Troubleshooting Traceroute

Problem

Description: You can use the traceroute diagnostic tool to display a list of routers between the device and a specified destination host. The output is useful for diagnosing a point of failure in the path from the device to the destination host, and for addressing network traffic latency and throughput problems.

The device generates the list of routers by sending a series of ICMP traceroute packets in which the time-to-live (TTL) value in the messages sent to each successive router is incremented by 1. (The TTL value of the first traceroute packet is set to 1.) In this manner, each router along the path to the destination host replies with a Time Exceeded packet from which the source IP address can be obtained.

Solution

To use the traceroute tool:

  1. Select Troubleshoot>Traceroute.
  2. Click the expand icon next to Advanced options.
  3. Enter information in the Traceroute page as described in Table 282.

    The Remote Host field is the only required field.

  4. Click Start.

    The results of the traceroute operation are displayed in the main pane. If no options are specified, each line of the traceroute display is in the following format:

    hop-number host (ip-address) [as-number]time1 time2 time3

    The device sends a total of three traceroute packets to each router along the path and displays the round-trip time for each traceroute operation. If the device times out before receiving a Time Exceeded message, an asterisk (*) is displayed for that round-trip time.

  5. Click OK to stop the traceroute operation before it is complete.

Table 282: Ping Traceroute Troubleshooting Options

Field

Function

Action

Remote Host

Identifies the destination host of the traceroute.

Type the hostname or IP address of the destination host.

Advanced Options

Don't Resolve Addresses

Determines whether or not hostnames of the hops along the path are displayed, in addition to IP addresses.

  • To suppress the display of the hop hostnames, select the check box.
  • To display the hop hostnames, clear the check box.

Gateway

Specifies the IP address of the gateway to route through.

Type the gateway IP address.

Source Address

Specifies the source address of the outgoing traceroute packets.

Type the source IP address.

Bypass Routing

Determines whether or not traceroute packets are routed by means of the routing table.

If the routing table is not used, traceroute packets are sent only to hosts on the interface specified in the Interface box. If the host is not on that interface, traceroute responses are not sent.

  • To bypass the routing table and send the traceroute packets to hosts on the specified interface only, select the check box.
  • To route the traceroute packets by means of the routing table, clear the check box.

Interface

Specifies the interface on which the traceroute packets are sent.

From the list, select the interface on which traceroute packets are sent. If you select any, the traceroute requests are sent on all interfaces.

Time-to-Live

Specifies the maximum time-to-live (TTL) hop count for the traceroute request packet.

From the list, select the TTL.

Type-of-Service

Specifies the type-of-service (ToS) value to include in the IP header of the traceroute request packet.

From the list, select the decimal value of the ToS field.

Resolve AS Numbers

Determines whether or not the autonomous system (AS) number of each intermediate hop between the device and the destination host is displayed.

  • To display the AS numbers, select the check box.
  • To suppress the display of the AS numbers, clear the check box.
Ping Traceroute Results and Output Summary

hop-number

Number of the hop (router) along the path.

host

Hostname, if available, or IP address of the router.

To suppress the display of the hostname, select the Don't Resolve Addresses check box.

ip-address

IP address of the router.

as-number

AS number of the router.

time1

Round-trip time between the sending of the first traceroute packet and the receiving of the corresponding Time Exceeded packet from that particular router.

time2

Round-trip time between the sending of the second traceroute packet and the receiving of the corresponding Time Exceeded packet from that particular router.

time3

Round-trip time between the sending of the third traceroute packet and the receiving of the corresponding Time Exceeded packet from that particular router.

Output = Complete path to the destination host not displayed

If the device does not display the complete path to the destination host, one of the following explanations might apply:

  • The host is not operational.
  • There are network connectivity problems between the device and the host.
  • The host, or a router along the path, might be configured to ignore ICMP traceroute messages.
  • The host, or a router along the path, might be configured with a firewall filter that blocks ICMP traceroute requests or ICMP time exceeded responses.
  • The value you selected in the Time Exceeded box was less than the number of hops in the path to the host. In this case, the host might reply with an ICMP error message.

For more information about ICMP, see RFC 792, Internet Control Message Protocol.

Related Documentation