4. Indirect Delivery
To send a packet from source to destination
packet should go from router to router
All routers should maintain a routing table
IP packet is analyzed at the router and correct path is
selected form the routing table
The packet is sent though that path
Indirect delivery is done using the routing strategies
5. Routing Strategies
There are four routing strategies
- Fixed Routing
- Flooding
- Random Routing
- Adaptive Routing
6. Fixed Routing
Routing information is centrally maintained
This is called a Directory (A central database)
Advantage
- Updating new information is easy as need to change at one
location (central Database)
Disadvantages
- Each and every IP packet should be analyzed
- Network traffic may increase at the central database because it
has to serve lots of requests from routers
- Dynamic changes are not possible
7. Flooding
When an IP packet comes, the router will send it on all paths.
- retransmitted to neighbors
Advantages
- Simple mechanism (IP packets are not analyzed at router)
- Most likely it will reach the destination (Highly reliable)
Disadvantages
- Causes high network traffic
- Duplicate packets might reach the destination
- Wastes Network bandwidth
8. Random Routing
When an IP packet comes to the router, it decides the
path randomly and sends the IP packet in that path
Advantages
- Will not cause unnecessary network traffic
- Simple
Disadvantage
- No guarantee that the IP packet will reach to the
destination
9. Adaptive Routing
Each router maintains a routing table
Also it can be changed according to the network changes
(Adaptive)
Advantages
- Network traffic is minimized
- The best route will be selected most of the time
Disadvantages
- Routers need to keep a routing table
- Process each IP packet
- Need to update routing tables automatically with the changes
in the network
10. Routing Methods used in Adaptive
Routing
Next hop routing
Host specific
Network specific
Default routing
11. Host Specific Routing
Each router keeps a table entry for each host (one record for
one host)
Table entry has Host IP and the Interface
Host Address Interface
A E0
B S0
C S1
Disadvantages
• Large number of records (if multiple paths are available number
of records increases)
•Table updating is difficult and complex as it should be done for
each and every host (if the host IP changes)
12. Network Specific Routing
Each router keeps a table entry for each network (one record
for one network)
Table entry has Network address and Interface
Advantages
• Number of records are limited (Table updates are not for each
host but for a network)
•Update is easy
Network Address Interface
A E0
B S0
C S1
13. Default Routing
Another record in the routing table
Indicates the route/path to be taken, if any of the records does not
match with the IP packet destination IP address
Stub networks only use default routing , which means that they
have only one exit port out of the network
14. Routing Table update Methods
Basically there are three methods to update routing
tables
- Connected
- Static
- Dynamic
15. Connected
Once the router is connected to the network its interfaces
are given IP addresses
With that router automatically identifies the network
addresses to which it connected
17. Dynamic
Routing tables are updated automatically by using
routing rules ( protocols )
Routing tables have
Initially only ‘connected’ records
Then add few ‘static’ records
Then add dynamic updates
19. Features of routing protocols
Network changes (addition or removal or fault) are
automatically updated in routing tables of all routers
When there are many routes to a destination, the
best route should be selected
Share the traffic through different routes
20. What Is a Routing Protocol?
Routing Protocols
allow routers to
dynamically
advertise and
learn routes,
determine which
routes are
available and
which are the
most efficient
routes to a
destination
20
Network
Protocol
Destination
Network
Connected
RIP
IGRP
10.120.2.0
172.16.2.0
172.17.3.0
Exit
Interface
E0
S0
S1
Routing Protocol: RIP, IGRP,OSPF
172.17.3.0
172.16.1.010.120.2.0
E0
S0
22. Routing Protocols cont.
An autonomous system (AS) is a collection of routers
under a common administration
ex : a company's internal network
Interior Gateway Protocols (IGP) are used for
intra-autonomous system routing
(routing inside an autonomous system)
Exterior Gateway Protocols (EGP) are used for
inter-autonomous system routing
(routing between autonomous systems)
24. Distance Vector Routing Protocols
Routes are advertised as vectors of distance and direction
Distance is defined in terms of a metric such as hop count and
direction is simply the next-hop router or exit interface
Send periodic updates of their routing information
Use the Bellman-Ford algorithm for best path selection
Work best in situations where:
- Network is simple
- Administrators do not have enough knowledge to configure
Ex : RIP, IGRP, EIGRP
25. Link State Routing Protocols
link-state routing protocol send information about the state of
its links to other routers in the routing domain
The state of those links includes information about the type of
network and any neighboring routers on those networks
A link-state update only sent when there is a change in the
topology
Use the Dijkstra algorithm for best path/ route selection
Work best in situations where:
- Network design is complex (large networks)
- Administrators have a good knowledge of network
Ex : OSPF, IS-IS