tcpdump.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

19 bytes of data (bytes 2 through 20
in the rtsg \(-> csam side of the conversation).
The PUSH flag is set in the packet.
On the 7th line, 
.PN csam 
says it has received data sent by 
.PN rtsg 
up to
but not including byte 21.  Most of this data is apparently sitting in the
socket buffer since 
.PN csam 's 
receive window has gotten 19 bytes smaller.
.PN Csam 
also sends one byte of data to 
.PN rtsg 
in this packet.
On the 8th and 9th lines,
.PN csam 
sends two bytes of urgent, pushed data to 
.PN rtsg .
.sp
.sp
.B "UDP Packets"
.PP
UDP format is illustrated by this 
.PN rwho 
packet:
.EX
\f(CWactinide.who > broadcast.who: udp 84\fP
.EE
This says that port \fIwho\fP on host 
.PN actinide
sent a udp
datagram to port \fIwho\fP on host 
.PN broadcast , 
the Internet
broadcast address.  The packet contained 84 bytes of user data.
.PP
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.
.sp
.sp
.B "UDP Name Server Requests"
.PP
.NT
The following description assumes familiarity with
the Domain Service protocol described in RFC-1035.  
.NE
.PP
Name server requests are formatted as follows:
.EX
\fIsrc > dst: id op? flags qtype qclass name (len)\fP
.sp
\f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fP
.EE
Host 
.PN h2opolo
asked the domain server on 
.PN helios
for an
address record (qtype=A) associated with the name 
.PN ucbvax.berkeley.edu .
The query id is `3'.  The `+' indicates the \fIrecursion desired\fP flag
was set.  The query length is 37 bytes, not including the UDP and
IP protocol headers.  The query operation is the normal one, \fIQuery\fP,
so the \fIop\fP field was omitted.  If the \fIop\fP had been 
anything else, it would be printed between the `3' and the `+'.
Similarly, the \fIqclass\fP is the normal one,
\fIC_IN\fP, and omitted.  Any other \fPqclass\fP would be printed
immediately after the `A'.
.PP
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.
.sp
.sp
.B "UDP Name Server Responses"
.PP
Name server responses are formatted as follows:
.EX
\fIsrc > dst:  id op rcode flags a/n/au type class data (len)\fP
.sp
\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
.EE
In the first example, 
.PN helios
responds to query id 3 from 
.PN h2opolo
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 \fIop\fP (Query) and response code
(NoError) were omitted, as was the \fIclass\fP (C_IN) of the A record.
.PP
In the second example, 
.PN helios
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.
.PP
Other flag characters that might appear are `\-' (recursion available,
RA, \fInot\fP set) and `|' (truncated message, TC, set).  If the
`question' section does not contain exactly one entry, `[\fIn\fPq]'
is printed.
.PP
Note that name server requests and responses tend to be large and the
default \fIsnaplen\fP of 96 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.  For example, 
`\fB\-s 128\fP' works well.
.sp
.sp
.B "NFS Requests"
.PP
Sun NFS (Network File System) requests and replies are printed as:
.EX
\fIsrc.xid > dst.nfs: len op args\fP
\fIsrc.nfs > dst.xid: reply stat len\fP
.sp
\f(CWvs.e2766 > helios.nfs: 136 readdir fh 6.5197 8192 bytes @ 0
helios.nfs > vs.e2766: reply ok 384
vs.e2767 > helios.nfs: 136 lookup fh 6.5197 `RCS'\fP
.EE
In the first line, host 
.PN vs
sends a transaction with id \fIe2766\fP
to 
.PN helios 
(note that the number following the src host is a
transaction id, \fInot\fP the source port).  The request was 136 bytes,
excluding the UDP and IP headers.  The operation was a \fIreaddir\fP
(read directory) on file handle (\fIfh\fP) 6.5197.  8192 bytes are
read, starting at offset 0.  
