Routing is used for the process of taking a packet from a device and sending it through a network to another device on a different network. If your network does not have a router, then obviously you are not doing routing.
To be able to do packet routing, there are things to know:
• Destination address
• The neighboring routers from which a router can learn about remote networks
• Possible routes to all remote networks
• The best route for any remote network
The router stores a routing table that describes how to find remote networks.
The types of routing are:
• Static routing
• Default routing
• Dynamic routing
IP Routing Process
The IP routing process can be explained,
The default gateway of host 172.16.10.2 (Host_A) is configured to 172.16.10.1. To be able to send this packet to the default gateway must be known hardware address of the Ethernet interface 0 on the router (configured with the IP address 172.16.10.1). Why is that? For packets to be submitted to the Data Link layer , then encapsulated into frames , and sent to the router interface connected to network 172.16.10.0. Hosts communicate only with hardware addresses on local LAN. It is important to understand that Host_A, in order to communicate with Host_B, must send the packet to the MAC address of the default gateway on the local network.
Static routing occurs when the Admin manually adds routers in the routing table of each router.
Static routing has the following advantages:
- No overhead (processing time) on the router CPU (router is cheaper than dynamic routing)
- No bandwidth is used between routers.
- Static routing adds security, as Administrators can choose to load access routing to certain networks only.
Static routing has the following losses:
- The administration should really understand the internetwork and how each router is connected to be able to properly configure the router.
- If a network is added to the internetwork, the Administration must add a route to all routers-manually.
- Static routing is not appropriate for large networks because it will be a full-time job on its own.
The default routing is used to send packets manually adding the router to a remote destination network that is not in the routing table, to the next hop router. Usually used on networks that have only one exit point.
Dynamic routing is when routing protocols are used to find the network and update routing tables on the router. And this is easier than using static and default routing, but it will differentiate you in terms of processes in the router CPU and bandwidth usage of network links
Routed and Routing Protocol
Protocol is nothing but a formal description of a set or rule-rule and conversion that determines how devices in a network exchange information. Here are two basic types of protocols.
Are protocols that can be routed by a router. Routed protocols allow routers to precisely interpret logical networks. Examples of routed protocols: IP, IPX, AppleTalk, and DECnet.
These protocols are used to maintain routing tables on routers. Examples of routing protocols include OSPF, RIP, BGP, IGRP, and EIGRP
Routing Information Protocol. Distance vector protocol – maintains a list of mileage to other networks based on the number of hops, ie the number of routers that the packets must pass through to reach the destination address. RIP is limited to 15 hops. The broadcast is updated in every 30 seconds for all RIP routers to maintain integrity. RIP is suitable for small networks.
Open Shortest Path First. Link state protocol – uses network speeds based on metrics to assign paths to other networks. Each router maintains a simple map of the entire network. Updates are done via multicast and sent. If a configuration change occurs. OSPF is suitable for large networks.
Enhanced Interior Gateway Routing Protocol. Distance vector protocol maintains a complex set of metrics for mileage to other networks. EIGRP also incorporates the concept of link state protocol. Broadcasts are updated every 90 seconds to all adjacent EIGRP routers. Each update only includes network changes. EIGRP is perfect for large networks.
It is a distance vector exterior gateway protocol that works intelligently to maintain paths to other networks. Up date are sent over a TCP connection.
The administrative distance (AD) is used to measure what is called trustworthiness of routing information received by a router from neighboring routers. AD is an integer number 0 – 255, where 0 is the most reliable and 255 means no data traffic will pass through this route.
If both routers receive two updates about the same remote network, then the first thing checked by the router is AD. If one of the advertised routes (announced by another router) has an AD lower than the other, then the route with the lowest AD will be placed in the table.
If the two advertised routes have the same AD, then the so-called metric of the routing protocol (such as the number of hops or bandwidth of the connection) will be used to find the best path to the remote network. If still the same both AD and metric, then used load-balance (load balancing).
|Source route||AD Default|
|Directly connected interface||0|
|Not known||255 (never used|
There are three classes of routing protocols
Distance vector Distance-vector protocol finds the best path to a remote network by assessing distance. Routes with the least hop distance to the destination network would be the best route. Both RIP and IGRP are distance-vector routing protocols. RIP and IGRP send all routing tables to connected routers directly.
Link state Or also called the shortest-path-first protocol, each router will create three separate tables. One of these tables will record changes from the connected networks directly, another table determines the topology of the entire internetwork, and the last table is used as the routing table. OSPF is a fully link-state IP routing protocol. Link-state protocols send updates containing the status of their own links to all other routers on the network.
Hybrid The hybrid protocol uses aspects of the distance vector type routing protocol and the link state type routing protocol – for example EIGRP.
Routing Protocol Type Distance-Vector
The distance-vector routing algorithm sends the contents of the complete table routing to neighboring router routers, which then combines the entries in the routing of the received tables with their routing tables, to complete the routing table of the router.
Routing Information Protocol (RIP) sends a complete routing table to all active interfaces every 30 seconds. RIP only uses hop count to determine the best way to a remote network, but RIP by default has a value of the maximum allowable number of hops, which is 15, mean value 16 unreachable ( unreachable ). RIP works well on small networks, but RIP is not efficient on large networks with WAN links or networks that use multiple routers.
RIP v1 uses classful routing, which means all the tools on the network must use the same subnet mask. This is because RIP v1 does not send updates with subnet mask information in it. RIP v2 provides something called prefix routing and can send subnet mask information along with updates from the route. This is called classless routing
Interior Gateway Routing Protocol (IGRP) is a Cisco-proprietary ( cisco-proprietary ) distance-vector routing protocol. This means that all your routers must be a Cisco router to use IGRP on your network.
IGRP has a maximum number of hops of 255, with a default value of 100. This helps the shortcomings of RIP.
Enhance Interior Gateway Routing Protocol (EIGRP) is a routing protocol
The enhanced Cisco ( cisco-proprietary ) distance-vector, which gives an edge over IGRP. Both use the concept of an autonomous system to describe a collection of contiguous routers that run the same routing protocol and share routing information. But EIGRP inserts a subnet mask into its update route. Thus allowing us to use VLSM and do Summary ( summarization ). EIGRP has a maximum number of hops 255. Here are EIGRP features that are much better than IGRP
- Supports IP, IPX, and AppleTalk through protocol-dependent modules
- Search for a neighbor network efficiently
- Communication through Reliable Transport Protocol (RTP)
- Selection of best path through Diffusing Update Algorithm (DUAL)
Routing Protocol Type link-state
Open Shortest Path First (OSPF) is an open standard protocol that has been implemented by a number of network vendors. If you have many routers, and not all of them are Cisco, then you can not use EIGRP, so your choice is RIP v1, RIP v2, or OSPF. If it is a large network, then your only choice is only OSPF or something called route redistribution – a translation service between routing protocols.
OSPF works with an algorithm called the Dijkstra algorithm. First, the shortest path tree will be built, and then the routing table will be populated with the best paths generated from the tree. OSPF only supports IP routing only.