Understand routing tables and routing protocols

Routing is the process of sending data from one host on a network to another via a router. In order for the router to know how to forward packets to the destination address using the best path, the router needs a routing map or table in which there is a routing protocol to determine which path the packet will take.

Read also: Understanding static and dynamic routing

routing table

A routing table (routing table) is a table that contains information about the presence of networks, both directly connected networks (directly connected networks) and not directly connected networks (remote networks). This table also contains information about how the router accesses the network. This routing table is very important because the router is used as a guide to send every data packet it receives. The information in the routing table is in the form of network address lines called entry paths.

Also in each entry is a path of information about the interface that the router can use to send data packets. If the router receives a data packet, the router will check the destination IP address (destination address) of the packet, then match it with the network address in each entry in the routing table, and if there is a match, the router will forward the packet to the interface when it is used to send the packet. The interface used to forward packets is called the outgoing interface or the outgoing interface, but if there is no matching input, the router will discard the packet. There are 4 classes of entries in the routing table.

routing table input

  • Directly connected network: This entry will appear when the router interface is activated and an IP address is configured, and the directly connected entry will have a label C.
  • fixed ways: This entry is an entry that is manually filled in by the network administrator, so if there is a change in the network, this entry must also be changed manually, Static Route Enry will have an S label.
  • dynamic modes: This entry is an entry that will appear due to the results of routing information exchange from multiple routers, routing information exchange will use the routing protocol. This entry is not manually filled in by the network administrator, the network administrator only needs to activate the routing protocol and the network on this router, the dynamic path of entry will have the label D3.
  • default methods: This entry is used to specify where the packet will be sent to if the packet’s destination address is not in the routing table, and this default input path can be configured manually (static) or obtained from information exchange from the routing protocol (dynamic). The default path entry is an entry with parameter value DstAddress = / 0, if configured statically, the default path will have a label S.

There is also some information in the routing table.

Routing table information

  • Dst.Address: The information in this column indicates the destination network (destination) that the router can reach.
  • Pref-Src: The information in this column will show the IP address used by the router as the sender’s IP address field.
  • Gateway: This column will show how the router is accessing the network in the Dst.Address column, usually in the form of an interface or an IP address from a neighboring router that can be used to access the remote network.
  • Distance: This column shows the Administrative Distance (AD) value. The AD value can indicate whether the input is obtained by a router from a static or dynamic router, and it can also be used to find out what type of protocol is being used. It can also be used to find out if the input is a directly connected network.

routing protocol

Routing protocol (Routing protocol) is the way routers make decisions to determine where to send packets. The routing protocol will be used by routers that use dynamic routing. The routing protocol will exchange routing tables with other routers that use dynamic routing. So if there is a change in the network, this protocol will automatically notify all the routers on the network. There are several types of routing protocols.

Types of routing protocol types

RIP (Routing Information Protocol)

RIP stands for Routing Information Protocol. This protocol provides routing table updates based on the connected router directly, then the next router will provide information about the next router connected to the router. The information exchanged by RIP is host, network, subnet, default path. Routing updates are performed every 30 seconds. This protocol is usually used in LAN and WAN networks because this protocol is classified as an internal gateway protocol. So far, RIP has been adapted for use on IPv6 networks known as the RIPng standard.

IGRP (Internal Gateway Routing Protocol)

IGRP stands for Inferior Gateway Protocol. This protocol was developed in the mid-1980s Cisco Systems, Inc. With the main objective to provide a robust protocol for routing in AS (autonomous systems). IGRP performs distance-based routing mathematically. Therefore, IGRP considers bandwidth, delay, load, and reliability before deciding which path to take for the data stream.

OSPF (Open Short Path First)

OSPF stands for Open Short Path First. This protocol is an open standard protocol that may have been implemented by a number of network vendors. OSPF works using an algorithm known as Dijkstra algorithm. First, the shortest path tree will be created, then the routing table will be populated with the best paths generated from the tree. OSPF only works on IP routing.

IS-IS (Intermediate System – Intermediate System)

IS-IS is a link state routing protocol belonging to the IGP (Internal Gateway Protocol) class. IS-IS uses Dijkstra algorithms such as OSPF to determine routing paths. In IS-IS, there is also the concept of a region such as OSPF, but the region in IS-IS is different from the region in OSPF. If in OSPF the regions are separated by different interface regions, then in IS-IS, the regions are separated by links that connect routers in one region with routers in other regions. In other words, a router will only have one zone, but one zone can contain multiple routers.

EIGRP (Enhanced Down Gate Protocol)

EIGRP or Enhanced Down Gateway Protocol is a development of IGRP. EIGRP still performs routing based on mathematically calculated distances. This protocol is only available on Cisco routers. EIGRP is used on routers to share paths with other routers on the same autonomous system. EIGRP only sends additional updates, which reduces the workload of the router and the amount of data that must be sent.

BGP (Border Gateway Protocol)

BGP or Border Gateway Protocol is the backbone of the World Wide Web as it is the core of the Internet Routing Protocol. BGP works by setting an Internet protocol table that indicates which network can be accessed between independent systems. BGP does not use traditional IGP metrics, but makes routing decisions based on routes, network policies, and rule sets. Currently, version 4 of BGP is still in use.

class in routing protocol

distance vector: This is a class class protocol that will determine the best network path based on the distance traveled by the path. Route paths with short distance to the destination network will be the best route choice.

link status: Also known as the shortest path first protocol. The function of the routing table on a router that implements this type of protocol is quite unique, because the function of the routing table is divided into three separate tables. One is to record changes in directly connected networks, the other is to define the structure of the entire internetwork, and one last table is used as the routing table.

hybridExamples of protocols that fall into this category use aspects of distance vector routing protocols and link state routing protocols.


routing protocol It is a base for exchanging information routing which will later form a file routing table So that the address of the data packets to be sent becomes clearer and routing protocol It will be able to find the shortest way to send data packets to the destination address.

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