CCNA Routing & Switching: Troubleshooting Connectivity

Imagine that you work as a customer support rep (CSR) fielding calls from users about problems. A user left a message stating that he couldn’t connect to a server. You could not reach him when you called back, so you did a series of pings from that host’s default router, using some of the problem isolation strategies described in Chapter 4. And at the end of those pings, you think the problem exists somewhere between the user’s device and the default router-for instance, between router R1 and host A, as shown in Figure 5-1.
Figure 5-1
Figure 5-1. Focus of the Discussions in This Section of the Chapter
This first major section of the chapter focuses on problems that can occur on hosts, their default routers, and between the two. To begin, this section looks at the host itself, and its four IPv4 settings, as listed in the figure. Following that, the discussion moves to the default router, with focus on the LAN interface, and the settings that must work for the router to serve as a host’s default router.
Root Causes Based on a Host’s IPv4 Settings
A typical IPv4 host gets its four key IPv4 settings in one of two ways: either through static configuration or by using DHCP. In both cases, the settings can actually be incorrect. Clearly, any static settings can be set to a wrong number just through human error when typing the values. More surprising is the fact that the DHCP can set the wrong values: The DHCP process can work, but with incorrect values configured at the DHCP server, the host can actually learn some incorrect IPv4 settings.
This section first reviews the settings on the host, and what they should match, followed by a discussion of typical issues.
Ensure IPv4 Settings Correctly Match
Once an engineer thinks that a problem exists somewhere between a host and its default router, the engineer should review of the host’s IPv4 settings versus the intended settings. That process begins by guiding the user through the GUI of the host operating system or by using command-line commands native to host operating systems, such as ipconfig and ifconfig. This process should uncover obvious issues, like completely missing parameters, or if using DHCP, the complete failure of DHCP to learn any of the IPv4 settings.
If the host has all its settings, the next step is to check the values to match them with the rest of the internetwork. The Domain Name System (DNS) server IP address-usually a list of at least two addresses-should match the DNS server addresses actually used in the internetwork. The rest of the settings should be compared to the correct LAN interface on the router that is used as this host’s default router. Figure 5-2 collects all the pieces that should match, with some explanation to follow.
Figure 5-2

[@royalshersingh9980]

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[@wajeehghouri3995]

really like his informative videos! i don't care about accent as long as I can understand the speaker what he is trying to convey !
thanks again for this knowledge share, really appreciated!

[@BetteBalterZen]

Very good video. Maybe a bit too fast for new learners but still very good. Thumps up from me.

[@Satendrayadav-wk6hc]

Very helpful 👍👍👍👍

[@mrshiv3166]

This video is class. I want a video where these commands are run on a real router and not cisco packet tracer :)
Best Regards.

[@arshidrashid598]

very well explained videos thanks sikandar bro. i have a question if u can provide those slides that u make to explain its gonna be really helpful. or if there is ant link that we can download. once again thanks alot for posting these videos free. you are spreading light of education free a very good source for sadqa e jaria bro thumbs up :)

[@praveenrachhu6486]

Thanks❤

[@poojajaiswal4699]

Two routers are connected, Ospf is enabled but link is down, what are the specific methods to link up, anyone can ??

[@MrThemilo209]

When access port port security triggers, will it show up as administratively down in a show ip interface brief?

[@prakruthigowda1825]

hello Team, When i try to configure IP to the router in the int f0/0 as 192.168.1.1 its taking, on the other hand, if i configure the ip for the same router int f0/1 as 192.168.2.1 , its throwing me error as overlaps with FE 0/0. Please help me in understanding

[@SAHIL-xm4hy]

Because 192 is class C network. We can not configure same network in two different ports of Routers.

[@sailoo.banwada8426]

Super

[@RaviSharma-rs5hj]

Classic Video

[@TANVEERKHAN-zh8ti]

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[@kadugomes7114]

Your videos are very useful, but the accent is loo much exagerated, unfurtanely.