Back to Home

Back to Computer and Internet

 

 

Other Great Sites

MorningValley.com All the Best Christmas stuff, from all over the net!

SpaceWeekly.com The latest Space News!

BinChat.com Learn all about Blogging!

CompuHype.com The latest Technology News!

Computer Hunter Internet Advice and Fun!

Free Monkey Search Get a free monkey with every search!

TruthIsFalse.com Every thing you know is a lie!

SciFiStar.com Your link to the Stars on the net!

[an error occurred while processing this directive]

e0s.com Who caused Sept 11 The answer is here!

CapitalDomains.com Get your own Dot Com Name!

WhoHe Do you know these Male Celebrities?

WhoShe Do you know these Female Celebrities?

Hero or Zero Vote for your favorite Hero or against a Zero!

Tips Point FREE tips and hints about everything.

UnFind Find anything related to the United Nations!

SnackSite.com Chocolate at its Best!

NextNest.com Interior Design

VibeFanClub.com Everything Automotive!

CashRoundUp.com Home Equity Resources

ClickJets.com All about Travel

HikingBin.com Recreation Resources

Computer Hunter .org Articles about almost everything!

BeyondTheBedroom.com All the Best Bed Room stuff, from all over the net!

       

Cisco CCNA / CCNP Certification: Deciphering Ping Output
 by: Chris Bryant, CCIE #12933

As you study for your CCNA and CCNP exams, particularly if you're getting hands-on practice in your home lab or rack rental service, you're going to be sending a lot of pings. As a CCNA or CCNP candidate, you know that five exclamation points (!!!!!) as a ping return indicates that you have IP connectivity to the remote destination. Five periods (.....) indicates that you do not have that connectivity.

It's not enough to know that you don't have IP connectivity to the remote device, you've got to know why. Ping is a great first step to network troubleshooting, but the results are quite limited. As a CCNA and CCNP, you've got to know how to diagnose the problem and resolve it. Just looking at the routing table is not enough - a high-powered Cisco debug, debug ip packet, can often show you exactly where the problem is.

WARNING: debug ip packet should not be run on any production router without understanding the effect of this command on your router. This command results in a lot of output and can actually lock up a router.

In this case, we'll run the command on a home lab router that cannot ping 22.2.2.2. The debug will be turned on and another ping sent.

R1#debug ip packet

IP packet debugging is on

R1#ping 22.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:

3d23h: IP: s=1.1.1.1 (local), d=22.2.2.2, len 100, unroutable.

R1#undebug all

All possible debugging has been turned off

I've edited this output for clarity; the important word is "unroutable". This indicates that the packet is not leaving the router because there is no match in the routing table for this destination. We'll configure a static default route and send the ping again.

R1#ping 22.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:

U.U.U

Success rate is 0 percent (0/5)

That output may surprise those of you who are used to getting five of the same symbol back whenever you send a ping. We got three "U"s back along with two periods. We'll now run debug ip packet and send the ping again.

R1#debug ip packet

IP packet debugging is on

R1#ping 22.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:

3d23h: IP: s=172.12.123.1 (local), d=22.2.2.2 (Serial0), len 100, sending

R1#traceroute 22.2.2.2

Type escape sequence to abort.

Tracing the route to 22.2.2.2

1 172.12.123.2 36 msec 36 msec 36 msec

2 172.12.123.2 !H * !H

R1#undebug all

All possible debugging has been turned off

Again, I've edited this output. The key word in this output is "sending", meaning that the packets are leaving the router. The ping return of "U.U.U" is a general indication that the packets are indeed being transmitted, but that a downstream router is having a problem routing the packets. Running traceroute reveals some more interesting return characters! In this case, the downstream router did not have a match for the destination in its routing table.

It's easy to concentrate on the local router when you're not getting positive ping returns. When troubleshooting this kind of issue, keep in mind the problem could be on an intermediate router and not on the local router. Use debug ip packet to make sure the packets are leaving the local router, and traceroute to determine what downstream router may have the problem. And get used to the fact that pings and traceroutes can give you some unusual-looking returns!

About The Author

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also sign up to receive a FREE CCNA and CCNP question in your inbox every day! Get your CCNA certification with The Bryant Advantage!

chris@thebryantadvantage.com

This article was posted on February 06, 2006

 

© copyright 2007 CyberCattle.com