http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_tech_note09186a00800a6057.shtml

Extended Ping and Traceroute

Source of this information: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f22.shtml

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
The ping Command
      The Extended ping Command
      ping Command Field Descriptions
      The traceroute Command
      The Extended traceroute Command
      traceroute Command Field Descriptions
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Related Information

Introduction

This document illustrates how to use the extended ping and extended traceroute commands. Standard ping and traceroute commands are covered extensively in these documents:

· Understanding the ping and traceroute Commands

· Using the traceroute Command on Operating Systems

Prerequisites

Requirements

This document requires an understanding of the ping and traceroute commands which are described in detail in the links given in the Introduction section of this document.

Components Used

The information in this document is based on these software and hardware versions:

· Cisco IOS® Software Release 12.2(10b)

· All Cisco series routers

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

Refer to Cisco Technical Tips Conventions for more information on document conventions.

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.

ping Command Field Descriptions

This table lists the ping command field descriptions. These fields can be modified with the use of the extended ping command.

Source address or interface: ethernet 0 

In this diagram, Host 1 and Host 2 are unable to ping each other. You can troubleshoot this problem on the routers in order to determine if there is a routing problem, or if one of the two hosts does not have its default gateway correctly set.

In order for the ping from Host 1 to Host 2 to succeed, each host needs to point its default gateway to the router on its respective LAN segment, or the host needs to exchange network information with the routers that use a routing protocol. If either host does not have its default gateway set correctly, or it does not have the correct routes in its routing table, it is not able to send packets to destinations not present in its Address Resolution Protocol (ARP) cache. It is also possible that the hosts cannot ping each other because one of the routers does not have a route to the subnet from which the host is sourcing its ping packets.

Example

This is an example of the extended ping command sourced from the Router A Ethernet 0 interface and destined for the Router B Ethernet interface. If this ping succeeds, it is an indication that there is no routing problem. Router A knows how to get to the Ethernet of Router B, and Router B knows how to get to the Ethernet of Router A. Also both hosts have their default gateways set correctly.

If the extended ping command from Router A fails, it means that there is a routing problem. There could be a routing problem on any of the three routers. Router A could be missing a route to the subnet of Router B's Ethernet, or to the subnet between Router C and Router B. Router B could be missing a route to the subnet of Router A's subnet, or to the subnet between Router C and Router A; and Router C could be missing a route to the subnet of Router A's or Router B's Ethernet segments. You should correct any routing problems, and then Host 1 should try to ping Host 2. If Host 1 still cannot ping Host 2, then both hosts' default gateways should be checked. The connectivity between the Ethernet of Router A and the Ethernet of Router B is checked with the extended ping command.

With a normal ping from Router A to Router B's Ethernet interface, the source address of the ping packet would be the address of the outgoing interface, that is, the address of the serial 0 interface (172.31.20.1). When Router B replies to the ping packet, it replies to the source address (that is, 172.31.20.1). This way, only the connectivity between the serial 0 interface of Router A (172.31.20.1) and the Ethernet interface of Router B (192.168.40.1) is tested.

In order to test the connectivity between Router A Ethernet 0 (172.16.23.2) and Router B Ethernet 0 (192.168.40.1), use the extended ping command. With extended ping, you get the option to specify the source address of the ping packet, as shown here.

Router A>enable

Router A#ping

Protocol [ip]:

Target IP address: 192.168.40.1

!--- The address to ping.

Repeat count [5]:

Datagram size [100]:

Timeout in seconds [2]:

Extended commands [n]: y

Source address or interface: 172.16.23.2 

!---Ping packets are sourced from this address.

Type of service [0]:

Set DF bit in IP header? [no]:

Validate reply data? [no]:

Data pattern [0xABCD]:

Loose, Strict, Record, Timestamp, Verbose[none]:

Sweep range of sizes [n]:

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 162.108.21.8, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 36/97/132 ms  

!--- Ping is successful.

Router A#

This is an example with extended commands and sweep details:

Router A>enable

Router A#ping

Protocol [ip]:

!--- The protocol name.

Target IP address: 192.168.40.1

!--- The address to ping.

Repeat count [5]: 10

!--- The number of ping packets that are sent to the destination address.

Datagram size [100]:

!--- The size of the ping packet in size. The default is 100 bytes.

Timeout in seconds [2]:

!--- The timeout interval. The ping is declared successful only if the 

!--- ECHO REPLY packet is received before this interval.

Extended commands [n]: y      

!--- You choose yes if you want extended command options 

!--- (Loose Source Routing, Strict Source Routing, Record route and Timestamp).

Source address or interface: 172.16.23.2 

!--- Ping packets are sourced from this address and must be the IP address 

!--- or full interface name (for example, Serial0/1 or 172.16.23.2).

Type of service [0]:

!--- Specifies Type of Service (ToS).

Set DF bit in IP header? [no]:

!--- Specifies whether or not the Don’t Fragment (DF) bit is to be 

!--- set on the ping packet.

Validate reply data? [no]:

!--- Specifies whether or not to validate reply data.

Data pattern [0xABCD]:

!--- Specifies the data pattern in the ping payload.  Some physical links 

!--- might exhibit data pattern dependent problems. For example, serial links 

!--- with misconfigured line coding.  Some useful data patterns to test 

!--- include all 1s (0Xffff), all 0s (0x0000) and alternating 

!--- ones and zeros (0Xaaaa).

Loose, Strict, Record, Timestamp, Verbose[none]:

!--- IP header options.

Sweep range of sizes [n]: y

!--- Choose yes if you want to vary the sizes on echo packets that are sent.

Sweep min size [36]:

Sweep max size [18024]:

Sweep interval [1]:

Sending 179890, [36..18024]-byte ICMP Echos to 162.108.21.8, timeout is 2 seconds:

!--- The count 179890 depends on the values of min sweep, 

!--- max sweep, sweep interval and repeat count. Calculations are based on: 

!--- 18024(high end of range) - 36(low end of range) = 17988(bytes in range) 

!--- 17988(bytes in range) / 1(sweep interval) = 17988 (steps in range)

!--- 17988(bytes in range) + 1 (first value) = 17989(values to be tested)

!--- 17989(values to be tested) * 10(repeat count) = 179890 (pings to be sent)

!--- In order to decrease the value, increase the sweep interval or decrease 

!--- the repeat count, or you can even decrease the difference between 

!--- Minimum and Maximum sweep size.  Based on the previous example, the 

!--- number 17890 is an expected value and tries to ping 17890 times.

Packet sent with a source address of 172.16.23.2

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Success rate is 100 percent, round-trip min/avg/max = 1/2/4 ms

!--- Ping is successful.

Router A#

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.

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.

traceroute Command Field Descriptions

This table lists the traceroute command field descriptions:

Example

Router A>enable

Router A#traceroute

Protocol [ip]:

Target IP address: 192.168.40.2   

!--- The address to which the path is traced.

Source address: 172.16.23.2

Numeric display [n]:

Timeout in seconds [3]:

Probe count [3]:

Minimum Time to Live [1]:

Maximum Time to Live [30]:

Port Number [33434]:

Loose, Strict, Record, Timestamp, Verbose[none]:

Type escape sequence to abort.

Tracing the route to 192.168.40.2

  1 172.31.20.2 16 msec 16 msec 16 msec

  2 172.20.10.2 28 msec 28 msec 32 msec

  3 192.168.40.2 32 msec 28 msec *   

!--- The traceroute is successful.

Router A#

Note: The extended traceroute command can be executed in the privileged EXEC mode only, whereas the normal traceroute command works on both the user and privileged EXEC modes.