Tracing Unicast Routes from the J-Web Interface

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 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.

Alternatively, you can use the CLI traceroute command to generate the list.

This section contains the following topics:

Using the J-Web Traceroute Tool
Traceroute Results and Output Summary

Using the J-Web Traceroute Tool

To use the traceroute tool:

Select Troubleshoot>Traceroute.
Next to Advanced options, click the expand icon (see Figure 29).
Enter information into the Traceroute page, as described in Table 152.
The Remote Host field is the only required field.
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.
Table 153 summarizes the output fields of the display.
To stop the traceroute operation before it is complete, click OK while the results of the traceroute operation are being displayed.

Figure 29: Traceroute Page

Image s030256.gif

Table 152: Traceroute Field Summary

Field	Function	Your 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 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 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 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.

Traceroute Results and Output Summary

Table 153 summarizes the output in the traceroute display. If the device receives no responses from the destination host, review the list after Table 153 for a possible explanation.

Table 153: J-Web Traceroute Results and Output Summary

Field	Description
hop-number	Number of the hop (router) along the path.
host	Hostname, if available, or IP address of the router. If the Don't Resolve Addresses check box is selected, the hostname is not displayed.
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.

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.