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12778 Ping Traceroute

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    Understanding the Ping and Traceroute Commands Contents Introduction Prerequisites  Requirements Components Used  Conventions  Background Information The Ping Command Why Can't I Ping?  Routing Issue Interface Down Access-list Command  Address Resolution Protocol (ARP) Issue Delay Correct Source Address High Input Queue Drops  The Traceroute Command Performance Use the Debug Command Cisco Support Community - Featured Conversations Related Information  Introduction This document illustrates the use of the ping  and traceroute  commands. With the aid of some debug  commands, this document captures a more detailed view of how these commands work. Note: Enabling any debug  commands on a production router may cause serious problems. We recommend that you carefully read the Use the Debug Command  section before you issue debug  commands. Prerequisites Requirements TAC Notice:  What's Changing on TAC Web   Help us help you. Please rate this document. ExcellentGood AverageFair Poor  This document solved my problem. YesNoJust browsing Suggestions for improvement:  (256 character limit)     Send  There are no specific requirements for this document. Components Used This document is not restricted to specific software and hardware versions. The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command. Conventions For more information on document conventions, refer to the Cisco Technical Tips Conventions. Background Information In this document, we use the basic configuration shown below as a basis for our examples: The Ping Command The ping  command is a very common method for troubleshooting the accessibility of devices. It uses a series of Internet Control Message Protocol (ICMP) Echo messages to determine:  Whether a remote host is active or inactive.  The round-trip delay in communicating with the host.  Packet loss. The ping  command first sends an echo request packet to an address, then waits for a reply. The ping is successful only if:  the echo request gets to the destination, and  the destination is able to get an echo reply back to the source within a predetermined time called a timeout. The default value of this timeout is two seconds on Cisco routers. For all the options about this command, see Ping under Troubleshooting Commands. The TTL value of a ping  packet cannot be changed.  Here is an output example showing the ping  command after enabling the debug ip packet detail  command: Warning: Using the debug ip packet detail  command on a production router can cause high CPU utilization. This may result in a severe performance degradation or a network outage. We recommend that you carefully read Use the Debug Command  before issuing debug  commands. Router1# debug ip packet detail IP packet debugging is on (detailed) Router1#  ping 12.0.0.2   Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 12.0.0.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms Router1#  Jan 20 15:54:47.487: IP: s=12.0.0.1 (local), d=12.0.0.2 (Serial0), len 100, sending  Jan 20 15:54:47.491: ICMP type=8 , code=0 !--- This is the ICMP packet 12.0.0.1 sent to 12.0.0.2. !--- ICMP type=8 corresponds to the echo message.  Jan 20 15:54:47.523: IP: s=12.0.0.2 (Serial0), d=12.0.0.1 (Serial0), len 100, rcvd 3  Jan 20 15:54:47.527: ICMP type=0 , code=0 !--- This is the answer we get from 12.0.0.2. !--- ICMP type=0 corresponds to the echo reply message. !--- By default, the repeat count is five times, so there will be five !--- echo requests, and five echo replies.  The table below lists possible ICMP-type values. ICMP Type Literal 0 echo-reply 3 destination unreachable code 0 = net unreachable 1 = host unreachable 2 = protocol unreachable 3 = port unreachable 4 = fragmentation needed and DF set  The table below lists the possible output characters from the ping facility: 5 = source route failed 4 source-quench 5 redirect code 0 = redirect datagrams for the network 1 = redirect datagrams for the host 2 = redirect datagrams for the type of service and network 3 = redirect datagrams for the type of service and host 6 alternate-address 8 echo 9 router-advertisement 10 router-solicitation 11 time-exceeded code 0 = time to live exceeded in transit 1 = fragment reassembly time exceeded 12 parameter-problem 13 timestamp-request 14 timestamp-reply 15 information-request 16 information-reply 17 mask-request 18 mask-reply 31 conversion-error 32 mobile-redirect Character Description ! Each exclamation point indicates receipt of a reply. . Each period indicates the network server timed out while waiting for a reply. U A destination unreachable error PDU was
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