tcpdump.1

网卡驱动相关实例 这是和网卡NT KMD驱动程序有关的一些资料和例子。主要是以下三方面内容: 3.1 article 一些有用的文档 3.2 Canberra 网络诊听工具Ethern

On the 7th line, csam says it's received data sent by rtsg up to
but not including byte 21.  Most of this data is apparently sitting in the
socket buffer since csam's receive window has gotten 19 bytes smaller.
Csam also sends one byte of data to rtsg in this packet.
On the 8th and 9th lines,
csam sends two bytes of urgent, pushed data to rtsg.
.LP
If the snapshot was small enough that \fBtcpdump\fP didn't capture
the full TCP header, it interprets as much of the header as it can
and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
be interpreted.  If the header contains a bogus option (one with a length
that's either too small or beyond the end of the header), tcpdump reports
it as ``[\fIbad opt\fP]'' and does not interpret any further options (since
it's impossible to tell where they start).  If the header length indicates
options are present but the IP datagram length is not long enough for the
options to actually be there, tcpdump reports it as ``[\fIbad hdr length\fP]''.
.HD
.B
UDP Packets
.LP
UDP format is illustrated by this rwho packet:
.RS
.nf
.sp .5
\f(CWactinide.who > broadcast.who: udp 84\fP
.sp .5
.fi
.RE
This says that port \fIwho\fP on host \fIactinide\fP sent a udp
datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
broadcast address.  The packet contained 84 bytes of user data.
.LP
Some UDP services are recognized (from the source or destination
port number) and the higher level protocol information printed.
In particular, Domain Name service requests (RFC-1034/1035) and Sun
RPC calls (RFC-1050) to NFS.
.HD
UDP Name Server Requests
.LP
\fI(N.B.:The following description assumes familiarity with
the Domain Service protocol described in RFC-1035.  If you are not familiar
with the protocol, the following description will appear to be written
in greek.)\fP
.LP
Name server requests are formatted as
.RS
.nf
.sp .5
\fIsrc > dst: id op? flags qtype qclass name (len)\fP
.sp .5
\f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fP
.sp .5
.fi
.RE
Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
The query id was `3'.  The `+' indicates the \fIrecursion desired\fP flag
was set.  The query length was 37 bytes, not including the UDP and
IP protocol headers.  The query operation was the normal one, \fIQuery\fP,
so the op field was omitted.  If the op had been anything else, it would
have been printed between the `3' and the `+'.
Similarly, the qclass was the normal one,
\fIC_IN\fP, and omitted.  Any other qclass would have been printed
immediately after the `A'.
.LP
A few anomalies are checked and may result in extra fields enclosed in
square brackets:  If a query contains an answer, name server or
authority section,
.IR ancount ,
.IR nscount ,
or
.I arcount
are printed as `[\fIn\fPa]', `[\fIn\fPn]' or  `[\fIn\fPau]' where \fIn\fP
is the appropriate count.
If any of the response bits are set (AA, RA or rcode) or any of the
`must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
is printed, where \fIx\fP is the hex value of header bytes two and three.
.HD
UDP Name Server Responses
.LP
Name server responses are formatted as
.RS
.nf
.sp .5
\fIsrc > dst:  id op rcode flags a/n/au type class data (len)\fP
.sp .5
\f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fP
.sp .5
.fi
.RE
In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
with 3 answer records, 3 name server records and 7 authority records.
The first answer record is type A (address) and its data is internet
address 128.32.137.3.  The total size of the response was 273 bytes,
excluding UDP and IP headers.  The op (Query) and response code
(NoError) were omitted, as was the class (C_IN) of the A record.
.LP
In the second example, \fIhelios\fP responds to query 2 with a
response code of non-existent domain (NXDomain) with no answers,
one name server and no authority records.  The `*' indicates that
the \fIauthoritative answer\fP bit was set.  Since there were no
answers, no type, class or data were printed.
.LP
Other flag characters that might appear are `\-' (recursion available,
RA, \fInot\fP set) and `|' (truncated message, TC, set).  If the
`question' section doesn't contain exactly one entry, `[\fIn\fPq]'
is printed.
.LP
Note that name server requests and responses tend to be large and the
default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
to print.  Use the \fB\-s\fP flag to increase the snaplen if you
need to seriously investigate name server traffic.  `\fB\-s 128\fP'
has worked well for me.

