1. Dalya A.Alrahim Aljubori
Routing Protocols
Dalya A.Alrahim Aljubori

2. Table of content 1-Routing Table 2- Types of routing: -Static routing
-Dynamic routing
3-Routing protocol
4-Dynamic Routing Protocols types
5-Classifying Routing Protocols
6-Distance Vector Routing Protocols
7-Routing Protocol Metrics
8-Routing Information Protocol (RIP)
9-Differences between RIPv1 or RIPv2
10-Routing Protocol Characteristics
11-Administrative Distance
12-Selecting the Best Route
13-Route Summarization

3. Routing Table
Routing is the process your computer uses to transmit a packet between different subnets. If you want to communicate with a computer on a different subnet from your own, your computer must forward the data packets to a router. A router is the software and hardware responsible for delivering packets between two subnets. Each router uses an internal routing table to determine the best path to send a packet.

4. A routing table is a set of rules, often viewed in table format, that is used to determine where data packets traveling over an Internet Protocol (IP) network will be directed. All IP-enabled devices, including routers and switches, use routing tables.
A routing table contains the information necessary to forward a packet along the best path toward its destination. Each packet contains information about its origin and destination. When a packet is received, a network device examines the packet and matches it to the routing table entry providing the best match for its destination. The table then provides the device with instructions for sending the packet to the next hop on its route across the network.

5. A basic routing table includes the following information:
Destination: The IP address of the packet's final destination
Next hop: The IP address to which the packet is forwarded
Interface: The outgoing network interface the device should use when forwarding
the packet to the next hop or final destination
Metric: Assigns a cost to each available route so that the most cost-effective path
can be chosen
Routes: Includes directly-attached subnets, indirect subnets that are not attached to
the device but can be accessed through one or more hops, and default routes to use
for certain types of traffic or when information is lacking.

6. Viewing the Routing Tables
If you want to see the routing tables, you will have to open a Command Prompt window and then enter the ROUTE PRINT command. Upon doing so, you will see a screen similar to the one that’s shown in Figure A.

7. Two main types of routing: 1-Static routing 2-Dynamic routing
Routing tables can be maintained manually or dynamically. Tables for static network devices do not change unless a network administrator manually changes them. In dynamic routing, devices build and maintain their routing tables automatically by using routing protocols to exchange information about the surrounding network topology. Dynamic routing tables allow devices to "listen" to the network and respond to occurrences like device failures and network congestion.

8. Static Routing
The term static routing denotes the use of manually configured or injected static routes for traffic forwarding purposes. Using a static route might be appropriate in the following circumstances:
1- When it is undesirable to have dynamic routing updates forwarded across slow bandwidth links, such as a dialup link
2-When the administrator needs total control over the routes used by the router
3-When a backup to a dynamically learned route is necessary
4-When it is necessary to reach a network that is accessible by only one path (a stub network)
Configuring and maintaining static routes is time-consuming. Properly implementing static routes requires complete knowledge of the entire network.

9. Dynamic Routing
Dynamic routing allows the network to adjust to changes in the topology automatically, without administrator involvement. A static route cannot dynamically respond to changes in the network.
If a link fails, the static route is no longer valid if it is configured to use that failed link, so a new static route must be configured. If a new router or new link is added, that information must also be
configured on every router in the network. In a very large or unstable network, these changes can lead to considerable work for network administrators. It can also take a long time for every router
in the network to receive the correct information. In situations such as these, it might be better to have the routers receive information about networks and links from each other using a dynamic
routing protocol. Dynamic routing protocols must do the following:

10. Find sources from which routing information can be received (usually neighboring routers)
Select the best paths toward all reachable destinations, based on received information
Maintain this routing information
Have a means of verifying routing information (periodic updates or refreshes)
When using a dynamic routing protocol, the administrator configures the routing protocol on each router. The routers then exchange information about the reachable networks and the state of each
network. Routers exchange information only with other routers running the same routing protocol. When the network topology changes, the new information is dynamically propagated throughout the network, and each router updates its routing table to reflect the changes.

11. Routing protocol
A routing protocol specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network. Routing algorithms determine the specific choice of route. Each router has a priori knowledge only of networks attached to it directly. A routing protocol shares this information first among immediate neighbors, and then throughout the network. This way, routers gain knowledge of the topology of the network.

