You can create, download, and upload TCP capture files in the Reports > Diagnostics: TCP Dumps page.
Capture files contain summary information for every internet packet received or transmitted on the interface to help diagnose problems in the system.
RiOS provides an easy way to create and retrieve multiple capture files from the Management Console. You can create capture files from multiple interfaces at the same time, limit the size of the capture file, and schedule a specific date and time to create a capture file. Scheduling and limiting a capture file by time or size allows unattended captures.
RiOS supports remote capture analysis using the SteelCentral Packet Analyzer on capture files created and stored on the appliance without transferring the entire packet capture across the network. The appliance includes this functionality as Embedded SteelCentral NetShark. Embedded SteelCentral NetShark software enables on-demand packet capture on appliances at remote sites, and control and analysis of packet captures on remote appliances directly from Packet Analyzer. You can use Embedded SteelCentral NetShark to drill down to deliver microlevel flow resolution for analysis using Riverbed's XML-based protocol on top of an HTTPS connection for transferring data to Packet Analyzer. You do not need to transfer full packets until you need them.
Note: You cannot upload a capture file to the appliance using Packet Analyzer.
The top of the TCP Dumps page displays a list of existing capture files and the bottom of the page displays controls to create a capture file. The bottom of the page also includes the capture files that are currently running, and controls to create a trigger that stops a capture when a specific event occurs. The Running Capture Name list includes captures running at a particular time. It includes captures started manually and also any captures that were scheduled previously and are now running.
To capture TCP dumps
1. Choose Reports > Diagnostics: TCP Dumps to display the TCP Dumps page.
Figure: TCP Dumps page
2. Complete the configuration as described in this table.
Control
Description
Add a New TCP Dump
Displays the controls for creating a TCP trace dump.
Capture Name
Specify the name of the capture file. The default filename uses this format:
<hostname>_<interface>_<timestamp>.cap
Where <hostname> is the hostname of the Edge, <interface> is the name of the interface selected for the trace (for example, lan0_1, wan0_1), and <timestamp> is in the yyyy-mm-dd-hh-mm-ss format.
If this trace dump relates to an open Riverbed Support case, specify the capture filename case_<number> where <number> is your Riverbed Support case number. For example, case_12345.
Note: The .cap file extension is not included with the filename when it appears in the capture queue.
Endpoints
Specify IP addresses and port numbers to capture packets between them:
IPs - Specify IP addresses of endpoints on one side. Separate multiple IP addresses using commas. You can enter IPv6 addresses separated by commas. The default setting is all IP addresses.
Ports - Specify ports on one side. Separate multiple ports using commas. The default setting is all ports.
—and—
IPs - Specify IP addresses of endpoints on the other side. Separate multiple IP addresses using commas. You can enter IPv6 addresses separated by commas. The default setting is all IP addresses.
Ports - Specify ports on the other side. Separate multiple ports using commas. The default setting is all ports.
To capture traffic flowing in only one direction or to enter a custom command, use the tcpdump command. For details, see the Riverbed Command-Line Interface Reference Manual.
Capture Interfaces
Captures the TCP trace dump on the selected interface(s). You can select all interfaces or a base, in-path, data, or miscellaneous interface. The default setting is none. You must specify a capture interface.
If you select several interfaces at a time, the data is automatically placed into separate capture files.
Capture Parameters
These parameters let you capture information about dot1q VLAN traffic. You can match traffic based on VLAN-tagged or untagged packets, or both. You can also filter by port number or host IP address and include or exclude ARP packets. Select one of these parameters for capturing VLAN packets:
• Capture Untagged Traffic Only - Select this option for the following captures:
– All untagged VLAN traffic.
– Untagged 7850 traffic and ARP packets. You must also specify or arp in the custom flags field in this page.
– Only untagged ARP packets. You must also specify and arp in the custom flags field in this page.
• Capture VLAN-Tagged Traffic Only - Select this option for the following captures:
– Only VLAN-tagged traffic.
– VLAN-tagged packets with host 10.11.0.6 traffic and ARP packets. You must also specify 10.11.0.6 in the IPs field, and specify or arp in the custom flags field in this page.
– VLAN-tagged ARP packets only. You must also specify and arp in the custom flags field in this page.
• Capture both VLAN and Untagged Traffic - Select this option for the following captures:
– All VLAN traffic.
– Both tagged and untagged 7850 traffic and ARP packets. You must also specify the following in the custom flags field in this page:
(port 7850 or arp) or (vlan and (port 7850 or arp))
– Both tagged and untagged 7850 traffic only. You must also specify 7850 in one of the port fields in this page. No custom flags are required.
