The following instructions apply if you have a Linux or FreeBSD platform and

want libpcap to support the DAG range of passive network monitoring cards from

Endace (http://www.endace.com, see below for further contact details).

1) Install and build the DAG software distribution by following the

instructions supplied with that package. Current Endace customers can download

the DAG software distribution from https://www.endace.com

2) Configure libcap. To allow the 'configure' script to locate the DAG

software distribution use the '--with-dag' option:

        ./configure --with-dag=DIR

Where DIR is the root of the DAG software distribution, for example

/var/src/dag. If the DAG software is correctly detected 'configure' will

report:

        checking whether we have DAG API... yes

If 'configure' reports that there is no DAG API, the directory may have been

incorrectly specified or the DAG software was not built before configuring

libpcap.

See also the libpcap INSTALL.txt file for further libpcap configuration

options.

Building libpcap at this stage will include support for both the native packet

capture stream (linux or bpf) and for capturing from DAG cards. To build

libpcap with only DAG support specify the capture type as 'dag' when

configuring libpcap:

        ./configure --with-dag=DIR --with-pcap=dag

Applications built with libpcap configured in this way will only detect DAG

cards and will not capture from the native OS packet stream.

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Libpcap when built for DAG cards against dag-2.5.1 or later releases:

Timeouts are supported. pcap_dispatch() will return after to_ms milliseconds

regardless of how many packets are received. If to_ms is zero pcap_dispatch()

will block waiting for data indefinitely.

pcap_dispatch() will block on and process a minimum of 64kB of data (before

filtering) for efficiency. This can introduce high latencies on quiet

interfaces unless a timeout value is set. The timeout expiring will override

the 64kB minimum causing pcap_dispatch() to process any available data and

return.

pcap_setnonblock is supported. When nonblock is set, pcap_dispatch() will

check once for available data, process any data available up to count, then

return immediately.

pcap_findalldevs() is supported, e.g. dag0, dag1...

Some DAG cards can provide more than one 'stream' of received data.

This can be data from different physical ports, or separated by filtering

or load balancing mechanisms. Receive streams have even numbers, e.g.

dag0:0, dag0:2 etc. Specifying transmit streams for capture is not supported.

pcap_setfilter() is supported, BPF programs run in userspace.

pcap_setdirection() is not supported. Only received traffic is captured.

DAG cards normally do not have IP or link layer addresses assigned as

they are used to passively monitor links.

pcap_breakloop() is supported.

pcap_datalink() and pcap_list_datalinks() are supported. The DAG card does

not attempt to set the correct datalink type automatically where more than

one type is possible.

pcap_stats() is supported. ps_drop is the number of packets dropped due to

RX stream buffer overflow, this count is before filters are applied (it will

include packets that would have been dropped by the filter). The RX stream

buffer size is user configurable outside libpcap, typically 16-512MB.

pcap_get_selectable_fd() is not supported, as DAG cards do not support

poll/select methods.

pcap_inject() and pcap_sendpacket() are not supported.

Some DAG cards now support capturing to multiple virtual interfaces, called

streams. Capture streams have even numbers. These are available via libpcap

as separate interfaces, e.g. dag0:0, dag0:2, dag0:4 etc. dag0:0 is the same

as dag0. These are visible via pcap_findalldevs().

libpcap now does NOT set the card's hardware snaplen (slen). This must now be

set using the appropriate DAG configuration program, e.g. dagthree, dagfour,

dagsix, dagconfig. This is because the snaplen is currently shared between

all of the streams. In future this may change if per-stream slen is

implemented.

DAG cards by default capture entire packets including the L2

CRC/FCS. If the card is not configured to discard the CRC/FCS, this

can confuse applications that use libpcap if they're not prepared for

packets to have an FCS.

Libpcap now reads the environment variable ERF_FCS_BITS to determine

how many bits of CRC/FCS to strip from the end of the captured

frame. This defaults to 32 for use with Ethernet. If the card is

configured to strip the CRC/FCS, then set ERF_FCS_BITS=0. If used with

a HDLC/PoS/PPP/Frame Relay link with 16 bit CRC/FCS, then set

ERF_FCS_BITS=16.

If you wish to create a pcap file that DOES contain the Ethernet FCS,

specify the environment variable ERF_DONT_STRIP_FCS. This will cause

the existing FCS to be captured into the pcap file. Note some

applications may incorrectly report capture errors or oversize packets

when reading these files.

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Please submit bug reports via <support@endace.com>.

Please also visit our Web site at:

        http://www.endace.com/

For more information about Endace DAG cards contact <sales@endace.com>.