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2 The following instructions apply if you have a Linux or FreeBSD platform and
3 want libpcap to support the DAG range of passive network monitoring cards from
4 Endace (http://www.endace.com, see below for further contact details).
5  
6 1) Install and build the DAG software distribution by following the
7 instructions supplied with that package. Current Endace customers can download
8 the DAG software distibution from https://www.endace.com
9  
10 2) Configure libcap. To allow the 'configure' script to locate the DAG
11 software distribution use the '--with-dag' option:
12  
13 ./configure --with-dag=DIR
14  
15 Where DIR is the root of the DAG software distribution, for example
16 /var/src/dag. If the DAG software is correctly detected 'configure' will
17 report:
18  
19 checking whether we have DAG API... yes
20  
21 If 'configure' reports that there is no DAG API, the directory may have been
22 incorrectly specified or the DAG software was not built before configuring
23 libpcap.
24  
25 See also the libpcap INSTALL.txt file for further libpcap configuration
26 options.
27  
28 Building libpcap at this stage will include support for both the native packet
29 capture stream (linux or bpf) and for capturing from DAG cards. To build
30 libpcap with only DAG support specify the capture type as 'dag' when
31 configuring libpcap:
32  
33 ./configure --with-dag=DIR --with-pcap=dag
34  
35 Applications built with libpcap configured in this way will only detect DAG
36 cards and will not capture from the native OS packet stream.
37  
38 ----------------------------------------------------------------------
39  
40 Libpcap when built for DAG cards against dag-2.5.1 or later releases:
41  
42 Timeouts are supported. pcap_dispatch() will return after to_ms milliseconds
43 regardless of how many packets are received. If to_ms is zero pcap_dispatch()
44 will block waiting for data indefinitely.
45  
46 pcap_dispatch() will block on and process a minimum of 64kB of data (before
47 filtering) for efficiency. This can introduce high latencies on quiet
48 interfaces unless a timeout value is set. The timeout expiring will override
49 the 64kB minimum causing pcap_dispatch() to process any available data and
50 return.
51  
52 pcap_setnonblock is supported. When nonblock is set, pcap_dispatch() will
53 check once for available data, process any data available up to count, then
54 return immediately.
55  
56 pcap_findalldevs() is supported, e.g. dag0, dag1...
57  
58 Some DAG cards can provide more than one 'stream' of received data.
59 This can be data from different physical ports, or separated by filtering
60 or load balancing mechanisms. Receive streams have even numbers, e.g.
61 dag0:0, dag0:2 etc. Specifying transmit streams for capture is not supported.
62  
63 pcap_setfilter() is supported, BPF programs run in userspace.
64  
65 pcap_setdirection() is not supported. Only received traffic is captured.
66 DAG cards normally do not have IP or link layer addresses assigned as
67 they are used to passively monitor links.
68  
69 pcap_breakloop() is supported.
70  
71 pcap_datalink() and pcap_list_datalinks() are supported. The DAG card does
72 not attempt to set the correct datalink type automatically where more than
73 one type is possible.
74  
75 pcap_stats() is supported. ps_drop is the number of packets dropped due to
76 RX stream buffer overflow, this count is before filters are applied (it will
77 include packets that would have been dropped by the filter). The RX stream
78 buffer size is user configurable outside libpcap, typically 16-512MB.
79  
80 pcap_get_selectable_fd() is not supported, as DAG cards do not support
81 poll/select methods.
82  
83 pcap_inject() and pcap_sendpacket() are not supported.
84  
85 Some DAG cards now support capturing to multiple virtual interfaces, called
86 streams. Capture streams have even numbers. These are available via libpcap
87 as separate interfaces, e.g. dag0:0, dag0:2, dag0:4 etc. dag0:0 is the same
88 as dag0. These are visible via pcap_findalldevs().
89  
90 libpcap now does NOT set the card's hardware snaplen (slen). This must now be
91 set using the appropriate DAG coniguration program, e.g. dagthree, dagfour,
92 dagsix, dagconfig. This is because the snaplen is currently shared between
93 all of the streams. In future this may change if per-stream slen is
94 implemented.
95  
96 DAG cards by default capture entire packets including the L2
97 CRC/FCS. If the card is not configured to discard the CRC/FCS, this
98 can confuse applications that use libpcap if they're not prepared for
99 packets to have an FCS.
100  
101 Libpcap now reads the environment variable ERF_FCS_BITS to determine
102 how many bits of CRC/FCS to strip from the end of the captured
103 frame. This defaults to 32 for use with Ethernet. If the card is
104 configured to strip the CRC/FCS, then set ERF_FCS_BITS=0. If used with
105 a HDLC/PoS/PPP/Frame Relay link with 16 bit CRC/FCS, then set
106 ERF_FCS_BITS=16.
107  
108 If you wish to create a pcap file that DOES contain the Ethernet FCS,
109 specify the environment variable ERF_DONT_STRIP_FCS. This will cause
110 the existing FCS to be captured into the pcap file. Note some
111 applications may incorrectly report capture errors or oversize packets
112 when reading these files.
113  
114 ----------------------------------------------------------------------
115  
116 Please submit bug reports via <support@endace.com>.
117  
118 Please also visit our Web site at:
119  
120 http://www.endace.com/
121  
122 For more information about Endace DAG cards contact <sales@endace.com>.