– Both tagged and untagged ARP packets. You must also specify the following in the custom flags field in this page:
(arp) or (vlan and arp)
Capture Duration (Seconds)
Specify a positive integer to set how long the capture runs, in seconds. The default value is 30. Specify 0 or continuous to initiate a continuous trace. For continuous capture, we recommend specifying a maximum capture size and a nonzero rotate file number to limit the size of the TCP dump.
Maximum Capture Size (MB)
Specify the maximum capture file size in megabytes. The default value is 100. The recommended maximum capture file size is 1024 MB (1 GB).
Buffer Size
Optionally, specify the maximum number of packets allowed to queue up while awaiting processing by the TCP trace dump. The default value is 154.
Snap Length
Optionally, select the snap length value, in bytes, for the capture file or specify a custom value. The snap length equals the number of bytes the report captures for each packet. Having a snap length smaller than the maximum packet size on the network enables you to store more packets, but you might not be able to inspect the full packet content. The default value is 1518.
Select 0 for a full packet capture (recommended for CIFS, MAPI, and SSL captures).
When using jumbo frames, we recommend selecting 9018.
The default custom value is 16383.
Number of Files to Rotate
Specify how many capture files to keep for each interface before overwriting the oldest file. To stop file rotation, you can specify 0; however, we recommend rotating files, because stopping the rotation can fill the disk partition.
This control limits the number of files created to the specified number, and begins overwriting files from the beginning, thus creating a rotating buffer.
The default value is 5. The maximum value is a 32-bit integer.
Custom Flags
Specify custom flags as additional statements within the filter expression. Custom flags are added to the end of the expression created from the Endpoints fields and the Capture Parameters radio buttons (pertaining to VLANs).
If you require an “and” statement between the expression created from other fields and the expression that you are entering in the custom flags field, you must include the “and” statement at the start of the custom flags field.
Do not use host, src, or dst statements in the custom flags field. Although it is possible in trivial cases to get these to start without a syntax error, they do not capture GRE-encapsulated packets that some modes of SteelHead communications use, such as WCCP deployments or Interceptor connection-setup traffic. We recommend using bidirectional filters by specifying endpoints.
For complete control of your filter expression, use the CLI tcpdump command. For details, see the Riverbed Command-Line Interface Reference Manual.
Schedules the trace dump to run at a later date and time.
Start Date
Specify a date to initiate the trace dump in this format: yyyy/mm/dd
Start Time
Specify a time to initiate the trace dump in this format: hh:mm:ss
Add
Adds the TCP trace dump to the capture queue.
Troubleshooting
If your command results in a syntax error with an immediate or scheduled TCP dump, this message appears:
Error in tcpdump command. See System Log for details.
Review the system log to see the full tcpdump command attempt. Check the expression for issues such as a missing “and,” as well as contradictory instructions such as looking for VLAN-tagged traffic AND non-tagged traffic.
Custom flag use examples
The examples in this table focus on the custom flag entry but they rely on other fields to create a complete filter.
Filter Purpose
Custom Flag
To capture all traffic on VLAN 10 between two specified endpoints: 1.1.1.1 and 2.2.2.2
and vlan 10
To capture any packet with a SYN or an ACK
tcp[tcpflags] & (tcp-syn|tcp-ack) != 0
To capture any packet with a SYN
tcp[tcpflags] & (tcp-syn) != 0
—or—
tcp[13] & 2 == 2
To capture any SYN to or from host 1.1.1.1
and (tcp[tcpflags] & (tcp-syn) != 0)
—or—
and (tcp[13] & 2 == 2)
IPv6 custom flag use examples
The examples in this table focus on the custom flag entry, but rely on other fields to create a complete filter.
To build expressions for TCP dump, IPv6 filtering does not currently support the TCP, UDP, and other upper-layer protocol types that IPv4 does. Also, these IPv6 examples are based on the assumption that only a single IPv6 header is present.
Filter Purpose
Custom Flag
To capture all FIN packets to or from host 2001::2002
and (ip6[53] & 1!=0)
To capture all IPv6 SYN packets
ip6 or proto ipv6 and (ip6[53] & 2 == 2)
Stopping a TCP dump after an event occurs
Capture files offer visibility into intermittent network issues, but the amount of traffic they capture can be overwhelming. Also, because rotating logs is common, after a capture logs an event, the appliance log rotation can overwrite debugging information specific to the event.
RiOS makes troubleshooting easier because it provides a trigger that can stop a continuous capture after a specific log event occurs. The result is a smaller file to help pinpoint what makes the event happen.
The stop trigger continuously scans the system logs for a search pattern. When it finds a match, it stops all running captures.