.PN Helios
replies `ok' with 384
bytes of data.  (The design of Sun's RPC protocol makes it difficult to
interpret replies.)
.PP
In the third line, 
.PN vs 
asks 
.PN helios
to lookup the name
`\fIRCS\fP' in directory file 6.5197.  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.
.PP
Note that NFS requests are very large and the above will not be printed
unless \fIsnaplen\fP is increased.  You can use `\fB\-s 192\fP' to watch
NFS traffic.
.sp
.sp
.B "KIP Appletalk (DDP in UDP)"
.PP
Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
and dumped as DDP packets (that is, all the UDP header information is
discarded).  The file
.PN /etc/atalk.names
file is used to translate appletalk net and node numbers to names.
Lines in this file have the form
.EX
\fInumber          name\fP
.sp
\f(CW1.254           ether
16.1            icsd-net
1.254.110       ace\fP
.EE
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
.PN /etc/atalk.names
file may contain blank lines or comment lines (lines starting with
a `#').
.PP
Appletalk addresses are printed in the form
.EX
\fInet.host.port\fP
.sp
\f(CW144.1.209.2 > icsd-net.112.220
office.2 > icsd-net.112.220
jssmag.149.235 > icsd-net.2\fP
.EE
(If the
.PN /etc/atalk.names
file does not exist or does not 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 is a good idea to keep node names and
net names distinct in the
.PN /etc/atalk.names 
file).
.PP
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.
.PP
\fBNBP packets\fP are formatted like the following examples:
.EX
\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
.EE
The first line is a name lookup request for laserwriters sent by net 
.PN icsd 
host
.PN 112 
and broadcast on net 
.PN 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 
.PN 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 
.PN techpit 
has laserwriter
"techpit" registered on port 186.
.PP
\fBATP packet\fP formatting is demonstrated by the following example:
.EX
\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
.EE
.PN Jssmag.209 
initiates transaction id 12266 with host 
.PN 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.
.PP
.PN 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.
.PP
.PN Jssmag.209 
then requests that packets 3 & 5 be retransmitted.  
.PN Helios
resends them and then 
.PN jssmag.209 
releases the transaction.  Finally,
.PN jssmag.209 
initiates the next request.  The `*' on the request
indicates that XO (`exactly once') was \fInot\fP set.
.sp
.sp
.B "IP Fragmentation"
.PP
Fragmented Internet datagrams are printed as
.EX
\fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
\fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
.EE
(The first form indicates there are more fragments.  The second
indicates this is the last fragment.)
.PP
\fIId\fP is the fragment id (in hex).  \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.
.PP
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 
.PN arizona.edu 
to 
.PN lbl-rtsg.arpa
over a CSNET connection that does not appear to handle 576 byte datagrams:
.EX
\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
.EE
There are a couple of things to note here:  First, addresses in the
2nd line do not 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.
.PP
A packet with the IP \fIdon't fragment\fP flag is marked with a
trailing \fB(DF)\fP.
.sp
.sp
.B "Timestamps"
.PP
By default, all output lines are preceded by a timestamp.  The timestamp
is the current clock time in the form
.EX
\fIhh:mm:ss.frac\fP
.EE
and is as accurate as the kernel's clock (for example, \(+-4ms on an
ULTRIX RISC workstation).
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 Copyright
Copyright (c) 1988-1990 The Regents of the University of California.
All rights reserved.
.PP
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that: (1) source code distributions
retain the above copyright notice and this paragraph in its entirety, (2)
distributions including binary code include the above copyright notice and
this paragraph in its entirety in the documentation or other materials
provided with the distribution, and (3) all advertising materials mentioning
features or use of this software display the following acknowledgement:
``This product includes software developed by the University of California,
Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
the University nor the names of its contributors may be used to endorse
or promote products derived from this software without specific prior
written permission.
THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.SH See Also
packetfilter(4), pfconfig(8c), pfstat(8)