Overview

Welconcerned the civilization of routing. In the next few chapters, we will certainly look at just how packets discover their method in netfunctions through routers. In this chapter, we will learn static routing.

You are watching: Explain why the route to the 192.168.3.0/24 network on r1 is now going through r2?

Routers in our networks discover remote networks in among 2 ways;

Statically configured routesDynamic routing protocols

We will learn assorted ideas on static routes such as how to connumber static paths, just how the routing table bases its decisions, routing interencounters among other ideas.

Review

as you might already understand, the occupational of the rexternal is to forward packets from the source gadget to the destination tool. In in between there may be numerous routers. The rexternal offers a database recognized as the routing table to forward these packets.

In previous chapters, we connected a rexternal to computer and also confirmed interaction by making use of ping. However, describe the topology displayed in the exhilittle listed below.

The netjob-related above reflects a little network consisting of 3 routers and also 2 hosts. As debated previously, each connection to a router have to have its own netoccupational segment and also this is shown in the diagram.

The network administrator likewise configured R1’s and R3’s serial interdeals with as the DCE and all various other configurations are correct.

In this scenario, R1 can ping HOST A, R1 have the right to ping R2 s0/0/0 interface yet not interchallenge s0/0/1.

R3 have the right to ping HOST B, R3 deserve to ping R2’s s0/0/1 interconfront ONLY. HOST A and HOST B cannot communicate. As shown in the exhilittle below.

In this chapter, we will certainly define the reasons regarding why these two computers cannot communicate and also resolve this difficulty.

KEEP THIS TOPOLOGY IN MIND AS IT WILL BE USED THROUGHOUT THIS CHAPTER.

Directly linked networks

The routing table is the database that has information about various networks, we have shelp that these remote netfunctions might either be learnt via routing protocols or manually configured paths.

The output of the “show ip route” command also on a router, reflects the courses that a specific router deserve to reach. By default, a router will only recognize of directly connected courses.

Directly connected courses in our scenario, from R1’s perspective are the netoccupational linked to HOST A and also the netoccupational between R1 and also R2.

Since no various other configuration has actually been made on these routers, R2 and R3, have to just have straight linked paths.

The directly connected netfunctions are the just netfunctions that deserve to be reached by a specific rexternal. In our scenario, this suggests that;


The figure presented below mirrors all the straight linked networks.

Static routing

Static routes are one means we have the right to interact to remote networks. In manufacturing networks, static courses are mostly configured when routing from a particular netjob-related to a stub network-related.

stub networks are networks that can only be accessed through one suggest or one interface.

In the above scenario, the 192.168.1.0/24 and also 192.168.4.0/24 networks are stub networks. This means that for hosts in these network segments just have one method to interact via various other hosts, which is R1 and R3 for the 192.168.1.0/24 and 192.168.4.0/24 netfunctions respectively.

Understanding stub netfunctions is crucial in knowledge static routing.

The command also required to connumber a static course is shown listed below.

Router(config)# ip route (network-address) (subnet-mask) (next-hop ip address/ leave interface)

The table listed below describes the meaning of each of the parameters in the ip path command and also an example of the command also which would certainly be used on R1 to connumber a static course to R3’s LAN netoccupational (192.168.4.0/24).


ParameterMeaningexample
Ip routeState that the path being configured is a static routeIp route
Network-addressThe netjob-related address of the location network. This is the netjob-related I am trying to reach.192.168.4.0
Subnet-maskThe netjob-related address of the destination netoccupational that I am trying to reach255.255.255.0
Next off hop ip addressThis is the ip resolve of the rexternal that is connecting me to the desired network192.168.2.4
Exit interfaceThis is the departure allude interchallenge on my router that connects to the router that will take me to the preferred networks0/0/0

Refer to the exhilittle bit. Therefore to configure a static route on R1 for network 192.168.4.0/24, the command also to be issued on R1 is:

R1(config)# ip path 192.168.3.0 255.255.255.0 192.168.2.4

R1(config)# ip course 192.168.4.0 255.255.255.0 192.168.2.4

OR

R1(config)# ip route 192.168.3.0 255.255.255.0 s0/0/0

R1(config)# ip route 192.168.4.0 255.255.255.0 s0/0/0

NOTE: When configuring static routesyou need to only use either the departure interface or the following hop ip address and also not both. This will certainly be explained later on.

EXAMINE THE ROUTING TABLE ON R1:

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Highlighted inred at the bottom of the show ip route output on R1, is the static route that we simply added. The “S” at the start suggests that the routing table acquired this path as an outcome of a static route configuration.

In the braces, “1”, is the governmental distance for static routes, and “0” is the metric.

From this we deserve to assume that pings from HOST A to HOST B have to work-related. Right?

Let’s attempt a ping from HOST A TO HOST B and watch what happens.

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As you deserve to view from the exhibit above, all 4 pings to HOST B are presented as repursuit timed out. Additional, highlighted in redat the bottom, no packets were obtained by HOST B. this means that they can not communicate.

In the following area, we will certainly discover why the two hosts can not connect yet R1 was appropriately configured through a static path.

Routing table principles

Tright here are three routing table ethics that dictate how routers connect.

Principle 1:

routers forward packets based on indevelopment consisted of in their routing tables ONLY.”

