that would mean a hop count of 16.
TRIGGERED UPDATES
oNew routing tables are sent to neighboring routers on a regular basis.
oRIP updates occur every 30 seconds
oHowever a triggered update is sent immediately in response to some change in the routing table.
oThe router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change.
oTriggered updates, used in conjunction with route poisoning, ensure that all routers know of failed routes.
TRIGGERED UPDATES GRAPHIC
RIP TIMERS Route update timer Sets the interval (typically 30
seconds) between periodic routing updates
Route invalid timer Determines the length of time (180 seconds) before a router determines that a route has become invalid
Holddown timer This sets the amount of time during which routing information is suppressed. This continues until either an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds
Route flush timer Sets the time between a route becoming invalid and its removal from the routing table (240 seconds).
ROUTING INFORMATION PROTOCOL (RIP)
Routing Information Protocol (RIP) is a true distance-vector routing protocol.
It sends the complete routing table out to all active interfaces every 30 seconds
RIP only uses hop count to determine the best way to a remote network
It has a maximum allowable hop count of 15 AD is 120 Bellman-ford algorithm Works well in small networks, but it’s inefficient on large
networks RIP version 1 uses only classful routing, which means that
all devices in the network must use the same subnet mask RIP version 2 does send subnet mask information with the
route updates. This is called classless routing. RIP enable routers can perform EQUAL CAST LOAD
BALANCING by default for 4 paths (max-upto 6 paths)
RIP CONFIGURATION
S0S0
E0E0
192.168.10.1
A B
S0S1
R1# config tR1(config)# )#router ripR1(config)#network 192.168.10.0R1(config)#network 192.168.20.0
R2# config tR2(config)#router ripR2(config)#network 192.168.20.0R2(config)#network 192.168.30.0192.168.10.2
192.168.20.1
192.168.20.2
192.168.30.1
192.168.30.2 192.168.40.1
192.168.40.2
R3# config tR3(config)# )#router ripR3(config)#network 192.168.30.0R3(config)#network 192.168.40.0
DISPLAYING THE IP ROUTING TABLE
DEBUG IP RIP COMMAND
RIP VERSION 2 (RIPV2)
RIP VERSION 2 CONFIGURATION
S0S0
E0E0
192.168.0.16/29
A B
S0S1
192.168.0.4/30 192.168.0.8/30
192.168.0.32/28
Find out the IP Address and SNM of each interfaces
RIP VERSION 2 CONFIGURATION
S0S0
E0E0
192.168.0.18255.255.255.248
A B
S0S1
192.168.0.17255.255.255.248
192.168.0.5255.255.255.252
192.168.0.6255.255.255.252
192.168.0.9255.255.255.252
192.168.0.10255.255.255.252
192.168.0.33255.255.255.240
192.168.0.34255.255.255.240
RIP VERSION 2 CONFIGURATION
S0S0
E0E0
192.168.0.16/29
A B
S0S1
192.168.0.4/30 192.168.0.8/30
192.168.0.32/28R2# config tR2(config)#router ripR2(config)#network 192.168.0.4R2(config)#network 192.168.0.8R2(config)#version 2
R1# config tR1(config)# )#router ripR1(config)#network 192.168.0.4R1(config)#network 192.168.0.16R1(config)#version 2
R3# config tR3(config)# )#router ripR3(config)#network 192.168.0.8R3(config)#network 192.168.0.32R3(config)#version 2