What is Router

Why should the router

Before we learn more about how to configure cisco router, we need to understand better some of the basic rules of the routing. Also we would have to understand the numbering system IP, subnetting, netmasking and more.

Example case:
Host X à (Class B IP network 128.1.xx id)
Host Y à (class B IP network 128.1.xx id)
Host Z à (class B IP network 128.2.xx id)

In the above case, the host X and host Y can communicate directly but good X or Y host is unable to communicate with host Z, because they have different network id. How so Z can communicate with the X and Y? use a router.

Example use cases subnetting

  • Host P à subnet mask
  • Host Q à subnet mask
  • Host R à subnet mask

Well, when subnetting is invoked, then the two hosts connected to the same network segment can communicate only if good network appropriate subnet id. In cases above, P and Q can communicate directly, R has the same network id with P and Q, but have different subneting. Thus R can not communicate directly with P and Q. How so R can communicate with P and Q? use the router!

So the function of the router, is easy to say, connecting two different networks, precisely directing the best route to achieve the desired network.

In implementation, the router often used to connect network among agencies or enterprises respectively have networks with different network id. Other examples that are currently popular is when enterprise will connect to the Internet. Then the router will work flowing from your enterprise data packets to other institutions via the internet, of course it will calm your network ID with your company direction.

If simply connect 2 networks, you actually can use windows based on PC NT or Linux. To give 2 network cards and a little settings, you actually have to make practical router. But of course with all its limitations.

In a highly diversified market brand router, among others baynetworks, 3com and cisco. This module of the course we will discuss specific times cisco. Why? cisco router for a lot of wear and many other products used for the standard.

More about the routing
The data from the device connected to the Internet in the form of datagrams sent, that the data packet is defined by the IP. Datagram has a destination address of data packets; examine Internet Protocol addresses to deliver datagrams from the original device to purposes device. If the datagram destination address is a network with the original device, datagram delivered directly to purposes device. If it turns out there is no datagram destination address on the same network, datagrams delivered to the correct router (the best available router).

IP Router (commonly called routers only) are devices that perform the function of an IP datagram proceed on network layer. Routers have more than one network interface and can continue datagram from one interface to another interface. For each datagram is received, the router checks to see if the datagram is indeed directed to it. If it appears directed to the router, datagrams delivered to the transport layer.

If the datagram is not addressed to the router, which will be examined is possessed forwarding table to decide where the datagram should be addressed. Forwarding table is a table consisting of a pair of IP addresses (the address of the host or network address), the following router address, and exit interface datagram.

If you do not find a single line in the appropriate forwarding table with the destination address, the router will give the message to the sender that the address in question can not be achieved. This incident could analogy with the message "return to sender" on mail. A router can also tell that router is not the best router for a purpose, and recommend the use of other routers. With the third feature of the router, the hosts on the Internet can be interconnected.

Static and Dynamic
In general, routing coordination mechanisms can be divided into two categories: static routing and dynamic routing. In static routing, forwarding entries in the router table is filled and manually deleted, while in the dynamic routing is done through routing protocols change. Static routing is the simplest routing arrangements can be done on a computer network. Using pure static routing in a network means to fill each entry in the forwarding table at each router in the network.

The use of static routing in a small network of course not a problem, just a few entries that need to be filled in on each router forwarding table. But you can certainly imagine what if must complete forwarding table at each router in the network number is not a little big. Especially if you are asked to fill in entries over the total routers on the Internet abound and continue to improve every day. Absolutely hassle at all!

Dynamic routing is the method used to release the obligation to fill forwarding table entries manually. Organizing routing protocol router-router so that it can communicate with one another and keep each other routing information that may change the content forwarding table, hanging network conditions. In this way, the routers knows the network state final and was able to continue datagrams in the right direction.

Interior Routing Protocol
In the early 1980s the Internet is limited to the ARPANET, Satnet (ARPANET extension that uses satellite), and several local network connected via gateway. In the process, the nature of the Internet requires a hierarchical structure to anticipate the network has to be great. Then broken up into several Internet Autonomous System (AS) and currently consists of thousands of U.S. Internet. Each AS has a mechanism of information exchange and routing own collection.

Protocol used to exchange routing information in the U.S. classified as an interior routing protocol (IRP). Revenue collection routing information is then communicated to the other in the form of U.S. reachability information. Reachability information issued by a U.S. with information about the networks that can be accessed through the U.S. and became a U.S. indicator connect to the Internet. Delivery of inter-AS reachability information is done using a protocol that is classified as exterior routing protocol (ERP).