R1 has 2 paths 192.168.3.0/24 which is the link in between R2 and also R3, and 192.168.4.0/24, which is the network-related on which HOST B is situated. Thus, based upon the initially principle, R1 will certainly make its forwarding decisions based on this indevelopment just. It will certainly not consult R2 or R3.Nor does it recognize whether or not those routers have actually courses to other netfunctions. As a network-related administrator, it is your responsibility to make certain that all the routers in a network recognize about remote netfunctions.

Principle 2:

” Routing information on one rexternal does not suppose that other routers in the doprimary have actually the very same indevelopment.”

R1 doesn’t recognize about the information in R2’s routing table. The same can be shelp of R2 and R3. As such, the truth that R1 has actually a route to the networks connected to R2 and R3 does not intend that R2 and also R3 have the very same indevelopment.

For example, have the right to reach the network 192.168.4.0/24 on R3 through R2. R1 does not know whether R2 deserve to reach the netjob-related connected to R3. Thus, we should configure paths from R2 to the LAN connected to R3.

Using Principle 2, we still should configure the proper routing on the other routers (R2 and R3) to make certain that they have actually courses to these 3 netfunctions.

Principle 3:

“Routes on a router to a remote netoccupational carry out not expect that the remote router has actually rerevolve paths.”

This principle implies that as soon as a route is configured on one rexternal, the remote rexternal need to be configured through a return course. In our networks, most of the interaction is bidirectional, this suggests that for every message we sfinish, a reply is intended.

If we usage the analogy of the write-up office, it would certainly be favor sending a letter without a return resolve. The recipient cannot reply to a letter without a rerevolve resolve, and the postman would not know wbelow to sfinish the letter.

In our scenario, this implies that, as soon as we connumber a route to netoccupational 192.168.4.0/24 on R1, we have to connumber a route on the remote routers that leads to the LANs connected to R1.

Using Principle 3 as guidance, we will configure appropriate static routes on the various other routers to make certain they have paths back to the 192.16.1.0/24 network.

Applying the principles:

In this scenario, we have to apply all the three values on all the routers so that the static courses can occupational.

Principle 1

R1 knows exactly how to acquire to network-related 192.168.3.0/24, and also network-related 192.168.4.0/24, but, R2 and also R3 carry out not know exactly how to acquire tbelow. As such, we should configure a static path on R2 so that it deserve to recognize just how to get to 192.168.4.0/24.

Principle 2

We configured a static route on R1, but, this does not intend that R2 knows a path to 192.168.4.0/24 netoccupational. As such this router demands to understand about that netoccupational.

Principle 3

Even though R1 and also R2 have actually a path to netjob-related 192.168.4.0, a ping would certainly still fail bereason both R2 and also R3 would not know just how to acquire to R1. As such, we should connumber a course that gets ago to netoccupational 192.168.1.0/24 on R1.in this instance we are utilizing the next-hop ip address on both R2 and also R3.

From this. We deserve to now make the important configurations on all the routers to make communication between HOST A and also HOST B feasible.

On rexternal R2:

R2(config)# ip course 192.168.1.0 255.255.255.0 192.168.2.3

R2(config)# ip path 192.168.4.0 255.255.255.0 192.168.3.3

On router R3:

R3(config)# ip path 192.168.1.0 255.255.255.0 192.168.3.4

R3(config)# ip course 192.168.4.0 255.255.255.0 192.168.3.4

When all the configurations have actually been made on all the three routers, interaction in between HOST A and HOST B have to be feasible. The number below mirrors the routing tables of all the three routers, the static paths have actually been highlighted in red.

R1:

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R2:

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R3:

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As an outcome of this output. We need to be able to ping from HOST A to HOST B. the output listed below shows the results of the ping from HOST A to HOST B.

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The output reflects that tright here are replies coming from HOST B which has the ip deal with 192.168.4.2, the highlighted section in red reflects that 4 packets were sent out and also all 4 were received by HOST B, with 0% loss.

Because of this, we have actually successfully configured static routing on the routers.

Resolving the next- hop ip address

Suppose we configured R2 via the next-hop ip address not an leave interchallenge, just how would certainly the router understand which interchallenge to sfinish the packets through?

Refer to the output of the present ip course command also on R2, listed below.

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When the router desires to sfinish a packet to the 192.168.1.0 network, it will certainly look at the routing table.

There is a route to that netoccupational using 192.168.2.3. Then the rexternal checks to view whether it has an interconfront that to the 192.168.2.3 network-related. In this scenario, that would certainly be the netjob-related highlighted in blue. The exit interchallenge is serial 0/0/0.

Routes that only have actually the next-hop ip resolve and no departure interdeals with, should have actually resolve the next hop ip resolve making use of a path on their routing table that connects to the remote netjob-related.

In most cases, the course that the following hop is readdressed to is usually a straight linked network.

Because of this, this is generally an concern, since the router hregarding process a packet twice before it deserve to recognize wbelow to forward it. This is recognized as a recursive lookup.

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It is recommended that static courses have an departure interchallenge as opposed to the next hop ip attend to.

Overview and also default routes

Suppose a rexternal has actually even more than 1 LAN linked to it. It would certainly be more helpful to usage an deal with that covers all the LANS, and connumber 1 static course. Take this scenario, R1 has 5 LANs linked to it;