To stop a capture after a specific log event
1. Choose Administration > Diagnostics: TCP Dumps to display the TCP Dumps page.
2. Schedule a capture.
Figure: TCP Dumps page - TCP Dump Stop Trigger
3. In the Pattern text box, enter a Perl regular expression (regex) to find in a log. RiOS compares the Perl regex against each new line in the system logs and the trigger stops if it finds a match.
The simplest regex is a word or a string of characters. For example, if you set the pattern to “Limit,” the trigger matches the line “Connection Limit Reached.”
Notes:
– Perl regular expressions are case sensitive.
– Perl treats the space character like any other character in a regex.
– Perl reserves some characters, called metacharacters, for use in regex notation. The metacharacters are:
{ } [ ] ( ) ^ $ . | * + ? \
You can match a metacharacter by putting a backslash before it. For example, to search for a backslash in the logs, you must enter two backslashes (\\) as the pattern.
– The pattern follows Perl regular expression syntax. For details, go to:
– You cannot change the pattern while a scan is running. You must stop the scan before changing a pattern.
– You do not need to wrap the pattern with the metacharacters to match the beginning or end of a line (^ $) or with the wildcard character (*).
4. Specify the amount of time, in seconds, to pause before stopping all running captures when RiOS finds a match. The time delay gives the system some time to log more data without abruptly cutting off the capture. The default is 30. Specify 0 for no delay; the capture stops immediately.
After a trigger has fired, the capture can stop by itself before the delay expires. For example, the capture duration can expire.
5. Click Start Scan.
When the scan stops, RiOS sends an email to all email addresses on the Administration: System Settings > Email page appearing under Report Events via Email. The email notifies users that the trigger has fired.
The page indicates “Last Triggered: Never” if a TCP Dump stop trigger has never triggered on the appliance. After the delay duration of the stop trigger, RiOS displays the last triggered time.
Before changing the Perl regular expression or amount of delay, you must first stop the process.
To stop a running scan
• Click Stop Scan to halt the background process that monitors the system logs. RiOS dims this button when the stop trigger is idling.
Stop trigger limitations
These limitations apply to the trigger:
• You cannot create a trigger to stop a specific capture; the trigger affects all running captures.
• If the search pattern contains a typo, the trigger might never find a match.
• Only one instance of a trigger can run at one time.
Viewing a TCP dump
The top of the TCP Dumps page displays a list of existing captures.
To view a capture file
1. Choose Reports > Diagnostics: TCP Dumps to display the TCP Dumps page.
2. Under Stored TCP Dumps, select the capture name to open the file.
3. Click Download to view a previously saved capture file.
4. To remove a capture file, select the check box next to the name and click Remove Selected.
To print a capture file
1. Choose Reports > Diagnostics: TCP Dumps to display the TCP Dumps page.
2. Under Download Link, select the capture filename to open the file.
3. When the file opens, choose File > Print in your web browser to open the Print dialog box.
To stop a running capture
1. Choose Reports > Diagnostics: TCP Dumps to display the TCP Dumps page.
2. Select the capture filename in the Running Capture Name list.
3. Click Stop Selected Captures.
Uploading a TCP dump
Riverbed offers a couple of ways to upload capture files to the support server for sharing with the support team while diagnosing issues.
To upload the capture file to Riverbed Support
1. In continuous mode, on the TCP Dumps page, select the running capture and click Stop Selected Captures.
For timed captures that are complete, skip to Step 2.
The capture appears as a download link in the list of Stored TCP Dumps.
2. Select the capture filename.
3. Optionally, specify a case number that corresponds to the capture. Riverbed Support recommends using a case number: for example, 194170.
To specify a URL instead of a case number, you must use the CLI. You can enter the file tcpdump upload <url> command. When you specify a URL, the capture file goes directly to the URL.
If the URL points to a directory on the upload server, it must have a trailing backslash (/).
For example:
ftp://ftp.riverbed.com/incoming/
(not ftp://ftp.riverbed.com/incoming)
The filename as it exists on the appliance will then match the filename on the upload server.
For details, see the Riverbed Command-Line Interface Reference Manual.
4. Click Upload.
Because uploading a capture file can take a while (especially when including ESXi information on an Edge), a progress bar displays the percentage of the total upload completed, the case number (if applicable), and the date and time the upload began. When the capture file finishes uploading, the date, time, and a status of either uploaded (appears in green) or failed (appears in red).
Successful uploads show the status, the case number (if applicable), and the date and time the upload finished.
For uploads that fail, an explanation, the case number (if applicable), and the upload starting date and time appear.