12. The router learns about remote networks from neighbor routers or from an administrator. The router then builds a routing table. If the network is directly connected then the router already knows how to get to the network. If the networks are not attached, the router must learn how to get to the remote network with either static routing (administrator manually enters the routes in the router's table) or dynamic routing (happens automatically using routing protocols like EIGRP,OSPF,etc.).
The routers then update each other about all the networks they know. If a change occurs a router goes down, the dynamic routing protocols automatically inform all routers about the change. If static routing is used, then the administrator has to update all changes into all routers and therefore no routing protocol is used.

13. Only Dynamic routing uses routing protocols, which enable routers to:
Dynamically discover and maintain routes
Calculate routes
Distribute routing updates to other routers
Reach agreement with other routers about the network topology

14. Dynamic Routing Protocols types
There are 3 types of Dynamic routing protocols, these are differ by the way that discover and make calculations about routes;
1. Distance Vector
2. Link State
3. Hybrid
Distance Vector routers find the best path from information send from neighbors
Link State routers each have a copy of the entire network map
Link State routers find best routes from this local map

15. The Table below shows the main characteristics of a few different types of dynamic routing protocols:

16. You can also classify the routing protocols in terms of their location on a network. For example, routing protocols can exist in, or between, autonomous systems.

17. Classifying Routing Protocols
Routing protocols can be classified into different groups according to their characteristics. Specifically, routing protocols can be classified by their:
Purpose: Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP)
Operation: Distance vector protocol, link-state protocol, or path-vector protocol
Behavior: Classful (legacy) or classless protocol
For example, IPv4 routing protocols are classified as follows:
RIPv1 (legacy): IGP, distance vector, classful protocol
IGRP (legacy): IGP, distance vector, classful protocol developed by Cisco (deprecated from 12.2 IOS and later)
RIPv2: IGP, distance vector, classless protocol
EIGRP: IGP, distance vector, classless protocol developed by Cisco
OSPF: IGP, link-state, classless protocol
IS-IS: IGP, link-state, classless protocol
BGP: EGP, path-vector, classless protocol

18. The classful routing protocols, RIPv1 and IGRP, are legacy protocols and are only used in older networks. These routing protocols have evolved into the classless routing protocols, RIPv2 and EIGRP, respectively. Link-state routing protocols are classless by nature.

19. A hierarchical view of dynamic routing protocol classification:

20. Distance Vector Routing Protocols
Distance vector means that routes are advertised by providing two characteristics:
Distance: Identifies how far it is to the destination network and is based on a metric such as the hop count, cost, bandwidth, delay, and more
Vector: Specifies the direction of the next-hop router or exit interface to reach the destination
A router using a distance vector routing protocol does not have the knowledge of the entire path to a destination network. Distance vector protocols use routers as sign posts along the path to the final destination. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there. Distance vector routing protocols do not have an actual map of the network topology.

21. In a distance vector protocol, routing decisions are made on a hopby-hop basis. Each router relies on its neighbor routers to make the correct routing decisions.The router passes only the results of this decision (its routing table) to its neighbors. Distance vector protocols are typically slower to converge and do not scale well; however, they are easy to implement and maintain. Examples of distance vector protocols include RIPv1, RIPv2, and Interior Gateway Routing Protocol (IGRP).

22. For example, in the figure , R1 knows that the distance to reach network /24 is one hop and that the direction is out of the interface Serial 0/0/0 toward R2.

23. There are four distance vector IPv4 IGPs:
RIPv1: First generation legacy protocol
RIPv2: Simple distance vector routing protocol
IGRP: First generation Cisco proprietary protocol (obsolete and replaced by EIGRP)
EIGRP: Advanced version of distance vector routing

24. Routing Protocol Metrics
There are cases when a routing protocol learns of more than one route to the same destination. To select the best path, the routing protocol must be able to evaluate and differentiate between the available paths. This is accomplished through the use of routing metrics.
A metric is a measurable value that is assigned by the routing protocol to different routes based on the usefulness of that route. In situations where there are multiple paths to the same remote network, the routing metrics are used to determine the overall “cost” of a path from source to destination. Routing protocols determine the best path based on the route with the lowest cost.
Different routing protocols use different metrics. The metric used by one routing protocol is not comparable to the metric used by another routing protocol. Two different routing protocols might choose different paths to the same destination.

