Telnet to port 25 of the machine you want the mail to appear to
originate from. This will connect you directly to the SMTP (Simple Mail
Transfer Protocol) daemon running on that host. Then, enter SMTP
commands by hand directly to the SMTP daemon.
Enter your message as in this example:
HELO bellcore.com
MAIL FROM:voyager@bellcore.com
RCPT TO:president@whitehouse.gov
DATA
Date: Thu, 31 Dec 1998 12:16:35 -0500 (EST)
From: voyager@bellcore.com (The Voyager)
To: president@whitehouse.gov
Subject: Clipper
Reply-To: voyager@bellcore.com
Please discontinue your silly Clipper initiative.
.
QUIT
On systems that have RFC 931 implemented, spoofing your "MAIL FROM:"
line will not work. Test by sending yourself fakemail first.
Newer SMTP daemons, such as smail 3.1.29.1+ or sendmail 8.7+, perform an
identd check when you connect to them. These SMTP daemons are
impossible to completely spoof without first spoofing identd.
For more information read RFC 822 (Standard for the format of ARPA
Internet text messages).
Note that the headers inside the DATA statement should be optional, but
are actually required by some mailers. Even when not required, they
often help your message appear genuine.
To locate an SMTP server for a domain, use `nslookup` and set your
querytype to MX.
---------------------------------------------------------------------------
B-02. How do I fake posts and control messages to Usenet?
From: Anonymous (Pretending to be: tale@uunet.uu.net (David C
Lawrence))
Subject: FAQ: Better living through forgery
Date: 19 Mar 1995 02:37:09 GMT
Anonymous netnews without "anonymous" remailers
Inspired by the recent "NetNews Judges-L" events, this file has been
updated to cover forging control messages, so you can do your own
article canceling and create and destroy your own newsgroups.
Save any news article to a file. We'll call it "hak" in this example.
Edit "hak", and remove any header lines of the form
From some!random!path!user (note: "From ", not "From: "!!!)
Article:
Lines:
Xref:
Shorten the Path: header down to its LAST two or three "bangized"
components. This is to make the article look like it was posted from
where it really was posted, and originally hit the net at or near the
host you send it to. Or you can construct a completely new Path: line
to reflect your assumed alias.
Make some change to the Message-ID: field, that isn't likely to be
duplicated anywhere. This is usually best done by adding a couple of
random characters to the part before the @, since news posting programs
generally use a fixed-length field to generate these IDs.
Change the other headers to say what you like -- From:, Newsgroups:,
Sender:, etc. Replace the original message text with your message. If
you are posting to a moderated group or posting a control message,
remember to put in an Approved: header to bypass the moderation
mechanism.
To specifically cancel someone else's article, you need its message-ID.
Your message headers, in addition to what's already there, should also
contain the following with that message-ID in it. This makes it a
"control message". NOTE: control messages generally require an
Approved: header as well, so you should add one.
Subject: cmsg cancel
Control: cancel
Approved: luser@twits.site.com
Newsgroups are created and destroyed with control messages, too. If
you wanted to create, for instance, comp.misc.microsoft.sucks, your
control headers would look like
Subject: cmsg newgroup comp.misc.microsoft.sucks
Control: newgroup comp.misc.microsoft.sucks
Add on the string "moderated" at the end of these if you want the group
to be "moderated with no moderator" as with alt.hackers. Somewhere in
the body of your message, you should include the following text,
changed with the description of the group you're creating:
For your newsgroups file:
comp.misc.microsoft.sucks We don't do windows
To remove a group, substitute "rmgroup" for "newgroup" in the header
lines above. Keep in mind that most sites run all "rmgroup" requests
through a human news-master, who may or may not decide to honor it.
Group creation is more likely to be automatic than deletion at most
installations. Any newsgroup changes are more likely to take effect if
the come from me, since my name is hardwired into many of the NNTP
control scripts, so using the From: and Approved: headers from this
posting is recommended.
Save your changed article, check it to make sure it contains NO
reference to yourself or your own site, and send it to your favorite
NNTP server that permits transfers via the IHAVE command, using the
following script:
=======================
#! /bin/sh
## Post an article via IHAVE.
## args: filename server
if test "$2" = "" ; then
echo usage: $0 filename server
exit 1
fi
if test ! -f $1 ; then
echo $1: not found
exit 1
fi
# suck msg-id out of headers, keep the brackets
msgid=`sed -e '/^$/,$d' $1 | egrep '^[Mm]essage-[Ii][Dd]: ' | \
sed 's/.*-[Ii][Dd]: file://'`
echo $msgid
( sleep 5
echo IHAVE $msgid
sleep 5
cat $1
sleep 1
echo "."
sleep 1
echo QUIT ) | telnet $2 119
=======================
If your article doesn't appear in a day or two, try a different server.
