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Network Diagnostic Tools
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IP matching is only performed against ARP, IPv4 or IPv6 headers and not in encapsulated packets or ICMP
payloads.
If capturing too much, some packets may be lost.
13.3.4. Packet types
The capture can collect different types of packets depending on where the capture is performed. All of these
are presented as Ethernet frames, with faked Ethernet headers where the packet type is not Ethernet.
Table 13.2. Packet types that can be captured
Type
Notes
Ethernet
Interface based capture contains the full Ethernet
frame with any VLAN tag removed.
IP
IP only, currently not possible to capture at this level.
An Ethernet header is faked.
PPP
PPP from the protocol word (HDLC header is ignored
if present). An Ethernet header is faked and also a
PPPoE header. The PPPoE header has the session
PPPoE ID that is the local end L2TP session ID.
The faked protocol header has target MAC of 00:00:00:00:00:00 and source MAC of 00:00:00:00:00:01 for
received packets, and these reversed for sent packets.
13.3.5. Snaplen specification
The
snaplen
argument specifies the maximum length captured, but this applies at the protocol level. As such
PPP packets will have up to the
snaplen
from the PPP protocol bytes and then have fake PPPoE and Ethernet
headers added.
A
snaplen
value of 0 has special meaning - it causes logging of just IP, TCP, UDP and ICMP headers as
well as headers in ICMP error payloads. This is primarily to avoid logging data carried by these protocols.
13.3.6. Using the web interface
The web form is accessed by selecting the "Packet dump" item under the "Diagnostics" main-menu item. Setup
the dump parameters with reference to Table 13.1 and click the "Dump" button. Your browser will ask you to
save a file, which will take time to save as per the timeout requested.
13.3.7. Using an HTTP client
To perform a packet dump using an HTTP client, you first construct an appropriate URL that contains standard
HTTP URL form-style parameters from the list shown in Table 13.1. Then you retreive the dump from the
FB6000 using a tool such as
curl
.
The URL is
http://<FB6000
IP
address
or
DNS
name>/pcap?
parameter_name=value[¶meter_name=value ...]
The URL may include as many parameter name and value pairs as you need to completely specify the dump
parameters.
Packet capturing stops if the output stream (HTTP transfer) fails. This is useful if you are unable to determine
a suitable timeout period, and would like to run an ongoing capture which you stop manually. This is achieved
by specifying a very long duration, and then interrupting execution of the HTTP client using Ctrl+C or similar.
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