.HD
NFS Requests and Replies
.LP
Sun NFS (Network File System) requests and replies are printed as:
.RS
.nf
.sp .5
\fIsrc.xid > dst.nfs: len op args\fP
\fIsrc.nfs > dst.xid: reply stat len op results\fP
.sp .5
\f(CW
sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
sushi.201b > wrl.nfs:
	144 lookup fh 9,74/4096.6878 "xcolors"
wrl.nfs > sushi.201b:
	reply ok 128 lookup fh 9,74/4134.3150
\fP
.sp .5
.fi
.RE
In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
to \fIwrl\fP (note that the number following the src host is a
transaction id, \fInot\fP the source port).  The request was 112 bytes,
excluding the UDP and IP headers.  The operation was a \fIreadlink\fP
(read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
(If one is lucky, as in this case, the file handle can be interpreted
as a major,minor device number pair, followed by the inode number and
generation number.)
\fIWrl\fP replies `ok' with the contents of the link.
.LP
In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
`\fIxcolors\fP' in directory file 9,74/4096.6878.  Note that the data printed
depends on the operation type.  The format is intended to be self
explanatory if read in conjunction with
an NFS protocol spec.
.LP
If the \-v (verbose) flag is given, additional information is printed.
For example:
.RS
.nf
.sp .5
\f(CW
sushi.1372a > wrl.nfs:
	148 read fh 21,11/12.195 8192 bytes @ 24576
wrl.nfs > sushi.1372a:
	reply ok 1472 read REG 100664 ids 417/0 sz 29388
\fP
.sp .5
.fi
.RE
(\-v also prints the IP header TTL, ID, and fragmentation fields,
which have been omitted from this example.)  In the first line,
\fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
at byte offset 24576.  \fIWrl\fP replies `ok'; the packet shown on the
second line is the first fragment of the reply, and hence is only 1472
bytes long (the other bytes will follow in subsequent fragments, but
these fragments do not have NFS or even UDP headers and so might not be
printed, depending on the filter expression used).  Because the \-v flag
is given, some of the file attributes (which are returned in addition
to the file data) are printed: the file type (``REG'', for regular file),
the file mode (in octal), the uid and gid, and the file size.
.LP
If the \-v flag is given more than once, even more details are printed.
.LP
Note that NFS requests are very large and much of the detail won't be printed
unless \fIsnaplen\fP is increased.  Try using `\fB\-s 192\fP' to watch
NFS traffic.
.LP
NFS reply packets do not explicitly identify the RPC operation.  Instead,
\fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
replies using the transaction ID.  If a reply does not closely follow the
corresponding request, it might not be parsable.
.HD
KIP Appletalk (DDP in UDP)
.LP
Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
and dumped as DDP packets (i.e., all the UDP header information is
discarded).  The file
.I /etc/atalk.names
is used to translate appletalk net and node numbers to names.
Lines in this file have the form
.RS
.nf
.sp .5
\fInumber	name\fP

\f(CW1.254		ether
16.1		icsd-net
1.254.110	ace\fP
.sp .5
.fi
.RE
The first two lines give the names of appletalk networks.  The third
line gives the name of a particular host (a host is distinguished
from a net by the 3rd octet in the number \-
a net number \fImust\fP have two octets and a host number \fImust\fP
have three octets.)  The number and name should be separated by
whitespace (blanks or tabs).
The
.I /etc/atalk.names
file may contain blank lines or comment lines (lines starting with
a `#').
.LP
Appletalk addresses are printed in the form
.RS
.nf
.sp .5
\fInet.host.port\fP

\f(CW144.1.209.2 > icsd-net.112.220
office.2 > icsd-net.112.220
jssmag.149.235 > icsd-net.2\fP
.sp .5
.fi
.RE
(If the
.I /etc/atalk.names
doesn't exist or doesn't contain an entry for some appletalk
host/net number, addresses are printed in numeric form.)
In the first example, NBP (DDP port 2) on net 144.1 node 209
is sending to whatever is listening on port 220 of net icsd node 112.
The second line is the same except the full name of the source node
is known (`office').  The third line is a send from port 235 on
net jssmag node 149 to broadcast on the icsd-net NBP port (note that
the broadcast address (255) is indicated by a net name with no host
number \- for this reason it's a good idea to keep node names and
net names distinct in /etc/atalk.names).
.LP
NBP (name binding protocol) and ATP (Appletalk transaction protocol)
packets have their contents interpreted.  Other protocols just dump
the protocol name (or number if no name is registered for the
protocol) and packet size.

\fBNBP packets\fP are formatted like the following examples:
.RS
.nf
.sp .5
\s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fP\s+2
.sp .5
.fi
.RE
The first line is a name lookup request for laserwriters sent by net icsd host
112 and broadcast on net jssmag.  The nbp id for the lookup is 190.
The second line shows a reply for this request (note that it has the
same id) from host jssmag.209 saying that it has a laserwriter
resource named "RM1140" registered on port 250.  The third line is
another reply to the same request saying host techpit has laserwriter
"techpit" registered on port 186.