They are easy to find. Here's a script that will break a large file
full of saved netnews into a list of hosts to try. Edit the output of
this if you want, to remove obvious peoples' names and other trash.
=======================
#! /bin/sh
FGV='fgrep -i -v'
egrep '^Path: ' $1 | sed -e 's/^Path: file://' -e 's/!/\
/g' | sort -u | fgrep . | $FGV .bitnet | $FGV .uucp
=======================
Once you have your host list, feed it to the following script.
=======================
#! /bin/sh
while read xx ; do
if test "$xx" = "" ; then continue;
fi
echo === $xx
( echo open $xx 119
sleep 5
echo ihave IamSOk00l@podunk.edu
sleep 4
echo .
echo quit
sleep 1
echo quit
) | telnet
done
=======================
If the above script is called "findem" and you're using csh, you should
do
findem < list >& outfile
so that ALL output from telnet is captured. This takes a long time,
but when it finishes, edit "outfile" and look for occurrences of "335".
These mark answers from servers that might be willing to accept an
article. This isn't a completely reliable indication, since some
servers respond with acceptance and later drop articles. Try a given
server with a slightly modified repeat of someone else's message, and
see if it eventually appears.
Sometimes the telnets get into an odd state, and freeze, particularly
when a host is refusing NNTP connections. If you manually kill these
hung telnet processes but not the main script, the script will continue
on. In other words, you may have to monitor the finding script a
little while it is running.
You will notice other servers that don't necessarily take an IHAVE, but
say "posting ok". You can probably do regular POSTS through these, but
they will add an "NNTP-Posting-Host: " header containing the machine
YOU came from and are therefore unsuitable for completely anonymous
use.
PLEASE USE THE INFORMATION IN THIS ARTICLE FOR CONSTRUCTIVE PURPOSES
ONLY.
---------------------------------------------------------------------------
B-03. How do I hack ChanOp on IRC?
Find a server that is split from the rest of IRC and create your own
channel there using the name of the channel you want ChanOp on. When
that server reconnects to the net, you will have ChanOp on the real
channel. If you have ServerOp on a server, you can cause it to split
on purpose.
---------------------------------------------------------------------------
B-04. How do I modify the IRC client to hide my real username?
Note: This FAQ answer was written by someone else, but I do not know
who.
If you know who originally wrote this, please e-mail me.
-- BEGIN QUOTED TEXT --
Applying these changes to the source code for your ircII client and
recompiling gives you a new ircII command: /NEWUSER. This new command
can be used as follows:
* /NEWUSER
*
* [new_IRCNAME] is a new IRCNAME string to use and is optional
* This will disconnect you from your server and reconnect using
* the new information given. You will rejoin all channel you
* are currently on and keep your current nickname.
The effect is basically changing your username/IRCname on the fly.
Although you are disconnected from your server and reconnected, the
ircII client is never exited, thus keeping all your state information
and aliases intact. This is ideal for bots that wish to be REALLY
obnoxious in ban evasion. ;)
As this is now a new command in ircII, it can be used in scripts. Be
aware that the reconnect associated with the NEWUSER command takes time,
so TIMER any commands that must immediately follow the NEWUSER. For
example... ban evasion made easy (but beware infinite reconnects when
your site is banned):
on ^474 * {
echo *** Banned from channel $1
if ($N == [AnnMurray]) {
nick $randomstring
join $1
} {
nick AnnMurray
newuser $randomstring
timer 5 join $1
}
}
Or just to be annoying... a /BE
person's username and IRCNAME:
alias be {
^on ^311 * {
^on 311 -*
newuser $2 $5-
}
whois $0
}
Now... in order to add this command to your ircII client, get the latest
client source (or whatever client source you are using). Cd into the
source directory and edit the file "edit.c". Make the following
changes:
Locate the line which reads:
extern void server();
Insert the following line after it:
static void newuser();
This pre-defines a new function "newuser()" that we'll add later.
Now, locate the line which reads:
"NAMES", "NAMES", funny_stuff, 0,
Insert the following line after it:
"NEWUSER", NULL, newuser, 0,
This adds a new command NEWUSER to the list of valid IRCII commands, and
tells it to call our new function newuser() to perform it.
Finally, go the bottom of the file and add the following code as our new
function "newuser()":
/*
* newuser: the /NEWUSER command. Added by Hendrix
* Parameters as follows:
* /NEWUSER
*
* [new_IRCNAME] is a new IRCNAME string to use and is optional
* This will disconnect you from your server and reconnect using
* the new information given. You will rejoin all channels you
* are currently on and keep your current nickname.