25. If a routing protocol recognizes more than one way to reach a network, it compares the metric for each different path and chooses the path with the lowest metric. If multiple paths have the same metric, a maximum of 16 can be installed in the routing table (the maximum number of parallel routes), and the router can perform load balancing among them.

26. For example, assume that PC1 wants to send a packet to PC2
For example, assume that PC1 wants to send a packet to PC2. In the Figure, the RIP routing protocol has been enabled on all routers and the network has converged. RIP makes a routing protocol decision based on the least number of hops. Therefore, when the packet arrives on R1, the best route to reach the PC2 network would be to send it directly to R2 even though the link is much slower that all other links.

27. In the Figure, the OSPF routing protocol has been enabled on all routers and the network has converged. OSPF makes a routing protocol decision based on the best bandwidth. Therefore, when the packet arrives on R1, the best route to reach the PC2 network would be to send it to R3, which would then forward it to R2.

28. Routing Information Protocol (RIP)
Is a standards-based, distance-vector, interior gateway protocol (IGP) used by routers to exchange routing information. RIP uses hop count to determine the best path between two locations. Hop count is the number of routers the packet must go through till it reaches the destination network. The maximum allowable number of hops a packet can traverse in an IP network implementing RIP is 15 hops.
it has a maximum allowable hop count of 15 by default, meaning that 16 is deemed unreachable. RIP works well in small networks, but it's inefficient on large networks with slow WAN links or on networks with a large number of routers installed.
In a RIP network, each router broadcasts its entire RIP table to its neighboring routers every 30 seconds. When a router receives a neighbor's RIP table, it uses the information provided to update its own routing table and then sends the updated table to its neighbors.

29. RIP
is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination. The maximum number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. A hop count of 16 is considered an infinite distance and the route is considered unreachable.
In most networking environments, RIP is not the preferred choice for routing as its time to converge and scalability are poor compared to EIGRP, OSPF, or IS-IS. However, it is easy to configure, because RIP does not require any parameters unlike other protocols.
RIP uses the User Datagram Protocol (UDP) as its transport protocol, and is assigned the reserved port number 520.

30. Versions
There are three versions of the Routing Information Protocol: RIPv1, RIPv2, and RIPng.
RIP version 1
The original specification of RIP, defined in RFC 1058, was published in 1988 and uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.

31. RIP version 2
Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993,and last standardized in It included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). To maintain backward compatibility, the hop count limit of 15 remained.
(MD5) authentication for RIP was introduced in 1997.
MD5 stands for Message Digest algorithm 5
Route tags were also added in RIP version 2. This functionality allows a distinction between routes learned from the RIP protocol and routes learned from other protocols.

32. RIPng
RIPng (RIP next generation), defined in RFC 2080,is an extension of RIPv2 for support of IPv6, the next generation Internet Protocol.
The main differences between RIPv2 and RIPng are:
Support of IPv6 networking.
While RIPv2 supports RIPv1 updates authentication, RIPng does not. IPv6 routers were, at the time, supposed to use IPsec for authentication.
Internet Protocol Security (IPsec) is a protocol suite for secure Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session.
RIPv2 encodes the next-hop into each route entry, RIPng requires specific encoding of the next hop for a set of route entries.
RIPng sends updates on UDP port 521 using the multicast group FF02::9.

33. Differences between RIPv1 or RIPv2
This is a simple distance vector protocol. It has been enhanced with various techniques, including Split Horizon and Poison Reverse in order to enable it to perform better in somewhat complicated networks.
A classful protocol, broadcasts updates every 30 seconds, hold-down period 180 seconds. Hop count is metric (Maximum 15).

34. This version added several new features.
RIPv2
This version added several new features.
RIPv2 uses multicasts, version 1 use broadcasts,
RIPv2 supports triggered updates—when a change occurs, a RIPv2 router will immediately propagate its routing information to its connected neighbors.
RIPv2 is a classless protocol. RIPv2 supports variable-length subnet masking (VLSM)
RIPv2 supports authentication. You can restrict what routers you want to participate in RIPv2. This is accomplished using a hashed password value.

