Finding the best way to send and receive messages is one of the most important and complex functions of a router. The most important criteria that routers use for routing are:
- Hop count: The hop counter refers to the number of cross sections in the network. (Hop is part of a route between the origin and destination of a packet.)
- Hypothetical and real bandwidth on a potential path
- Interruption or delay time on a potential route that reduces performance.
- Loading is the traffic or processing that is doing by routers at the time of routing.
- MTU refers to the largest IP packet size assigned to routers. This field allows a packet to be transported to a destination without being broken into and reaching its destination.
- The routing cost is the amount assign to a particular route that is determin by the system administrator. A route that is more desirable and less expensive.
- Potential path reliability, based on statistical data and records.
- Network topology
Routing protocols to determine the best route
Routers communicate with each other through routing protocols to determine the best route. The function of messages sent by routing protocols is similar to that of people searching for unknown lands.
The protocols send messages to gather information about the current state of the network and to help select the best routes and use the data to create routing tables.
Note that routing protocols are not the same as visible protocols such as IP, although routing protocols may be visible on the IP protocol at the destination.
Different routing protocols also operate on different layers of the OSI model, usually Layer 3, Layer 4, or Layer 7.
Routers calculate the priority of data received from routing protocols based on the following criteria:
- Administrative distance, which in common terms means creating a distance for route management and plays an important role in information routing, is one of the important criteria in routing. Each routing protocol has a default managed interval, which is essentially the value that indicates the reliability of the protocol. Lower values indicate more important priorities. This default value can be changed by a network administrator. For example, when a router receives more than one path for a particular subnet, the path that meets the minimum criteria is included in its routing table. When multiple paths of the same criterion are received, it places some of those paths into the routing table based on specific parameters. It also chooses the best route when a router receives route information from several different routing protocols.
- Time Convergence – refers to the time when a group of routers approach convergence. Ideally, routing protocols should have a fast and high time convergence. This approach allows routers to find the best route within the time allowed.
- Slag – A routing protocol based on its own slag or the network infrastructure slag it supports. The slag section of a header contains additional data that is used to send the message.
The most common routing protocols are shown in the table below.
Be aware, however, that there are other routing protocols that have specific functional applications.
RIP (Routing Information Protocol)
|RIPv2 (Routing Information Protocol, version 2)||IGP||
OSPF (Open Shortest Path First)
|IS-IS (Intermediate System to Intermediate System)||IGP||
EIGRP (Enhanced Interior Gateway Routing Protocol)
BGP (Border Gateway Protocol)
Advanced distance-vector or path vector
Quiz Tip : The table above shows a summary of routing protocols. In the NetCorp Plus test, you must have a good understanding of how each routing protocol works and understand how these protocols interact.
Internal and External Gateway Protocols
As you can see in the table above, a routing protocol is classified into one of two IGP or EGP groups. The definition of these two groups is as follows:
- IGPs (Internal Gateway Protocols) are routing protocols used by central routers and edge routers in autonomous systems. IGPs are often divided into the following groups according to the algorithm used to calculate the best paths:
- Distance-distance routing protocols calculate the best route to destination based on distance to destination. Some routing protocols only work on hop-to-destination, while other protocols focus on latency and other network traffic features. Distance-distance routing protocols periodically share their routing information with adjacent routers; routers operating on the basis of such routing protocols must also accept information received from their adjacent routers and cannot independently accept network conditions for Long time and continuous check. RIP, RIPv2, and EIGRP are vector-distance routing protocols.
- State-of-the-art routing protocols enable routers to communicate with routers beyond adjacent routers, so each router can independently determine the network map and the best route between itself and the message destination node. These protocols quickly understand and adapt to network changes, but their configuration is complex and their debugging process is also difficult. OSPF and IS-IS are state-link routing protocols.
- EGP protocols (routing protocols) are routing protocols used by edge routers and external routers to distribute data outside of autonomous systems.
RIP and RIPv2
Routing Information Protocol (RIP) is the oldest routing protocol. When applying the RIP protocol over a network, you need to consider the following considerations:
- Simplicity – Quick and easy setup.
- Stability – This protocol prevents the creation of unlimited routing loops by creating a specific constraint. The maximum metric of this protocol is 15, and if that number is more than 15, the destination will be inaccessible.
- Limited Criteria – Only acceptable when determining the best path between nodes and hop.
- Overloads – Transmits routing tables to other routers every 30 seconds, whether or not the tables have changed.
- Poor Time Convergence – It may take several minutes for new information to be transmit to the network.