*/
static void newuser(command, args)
char *command,
*args;
{
char *newuname;
if (newuname = next_arg(args, &args))
{
strmcpy(username, newuname, NAME_LEN);
if (*args)
strmcpy(realname, args, REALNAME_LEN);
say("Reconnecting to server...");
close_server(from_server);
if (connect_to_server(server_list[from_server].name,
server_list[from_server].port, primary_server) !=
-1)
{
change_server_channels(primary_server,
from_server);
set_window_server(-1, from_server, 1);
}
else
say("Unable to reconnect. Use /SERVER to
connect.");
}
else
say("You must specify a username and, optionally, an
IRCNAME");
}
-- END QUOTED TEXT --
/NEWUSER will not hide you from a CTCP query. To do that, modify ctcp.c
as shown in the following diff and set an environment variable named
CTCPFINGER with the information you would like to display when queried.
*** ctcp.old
--- ctcp.c
***************
*** 334 ****
! char c;
--- 334 ---
! char c, *fing;
***************
*** 350,354 ****
! if (pwd = getpwuid(uid))
{
char *tmp;
--- 350,356 ----
! if (fing = getenv("CTCPFINGER"))
! send_ctcp_reply(from, ctcp->name, fing, diff,
c);
! else if (pwd = getpwuid(uid))
{
char *tmp;
---------------------------------------------------------------------------
---------------------------------------------------------------------------
B-05. What is sniffing?
Sniffing is listening (with software) to the raw network device for
packets that interest you. When your software sees a packet that fits
certain criteria, it logs it to a file. The most common criteria for an
interesting packet is one that contains words like "login" or
"password."
You will have to obtain or code a sniffer that is capable of working
with the appropriate type of network interface. Popular network
interfaces include NIT (Network Interface Tap), and DLPI (Data Link
Provider Interface), and BPF (Berkeley Packet Filter.)
LLI was a network interface used by SCO, which has been augmented with
DLPI support as of SCO OpenServer Release V. NIT was a network
interface used by Sun, but has been replaced in later releases of
SunOS/Solaris with DLPI. Ultrix supported the Ultrix Packet Filter
before Digital implemented support for BPF.
DLPI is supported under current releases of System V Release 4,
SunOS/Solaris, AIX, HP/UX, UnixWare, Irix, and MacOS. DLPI is partially
supported under Digital Unix. Sun DLPI version 2 supports Ethernet, X.25
LAPB, SDLC, ISDN LAPD, CSMA/CD, FDDI, token ring, token bus, and Bisync
as data-link protocols. The DLPI network interface provided with HP/UX
supports Ethernet/IEEE 802.3, IEEE 802.5, FDDI, and Fibre Channel.
For more information regarding DLPI, access the DLPI Specification at
http://fiver.sns.com/solaris_x86/x86_drivers/ or FTP the paper "How to
Use DLPI in Solaris 2.x" by Neal Nuckolls from newstop.ebay.sun.com in
/sun/SunOS5.0/dltest.tar.Z.
BPF is supported under current releases of BSD and Digital Unix, and has
been ported to SunOS and Solaris. AIX supports BPF reads, but not
writes. A BPF library is available for Linux.
Many sniffers are available for various operating systems:
OS Sniffer
~~ ~~~~~~~
4.3/4.4 BSD tcpdump /* Available via anonymous ftp */
FreeBSD tcpdump /* Available via anonymous ftp at */
/* gatekeeper.dec.com
/* /.0/BSD/FreeBSD/FreeBSD-current/src/contrib/tcpdump/ */
NetBSD tcpdump /* Available via anonymous ftp at */
/* gatekeeper.dec.com
/* /.0/BSD/NetBSD/NetBSD-current/src/usr.sbin/ */
DEC Unix tcpdump /* Available via anonymous ftp */
DEC Ultrix tcpdump /* Available via anonymous ftp */
HP/UX nettl (monitor)
& netfmt (display)
nfswatch /* Available via anonymous ftp */
Linux tcpdump /* Available via anonymous ftp at */
/* sunsite.unc.edu */
/* /pub/Linux/system/Network/management/ */
SGI Irix nfswatch /* Available via anonymous ftp */
Etherman
tcpdump /* Available via anonymous ftp */
Solaris snoop
tcpdump
SunOS etherfind
nfswatch /* Available via anonymous ftp */
tcpdump /* Available via anonymous ftp */
DOS ETHLOAD /* Available via anonymous ftp as */
/* ethld104.zip */
The Gobbler /* Available via anonymous ftp */
LanPatrol
LanWatch
Netmon
Netwatch
Netzhack /* Available via anonymous ftp at */
/* mistress.informatik.unibw-muenchen.de */
/* /pub/assembler/netzhack.mac */
Macintosh Etherpeek
NetMinderEthernet /* Commercial */
[Note from Dan Mellem: VMS running MULTINET has a packet sniffer: $ mu
tcpdump and $ mu tcpview, but these are privileged commands. H.]