IRP are made standard on the Internet to date is the Routing Information Protocol (RIP) and Open Shortest Path First (OSPF). In addition to this there is also a second protocol routing protocols that are proprietary but widely used on the Internet, that the Internet Gateway Routing Protocol (IGRP) from Cisco Systems. IGRP protocol then expanded into Extended IGRP (EIGRP). Above all routing protocols use metrics as a basis to determine the best path can be reached by the datagram. Metric associated with the "cost" of the each link, which can be either throughput (speed of data), delay, cost, connectivity and reliability of the link.

I. Routing Information Protocol

RIP (the acronym is read as rip) included in the distance-vector protocol, a very simple protocol. Distance-vector protocol is often also called Bellman-Ford protocol, because it is the shortest distance calculation algorithm by RE Bellman, and Undescribed in the form of distributed first-time algorithm by Ford and Fulkerson.

Each router with distance-vector protocol when first run only know how to routing to itself (for local information) and do not know they are on the network topology. Then do local router sends information in the form of distance-vector to all the links that are connected directly to it. Router that receives information calculate distance-vector routing, distance-vector added to place the link metric information is received, and put it in the forwarding table entry if considered the best band. Routing information after the addition of another metric then sent across the router interface, and is performed every predetermined time. So on until around the routers in the network know the network topology.

Distance-vector protocol has a weakness that can be seen when the available network link failure. Two possible failures that may occur is the effect of bounce and count-up-not-to (counting to infinity). Bounce effects may occur in networks that use a different metric at least a link. Broken link can cause routing loops, so that datagrams that pass certain links only circling between two routers (bounce) until age (time to live) datagram is finished.

Calculated-up-not-to be due to late routers let you know that a link failure. This delay causes the router must send and receive distance-vector and metric calculates the maximum reach distance-vector metrics are achieved. Link after the break set distance-vector to the maximum metric. At the time this happened metrics routing loops, even for a longer time than in the event of bounce effect.

RIP does not adopt a distance-vector protocol so alone, but by doing some additions to the algorithm so that routing loops that occur can be minimized. Split horizon is used to minimize the effects of RIP bounce. Use split horizon principle is simple: if node A relay datagrams to destination X through node B, then B does not make sense for to achieve X by A. So there is no need to tell B that X is B by A.

To prevent the case count-up-not-to, using the method Triggered RIP Update. RIP has a timer to know when the router should be back to give routing information. If there is a change in the network, while the timer has not been exhausted, the router must still send routing information as triggered by the change (triggered updates). Thus, a router-router in the network can quickly find out the changes that occur and minimize the possibility of routing loops occur.

RIP which is defined in RFC-1058 uses metric between 1 and 15, whereas 16 is considered as not-to. With distance-vector Route 16 is not included in the forwarding table. These limits prevent 16 metric calculates the time-until-not-to for too long. RIP packets normally sent every 30 seconds or faster if there triggered updates. If in 180 seconds a route is not updated, the router route entry is removed from the forwarding table. RIP does not have information on each subnet route. Router must consider each route received has the same subnet with the router's subnet. Thus, RIP does not support Variable Length Subnet Masking (VLSM).

RIP Version 2 (RIP-2 or RIPv2) is able to produce some improvement over RIP, namely support for VLSM, use authentication, provide the following information hop (next hop), and multicast. Addition information on each route subnet mask making routers should not assume that the routes have the same subnet mask subnet mask applied to it.

RIP-2 also uses authentication to be able to know where the routing information that can be trusted. Authentication is required in routing protocol to make the protocol becomes more peaceful. RIP-1 does not use authentication so that people can give false routing information. Next hop information in RIP-2 is used by routers to inform but to achieve a route does not pass through the router route that gives information, but other routers. Application of the following hops usually in border inter-AS.

RIP-1 use broadcast addresses to send routing information. As a result, the packet is received by all hosts in the subnet and add the host workload. RIP-2 can send multicast packets using the IP so not all hosts need to receive and process routing information. Only use router-router receives RIP-2 routing information without the need to interrupt other hosts in the subnet.

RIP is a simple routing protocol, and is the reason why most RIP implemented in the network. Arranging routing using RIP uncomplicated and gives results quite acceptable, if a rare occurrence over the network link failure. Even so, for large and complex networks, RIP may not be enough. In this condition, the RIP routing calculations often require a long time, and result in a routing loop. For such networks, most of which use the computer network specialist protocol in the link-state group

II. Open Shortest Path First (OSPF)
Link-state technology developed in the ARPAnet to produce a distributed protocol that is far better than distance-vector protocols. Instead of exchanging distance (distance) to the destination, each router in the network has a network map that can be updated quickly after each topology change. This map is used to calculate a more accurate route of using distance-vector protocol. The development of this technology eventually produce protocols Open Shortest Path First (OSPF) developed by the IETF for use on the Internet. Even now the Internet Architecture Board (IAB) have recommended RIP OSPF as a substitute.