\fBATP packet\fP formatting is demonstrated by the following example:
.RS
.nf
.sp .5
\s-2\f(CWjssmag.209.165 > helios.132: atp-req  12266<0-7> 0xae030001
helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
jssmag.209.165 > helios.132: atp-req  12266<3,5> 0xae030001
helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
jssmag.209.165 > helios.132: atp-rel  12266<0-7> 0xae030001
jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fP\s+2
.sp .5
.fi
.RE
Jssmag.209 initiates transaction id 12266 with host helios by requesting
up to 8 packets (the `<0-7>').  The hex number at the end of the line
is the value of the `userdata' field in the request.
.LP
Helios responds with 8 512-byte packets.  The `:digit' following the
transaction id gives the packet sequence number in the transaction
and the number in parens is the amount of data in the packet,
excluding the atp header.  The `*' on packet 7 indicates that the
EOM bit was set.
.LP
Jssmag.209 then requests that packets 3 & 5 be retransmitted.  Helios
resends them then jssmag.209 releases the transaction.  Finally,
jssmag.209 initiates the next request.  The `*' on the request
indicates that XO (`exactly once') was \fInot\fP set.

.HD
IP Fragmentation
.LP
Fragmented Internet datagrams are printed as
.RS
.nf
.sp .5
\fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
\fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
.sp .5
.fi
.RE
(The first form indicates there are more fragments.  The second
indicates this is the last fragment.)
.LP
\fIId\fP is the fragment id.  \fISize\fP is the fragment
size (in bytes) excluding the IP header.  \fIOffset\fP is this
fragment's offset (in bytes) in the original datagram.
.LP
The fragment information is output for each fragment.  The first
fragment contains the higher level protocol header and the frag
info is printed after the protocol info.  Fragments
after the first contain no higher level protocol header and the
frag info is printed after the source and destination addresses.
For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
over a CSNET connection that doesn't appear to handle 576 byte datagrams:
.RS
.nf
.sp .5
\s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
arizona > rtsg: (frag 595a:204@328)
rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
.sp .5
.fi
.RE
There are a couple of things to note here:  First, addresses in the
2nd line don't include port numbers.  This is because the TCP
protocol information is all in the first fragment and we have no idea
what the port or sequence numbers are when we print the later fragments.
Second, the tcp sequence information in the first line is printed as if there
were 308 bytes of user data when, in fact, there are 512 bytes (308 in
the first frag and 204 in the second).  If you are looking for holes
in the sequence space or trying to match up acks
with packets, this can fool you.
.LP
A packet with the IP \fIdon't fragment\fP flag is marked with a
trailing \fB(DF)\fP.
.HD
Timestamps
.LP
By default, all output lines are preceded by a timestamp.  The timestamp
is the current clock time in the form
.RS
.nf
\fIhh:mm:ss.frac\fP
.fi
.RE
and is as accurate as the kernel's clock.
The timestamp reflects the time the kernel first saw the packet.  No attempt
is made to account for the time lag between when the
ethernet interface removed the packet from the wire and when the kernel
serviced the `new packet' interrupt.
.SH "SEE ALSO"
traffic(1C), nit(4P), bpf(4), pcap(3)
.SH AUTHORS
Van Jacobson,
Craig Leres and
Steven McCanne, all of the
Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
.LP
The current version is available via anonymous ftp:
.LP
.RS
.I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
.RE
.SH BUGS
Please send bug reports to [e-mail].
.LP
NIT doesn't let you watch your own outbound traffic, BPF will.
We recommend that you use the latter.
.LP
Some attempt should be made to reassemble IP fragments or, at least
to compute the right length for the higher level protocol.
.LP
Name server inverse queries are not dumped correctly: The (empty)
question section is printed rather than real query in the answer
section.  Some believe that inverse queries are themselves a bug and
prefer to fix the program generating them rather than tcpdump.
.LP
Apple Ethertalk DDP packets could be dumped as easily as KIP DDP
packets but aren't.
Even if we were inclined to do anything to promote the use of
Ethertalk (we aren't), LBL doesn't allow Ethertalk on any of its
networks so we'd would have no way of testing this code.
.LP
A packet trace that crosses a daylight savings time change will give
skewed time stamps (the time change is ignored).
.LP
Filters expressions that manipulate FDDI headers assume that all FDDI
packets are encapsulated Ethernet packets.  This is true for IP, ARP,
and DECNET Phase IV, but is not true for protocols such as ISO CLNS.
Therefore, the filter may inadvertently accept certain packets that
do not properly match the filter expression.