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.
Laptop Battery 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.
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Thinkpad 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.
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Microsoft 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.
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Laptop Computers R1#debug ip packet
level certification. or user requirements. They should also be able to develop and test a prototype network that validates the design to the user's satisfaction. Candidates must possess a valid CCNA or CCDA certification prior to taking these exams. For rmation on the CCDP program, visit the related page on the Cisco Web site.
Laptop Computer IP packet debugging is on
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Desktop Computer
R1#ping 22.2.2.2
Notebooks Type escape sequence to abort.
Lenovo Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:
Hard Drive 3d23h: IP: s=1.1.1.1 (local), d=22.2.2.2, len 100, unroutable.
Travelstar R1#undebug all
Gateway All possible debugging has been turned off
Laptop Parts 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.
Software R1#ping 22.2.2.2
Hard Drives Type escape sequence to abort.
Electronics Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:
Canon U.U.U
Desktop Pc Success rate is 0 percent (0/5)
Desktop Computers 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.
Think Pad R1#debug ip packet
Repair IP packet debugging is on
Data Recovery R1#ping 22.2.2.2
Cisco Type escape sequence to abort.
Keyboard Sending 5, 100-byte ICMP Echos to 22.2.2.2, timeout is 2 seconds:
Monitor 3d23h: IP: s=172.12.123.1 (local), d=22.2.2.2 (Serial0), len 100, sending
Desktop R1#traceroute 22.2.2.2
Infosys Type escape sequence to abort.
Refurbished Laptops Tracing the route to 22.2.2.2
Wipro 1 172.12.123.2 36 msec 36 msec 36 msec
Lap Top 2 172.12.123.2 !H * !H
Refurbished R1#undebug all
Memory All possible debugging has been turned off
Intel 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.
As400 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!
Averatec
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