35. RIP uses four different kinds of timers to regulate its performance:
Route update timer
Sets the interval (typically 30 seconds) between periodic routing updates in which the router sends a complete copy of its routing table out to all neighbors.
Route invalid timer
Determines the length of time that must elapse (180 seconds) before a router determines that a route has become invalid. It will come to this conclusion if it hasn’t heard any updates about a particular route for that period. When that happens, the router will send out updates to all its neighbors letting them know that the route is invalid.

36. Holddown timer
This sets the amount of time during which routing information is suppressed. Routes will enter into the holddown state when an update packet is received that indicated the route is unreachable. This continues either until an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds.
The hold-down timer is started per route entry, when the hop count is changing from lower value to higher value. This allows the route to get stabilized. During this time no update can be done to that routing entry.
Route flush timer
The flush timer controls the time between the route is invalidated or marked as unreachable and removal of entry from the routing table. By default the value is 240 seconds. This is 60 seconds longer than Invalid timer. So for 60 seconds the router will be advertising about this unreachable route to all its neighbours. This timer must be set to a higher value than the invalid timer.

37. Routing Protocol Characteristics
Routing protocols can be compared based on the following characteristics:
Speed of convergence: Speed of convergence defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence, the more preferable the protocol. Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network.
Scalability: Scalability defines how large a network can become, based on the routing protocol that is deployed. The larger the network is, the more scalable the routing protocol needs to be.
Classful or classless (use of VLSM): Classful routing protocols do not include the subnet mask and cannot support variable-length subnet mask (VLSM). Classless routing protocols include the subnet mask in the updates. Classless routing protocols support VLSM and better route summarization.

38. Resource usage: Resource usage includes the requirements of a routing protocol such as memory space (RAM), CPU utilization, and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing protocol operation, in addition to the packet forwarding processes.
Implementation and maintenance: Implementation and maintenance describes the level of knowledge that is required for a network administrator to implement and maintain the network based on the routing protocol deployed.
Routing protocols vary in their support for many features, including VLSM, summarization, scalability, and fast convergence. There is no best protocol—the choice depends on many factors.

39. Comparing Routing Protocols

40. Administrative Distance
Most routing protocols have metric structures and algorithms that are incompatible with other protocols. It is critical that a network using multiple routing protocols be able to seamlessly
exchange route information and be able to select the best path across multiple protocols. Cisco routers use a value called administrative distance to select the best path when they learn of two or more routes to the same destination from different routing protocols.
Administrative distance rates a routing protocol’s believability. Cisco has assigned a default administrative distance value to each routing protocol supported on its routers. Each routing protocol is prioritized in order, from most to least believable.
Administrative distance is a value between 0 and 255. The lower the administrative distance value, the higher the protocol’s believability.

41. Administrative Distance of Routing Protocols

43. Selecting the Best Route
Cisco routers use the following two parameters to select the best path when they learn two or more routes to the same destination from different routing protocols:
1- Administrative distance: The administrative distance is used to rate a routing protocol’s believability. This criterion is the first thing a router uses to determine which routing protocol to believe if more than one protocol provides route information for the same destination.
2- Routing metric: The routing metric is a value representing the path between the local router and the destination network, according to the routing protocol being used. This metric is used to determine the routing protocol’s “best” path to the destination.

44. Route Summarization
Route summarization (which is also called route aggregation or supernetting). In route summarization, a single summary address in the routing table represents a set of routes.Summarization reduces the routing update traffic, the number of routes in the routing table, and the overall router overhead in the router receiving the routes.

45. The Benefits of Route Summarization
A large flat network is not scalable because routing traffic consumes considerable network resources. When a network change occurs, it is propagated throughout the network, which requires processing time for route recomputation and bandwidth to propagate routing updates.
A network hierarchy can reduce both routing traffic and unnecessary route recomputation. To accomplish this, the network must be divided into areas that enable route summarization. With summarization in place, a route flap (a route that goes down and up continuously) that occurs in one network area does not influence routing in other areas. Instabilities are isolated and convergence is improved, thereby reducing the amount of routing traffic, the size of the routing tables, and the required memory and processing power for routing. Summarization is configured manually, or occurs automatically at the major network boundary in some routing protocols.