1.3.a (ii) ping, traceroute with extended options

1.3.a Use IOS troubleshooting tools
1.3.a (i) debug, conditional debug
1.3.a (ii) ping, traceroute with extended options
1.3.a (iii) Embedded packet capture
1.3.a (iv) Performance monitor

http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-121-mainline/12778-ping-traceroute.html

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.

The ping Command
The ping (Packet InterNet Groper) command is a very common method for troubleshooting the accessibility of devices. It uses two Internet Control Message Protocol (ICMP) query messages, ICMP echo requests, and ICMP echo replies to determine whether a remote host is active. The ping command also measures the amount of time it takes to receive the echo reply.
The ping command first sends an echo request packet to an address, and then it 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 of the ping within a predefined time interval.

The Extended ping Command

When a normal ping command is sent from a router, the source address of the ping is the IP address of the interface that the packet uses to exit the router. If an extended ping command is used, the source IP address can be changed to any IP address on the router. The extended ping is used to perform a more advanced check of host reachability and network connectivity. The extended ping command works only at the privileged EXEC command line. The normal ping works both in the user EXEC mode and the privileged EXEC mode. In order to use this feature, enter ping at the command line and press Return. You are prompted for the fields as given in the ping Command Field Descriptions section of this document.

The traceroute Command
Where ping can be used to verify connectivity between devices, the traceroute command can be used to discover the paths packets take to a remote destination, as well as where routing breaks down.
The purpose behind the traceroute command is to record the source of each ICMP "time exceeded" message in order to provide a trace of the path the packet took to reach the destination.
The device that executes the traceroute command sends out a sequence of User Datagram Protocol (UDP) datagrams, each with incrementing Time-To-Live (TTL) values, to an invalid port address (Default 33434) at the remote host.
First, three datagrams are sent, each with a TTL field value set to 1. The TTL value of 1 causes the datagram to "timeout" as soon as it hits the first router in the path. This router then responds with an ICMP "time exceeded" message which indicates that the datagram has expired.
Next, three more UDP messages are sent, each with the TTL value set to 2. This causes the second router in the path to the destination to return ICMP "time exceeded" messages.
This process continues until the packets reach the destination and until the system that originates the traceroute receives ICMP "time exceeded" messages from every router in the path to the destination. Since these datagrams try to access an invalid port (Default 33434) at the destination host, the host responds with ICMP "port unreachable" messages that indicate an unreachable port. This event signals the traceroute program to finish.
Note: Make sure you have not disabled the ip unreachable command using no ip unreachables under any VLAN. This command makes the packet discard without sending any ICMP error message. In this case, traceroute does not work.

The Extended traceroute Command

The extended traceroute command is a variation of the traceroute command. An extended traceroute command can be used to see what path packets take in order to get to a destination. The command can also be used to check routing at the same time. This is helpful for when you troubleshoot routing loops, or for when you determine where packets are getting lost (if a route is missing, or if packets are being blocked by an Access Control List (ACL) or firewall). You can use the extended ping command in order to determine the type of connectivity problem, and then use the extended traceroute command in order to narrow down where the problem occurs.
A "time exceeded" error message indicates that an intermediate communication server has seen and discarded the packet. A "destination unreachable" error message indicates that the destination node has received the probe and discarded it because it could not deliver the packet. If the timer goes off before a response comes in, trace prints an asterisk(*). The command terminates when any of these happens:

• the destination responds
• the maximum TTL is exceeded
• the user interrupts the trace with the escape sequence
  Note: You can invoke this escape sequence when you simultaneously press Ctrl, Shift and 6.

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