Link-state routing principle is very simple. As a substitute for calculating route "best" dis way, all routers have a network map and calculate all the best route from this map. Network map is stored in a database and each record in a database is said that a link in the network. Record-record is sent by a router that is connected directly to each link.

Because each router must have a network map that depicts the final condition of the complete network topology, every change in the network should be followed by a change in the link-state database located on each router. They detect link status change will alter the database router link-state router, then the router to send the change to the other router-router.

A protocol used to send this change should be fast and reliable. This is accomplished by flooding protocol. In the flooding protocol, the messages sent are changes from a database and message token number. By simply sending a database change, the time required for sending and processing messages are less than send the entire contents of the database. Message token number needed to know whether a received message is newer than that found in the database. This token number handy in case of a broken link to be connected again.

At the moment there is a broken link and network became separated, the second database into different parts of the network. When a broken link is alive again, databases in all routers must be equal. This data base will not return the same by sending a link-state message only. Equalization process on the router database called neighbors turn adjacency. Two adjacent routers when neighbors called the link-state database has the same second. In this process both routers are not interchangeable because the database may take a long time.

The process consists of two adjacency turn 1 phase, second router exchanging data base description is a summary from a database maintained by each router. Each router then compares the received description database with the database that you have. In the second phase, each router is asking neighbors to send record-record different databases, namely when the router does not have a record, or the number of records that are owned massage is smaller than the one sent by the description of the database. After this process, the router can update multiple records and then sent to another router-router through flooding protocol.

Link-state protocol is better than distance-vector protocol caused by several things: the time it takes to converge more quickly, and more importantly, this protocol does not produce routing loops. This protocol supports the use of multiple metrics at once. Throughput, delay, cost, and reliability are metrics commonly used in the network. In addition, this protocol can produce many lines to a destination. Suppose router A has two bands with the same metric to host B. Protocol can enter into the second band router capable of forwarding table to split the load between the lines.

Plan OSPF uses a link-state protocol with some additional functionality. Added functions among others supports multi-access networks, such as X.25 and Ethernet, and divide large networks Otis certain areas.

Has been described above that each router in a link-state protocol to form adjacency with the neighbor routers. On multi-access networks, each neighbor can be more than one router. In situations like this, every router in the network to form adjacency with every other router, and this is not efficient. OSPF adjacency to improve efficiency by introducing the concept of designated routers designated routers and backup. All adjacent routers need only to the designated router, so only designated router adjacent to all other routers. Designated router will take over the functions of the proposed designated router fails.

The first step in a multi-access network is choosing designated router and recommendations. This selection is included in the protocol, the OSPF protocol to discover neighbors routers in each link. After the election, then the routers new form adjacency with the designated router and recommendations. Each network change occurs, the router uses to send messages to the designated router flooding protocols, and the designated router that is sending the message to the other routers in the router-link.

Designated routers proposal also listen for messages sent to the designated router. If the designated router fails, the proposal then became the new designated router elected designated router and a new proposal. Because the new designated routers adjacent to the other, not to do the process of equalization of databases that require such a long time.

In a large network data base course takes big ones to keep the network topology. This leads to the need for greater router memory and computation time of a longer route. In anticipation of this, OSPF uses the concept of area and the backbone. Network is divided into a number of areas connected to the backbone. Each area is considered as its own network and routers therein only need a network topology map in that area. Routers located in the border area between just send a summary of the links that are found in the area and do not send a topology area to another area. Thus, the route calculation becomes more moderate.

Simplicity vs Ability
We have seen a glimpse of how RIP and OSPF work. Each routing protocol has its advantages and disadvantages of each. RIP protocol is very simple and easily implemented but can cause routing loops. OSPF protocol is a protocol that is more complicated and better than RIP but requires great memory and CPU time.

In many places there is also using a combination of static routing, RIP, RIP-v2, and OSPF. As a result of this network show that the administration of static routing far more time consuming than dynamic routing. Observations on dynamic routing protocols RIP also show that using a larger bandwidth and greater than OSPF network, bandwidth used increases the greater the RIP. So, if you're designing the TCP / IP network, great course OSPF routing protocol is the right choice.