115 lines
4.8 KiB
Plaintext
115 lines
4.8 KiB
Plaintext
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The following instructions apply if you have a Linux or FreeBSD platform and
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want libpcap to support the DAG range of passive network monitoring cards from
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Endace (http://www.endace.com, see below for further contact details).
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1) Install and build the DAG software distribution by following the
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instructions supplied with that package. Current Endace customers can download
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the DAG software distibution from https://www.endace.com
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2) Configure libcap. To allow the 'configure' script to locate the DAG
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software distribution use the '--with-dag' option:
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./configure --with-dag=DIR
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Where DIR is the root of the DAG software distribution, for example
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/var/src/dag. If the DAG software is correctly detected 'configure' will
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report:
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checking whether we have DAG API... yes
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If 'configure' reports that there is no DAG API, the directory may have been
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incorrectly specified or the DAG software was not built before configuring
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libpcap.
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See also the libpcap INSTALL.txt file for further libpcap configuration
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options.
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Building libpcap at this stage will include support for both the native packet
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capture stream (linux or bpf) and for capturing from DAG cards. To build
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libpcap with only DAG support specify the capture type as 'dag' when
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configuring libpcap:
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./configure --with-dag=DIR --with-pcap=dag
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Applications built with libpcap configured in this way will only detect DAG
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cards and will not capture from the native OS packet stream.
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----------------------------------------------------------------------
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Libpcap when built for DAG cards against dag-2.5.1 or later releases:
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Timeouts are supported. pcap_dispatch() will return after to_ms milliseconds
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regardless of how many packets are received. If to_ms is zero pcap_dispatch()
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will block waiting for data indefinitely.
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pcap_dispatch() will block on and process a minimum of 64kB of data (before
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filtering) for efficiency. This can introduce high latencies on quiet
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interfaces unless a timeout value is set. The timeout expiring will override
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the 64kB minimum causing pcap_dispatch() to process any available data and
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return.
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pcap_setnonblock is supported. When nonblock is set, pcap_dispatch() will
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check once for available data, process any data available up to count, then
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return immediately.
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pcap_findalldevs() is supported, e.g. dag0, dag1...
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Some DAG cards can provide more than one 'stream' of received data.
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This can be data from different physical ports, or separated by filtering
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or load balancing mechanisms. Receive streams have even numbers, e.g.
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dag0:0, dag0:2 etc. Specifying transmit streams for capture is not supported.
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pcap_setfilter() is supported, BPF programs run in userspace.
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pcap_setdirection() is not supported. Only received traffic is captured.
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DAG cards normally do not have IP or link layer addresses assigned as
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they are used to passively monitor links.
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pcap_breakloop() is supported.
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pcap_datalink() and pcap_list_datalinks() are supported. The DAG card does
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not attempt to set the correct datalink type automatically where more than
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one type is possible.
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pcap_stats() is supported. ps_drop is the number of packets dropped due to
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RX stream buffer overflow, this count is before filters are applied (it will
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include packets that would have been dropped by the filter). The RX stream
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buffer size is user configurable outside libpcap, typically 16-512MB.
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pcap_get_selectable_fd() is not supported, as DAG cards do not support
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poll/select methods.
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pcap_inject() and pcap_sendpacket() are not supported.
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Some DAG cards now support capturing to multiple virtual interfaces, called
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streams. Capture streams have even numbers. These are available via libpcap
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as separate interfaces, e.g. dag0:0, dag0:2, dag0:4 etc. dag0:0 is the same
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as dag0. These are visible via pcap_findalldevs().
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libpcap now does NOT set the card's hardware snaplen (slen). This must now be
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set using the appropriate DAG coniguration program, e.g. dagthree, dagfour,
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dagsix, dagconfig. This is because the snaplen is currently shared between
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all of the streams. In future this may change if per-stream slen is
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implemented.
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DAG cards by default capture entire packets including the L2
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CRC/FCS. If the card is not configured to discard the CRC/FCS, this
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can confuse applications that use libpcap if they're not prepared for
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packets to have an FCS. Libpcap now reads the environment variable
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ERF_FCS_BITS to determine how many bits of CRC/FCS to strip from the
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end of the captured frame. This defaults to 32 for use with
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Ethernet. If the card is configured to strip the CRC/FCS, then set
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ERF_FCS_BITS=0. If used with a HDLC/PoS/PPP/Frame Relay link with 16
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bit CRC/FCS, then set ERF_FCS_BITS=16.
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----------------------------------------------------------------------
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Please submit bug reports via <support@endace.com>.
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Please also visit our Web site at:
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http://www.endace.com/
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For more information about Endace DAG cards contact <sales@endace.com>.
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