- Limited network size – does not work well on very large networks where data can be sent to more than 15 routers.
- Slow down and low security – Newer routing protocols may not support it properly.
Developers of the protocol sought to improve the protocol after its publication in 1988 and introduced the RIPv1 protocol.
(Routing Information Protocol Version 1) named. The latest release, RIPv2 (Routing Information Protocol Version 2), offers less streaming traffic and safer performance than RIPv1.
However, RIPv2 cannot have a maximum metric of more than 15 hop, and therefore remains an outdated routing protocol.
The following figure shows how these protocols work and how they differ.
Select the Shortest Path Protocol (OSPF) Open Shortest Path First is an IGP state-of-the-art routing protocol use in central or edge routers. The above protocol was introduced as a solution to the problems of the RIP protocol. A protocol capable of interacting with RIP or RIPv2 protocols on the network. Features of this protocol include:
- Supports large networks – does not have hub restrictions on a transit path.
- Complex algorithms – Calculate and find the best and most efficient transition path compared to the RIP protocol. In ideal network conditions, it finds the best and most direct route between two points. If the level of network traffic is too high and data is not available directly, then a router may use additional routers to select the most efficient route. In fact, it is the OSPF protocol that assists the router in this regard.
- Shared data – a database of links from other routers. If the OSPF detects that a given link is broken, the router can quickly calculate and replace another proposed path.
- Low slip and fast convergence – This protocol requires more memory to perform computations and consumes slightly more CPU power than normal, but preserves network bandwidth as much as possible with very fast convergence times that are not felt by most users. he does.
- Stability – Uses algorithms that prevent routing loops.
- Supporting by other routers – This protocol is supporting by most modern routers. The above protocol is mainly used in autonomous systems that may use a combination of routers manufactured by different manufacturers.
Intermediate System to Intermediate System (IS-IS) is an IGP and state-of-the-art routing protocol. IS-IS uses a better algorithm than OSPF, which is essentially a standard.
ISO, but the IETF eventually adopt this protocol as an Internet standard, however, unlike OSPF, IS-IS was design for use in central routers. The IS-IS protocol is much like IPv4, much like the OSPF protocol.
As a result, it is fully compatible with IPv6. Service providers usually prefer to use IS-IS on their networks because of the scalability. It’s better than OSPF, but OSPF is still more common.
Enhanced Interior Gateway Routing Protocol (EIGRP) is an IGP protocol developed by Cisco Systems in the mid-80s.
The above protocol is an advanced vector-distance protocol that uses some of the features of the state-of-the-art protocol and is sometimes referred to as a hybrid protocol. With fast convergence and low network overhead, it is easier to configure and reduce CPU usage than OSPF.
EIGRP also offers the benefits of supporting multiple protocols and limiting unnecessary network traffic between routers.
Initially, EIGRP was included in Cisco routers, but in 2013 parts of the EIGRP standard were publicly released to allow networks using different routers to use EIGRP.
This approach creates very large and heterogeneous networks, yet it is still optimize for Cisco routers and many manufacturers are still unable to properly support it.
In local networks that use Cisco routers exclusively, EIGRP is generally preferred over OSPF.
(BGP (Border Gateway Protocol
The only external gateway protocol (EGP) is the Border Gateway Protocol (BGP), which enables communication between independent systems, also known as the Internet Protocol.
While both OSPF and IS-IS protocols limit the number of routers in a given area, the BGP protocol does not have this limitation because of the need to not directly connect two routers to one network.
BGP consists of several standalone systems and is used by edge and outer routers on the Internet.
The BGP Index features include:
- Routing-vector routing protocols in a communication network can be exchanged via specific BGP messages that are routed between routers during TCP sessions.
- Efficient – Determines the best routes based on many different factors.
- Adjustable – The above protocol can be configure to work according to specific policies. For example, avoiding the use of a particular router or commanding a group of routers to select a particular route when other routes are available.
- BGP is the most sophisticated routing protocol we mentioned in this article.
Quiz Tip :
BGP considers many factors to determine the best paths and is more complex than distance-vector protocols. In fact, it is this compatibility capability that has made the above-mentioned protocol popular because of its high scalability.
You may also see BGP as an advanced routing-vector routing protocol, as it holds dynamic route information beyond adjacent routers.
However, due to the complexity and multiplicity of factors that can be considered when calculating the best paths, the NetCorps test defines the BGP protocol as a hybrid routing protocol,
since it incorporates both the features of distance-vector and state-of-the-band routing protocols. Can be.