tcpdump.1

Windump3.6.2源代码

By default a fairly minimal decode is done, with a much more detailed
decode done if -v is used. Be warned that with -v a single SMB packet
may take up a page or more, so only use -v if you really want all the
gory details.

If you are decoding SMB sessions containing unicode strings then you
may wish to set the environment variable USE_UNICODE to 1. A patch to
auto-detect unicode srings would be welcome.

For information on SMB packet formats and what all te fields mean see
www.cifs.org or the pub/samba/specs/ directory on your favourite
samba.org mirror site. The SMB patches were written by Andrew Tridgell
([e-mail]).

.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
\fR
.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, length, 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
AFS Requests and Replies
.LP
Transarc AFS (Andrew File System) requests and replies are printed
as:
.HD
.RS
.nf
.sp .5
\fIsrc.sport > dst.dport: rx packet-type\fP
\fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
\fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
.sp .5
\f(CW
elvis.7001 > pike.afsfs:
	rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
	new fid 536876964/1/1 ".newsrc"
pike.afsfs > elvis.7001: rx data fs reply rename
\fR
.sp .5
.fi
.RE
In the first line, host elvis sends a RX packet to pike.  This was
a RX data packet to the fs (fileserver) service, and is the start of
an RPC call.  The RPC call was a rename, with the old directory file id
of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
file id of 536876964/1/1 and a new filename of `.newsrc'.  The host pike
responds with a RPC reply to the rename call (which was successful, because
it was a data packet and not an abort packet).
.LP
In general, all AFS RPCs are decoded at least by RPC call name.  Most
AFS RPCs have at least some of the arguments decoded (generally only
the `interesting' arguments, for some definition of interesting).
.LP
The format is intended to be self-describing, but it will probably
not be useful to people who are not familiar with the workings of
AFS and RX.
.LP
If the -v (verbose) flag is given twice, acknowledgement packets and
additional header information is printed, such as the the RX call ID,
call number, sequence number, serial number, and the RX packet flags.
.LP
If the -v flag is given twice, additional information is printed,
such as the the RX call ID, serial number, and the RX packet flags.
The MTU negotiation information is also printed from RX ack packets.
.LP
If the -v flag is given three times, the security index and service id
are printed.
.LP
Error codes are printed for abort packets, with the exception of Ubik
beacon packets (because abort packets are used to signify a yes vote
for the Ubik protocol).
.LP
Note that AFS requests are very large and many of the arguments won't
be printed unless \fIsnaplen\fP is increased.  Try using `\fB-s 256\fP'
to watch AFS traffic.
.LP
AFS 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 call number and service 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\fR
.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\fR
.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\fR\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\fR\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
The original authors are:
.LP
Van Jacobson,
Craig Leres and
Steven McCanne, all of the
Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
.LP
It is currently being maintained by tcpdump.org.
.LP
The current version is available via http:
.LP
.RS
.I http://www.tcpdump.org/
.RE
.LP
The original distribution is available via anonymous ftp:
.LP
.RS
.I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
.RE
.LP
IPv6/IPsec support is added by WIDE/KAME project.
This program uses Eric Young's SSLeay library, under specific configuration.
.SH BUGS
Please send problems, bugs, questions, desirable enhancements, etc. to:
.LP
.RS
[e-mail]
.RE
.LP
Please send source code contributions, etc. to:
.LP
.RS
[e-mail]
.RE
.LP
NIT doesn't let you watch your own outbound traffic, BPF will.
We recommend that you use the latter.
.LP
On Linux systems with 2.0[.x] kernels:
.IP
packets on the loopback device will be seen twice;
.IP
packet filtering cannot be done in the kernel, so that all packets must
be copied from the kernel in order to be filtered in user mode;
.IP
all of a packet, not just the part that's within the snapshot length,
will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
asked to copy only part of a packet to userland, will not report the
true length of the packet; this would cause most IP packets to get an
error from
.BR tcpdump ).
.LP
We recommend that you upgrade to a 2.2 or later kernel.
.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 \fItcpdump\fP.
.LP
A packet trace that crosses a daylight savings time change will give
skewed time stamps (the time change is ignored).
.LP
Filter expressions that manipulate FDDI or Token Ring headers assume
that all FDDI and Token Ring packets are SNAP-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.
.LP
Filter expressions on fields other than those that manipulate Token Ring
headers will not correctly handle source-routed Token Ring packets.
.LP
.BR "ip6 proto"
should chase header chain, but at this moment it does not.
.BR "ip6 protochain"
is supplied for this behavior.
.LP
Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
does not work against IPv6 packets.
It only looks at IPv4 packets.