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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
To use the traceroute tool:
- Select Troubleshoot>Traceroute.
- Next to Advanced options, click the expand icon
(see Figure 23).
- Enter information into the Traceroute page, as
described in Table 200.
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 201 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 23: Traceroute Page
Table 200: 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 201 summarizes
the output in the traceroute display. If the device receives
no responses from the destination host, review the list after Table 201 for a possible
explanation.
Table 201: 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.
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