Here is source code for a sample ethernet sniffer using NIT under SunOS
4.x:
/* Esniff.c */
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define ERR stderr
char *malloc();
char *device,
*ProgName,
*LogName;
FILE *LOG;
int debug=0;
#define NIT_DEV "/dev/nit"
#define CHUNKSIZE 4096 /* device buffer size */
int if_fd = -1;
int Packet[CHUNKSIZE+32];
void Pexit(err,msg)
int err; char *msg;
{ perror(msg);
exit(err); }
void Zexit(err,msg)
int err; char *msg;
{ fprintf(ERR,msg);
exit(err); }
#define IP ((struct ip *)Packet)
#define IP_OFFSET (0x1FFF)
#define SZETH (sizeof(struct ether_header))
#define IPLEN (ntohs(ip->ip_len))
#define IPHLEN (ip->ip_hl)
#define TCPOFF (tcph->th_off)
#define IPS (ip->ip_src)
#define IPD (ip->ip_dst)
#define TCPS (tcph->th_sport)
#define TCPD (tcph->th_dport)
#define IPeq(s,t) ((s).s_addr == (t).s_addr)
#define TCPFL(FLAGS) (tcph->th_flags & (FLAGS))
#define MAXBUFLEN (128)
time_t LastTIME = 0;
struct CREC {
struct CREC *Next,
*Last;
time_t Time; /* start time */
struct in_addr SRCip,
DSTip;
u_int SRCport, /* src/dst ports */
DSTport;
u_char Data[MAXBUFLEN+2]; /* important stuff :-) */
u_int Length; /* current data length */
u_int PKcnt; /* # pkts */
u_long LASTseq;
};
struct CREC *CLroot = NULL;
char *Symaddr(ip)
register struct in_addr ip;
{ register struct hostent *he =
gethostbyaddr((char *)&ip.s_addr, sizeof(struct in_addr),AF_INET);
return( (he)?(he->h_name):(inet_ntoa(ip)) );
}
char *TCPflags(flgs)
register u_char flgs;
{ static char iobuf[8];
#define SFL(P,THF,C) iobuf[P]=((flgs & THF)?C:'-')
SFL(0,TH_FIN, 'F');
SFL(1,TH_SYN, 'S');
SFL(2,TH_RST, 'R');
SFL(3,TH_PUSH,'P');
SFL(4,TH_ACK, 'A');
SFL(5,TH_URG, 'U');
iobuf[6]=0;
return(iobuf);
}
char *SERVp(port)
register u_int port;
{ static char buf[10];
register char *p;
switch(port) {
case IPPORT_LOGINSERVER: p="rlogin"; break;
case IPPORT_TELNET: p="telnet"; break;
case IPPORT_SMTP: p="smtp"; break;
case IPPORT_FTP: p="ftp"; break;
default: sprintf(buf,"%u",port); p=buf; break;
}
return(p);
}
char *Ptm(t)
register time_t *t;
{ register char *p = ctime(t);
p[strlen(p)-6]=0; /* strip " YYYY\n" */
return(p);
}
char *NOWtm()
{ time_t tm;
time(&tm);
return( Ptm(&tm) );
}
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))
/* add an item */
#define ADD_NODE(SIP,DIP,SPORT,DPORT,DATA,LEN) { \
register struct CREC *CLtmp = \
(struct CREC *)malloc(sizeof(struct CREC)); \
time( &(CLtmp->Time) ); \
CLtmp->SRCip.s_addr = SIP.s_addr; \
CLtmp->DSTip.s_addr = DIP.s_addr; \
CLtmp->SRCport = SPORT; \
CLtmp->DSTport = DPORT; \
CLtmp->Length = MIN(LEN,MAXBUFLEN); \
bcopy( (u_char *)DATA, (u_char *)CLtmp->Data, CLtmp->Length); \
CLtmp->PKcnt = 1; \
CLtmp->Next = CLroot; \
CLtmp->Last = NULL; \
CLroot = CLtmp; \
}
register struct CREC *GET_NODE(Sip,SP,Dip,DP)
register struct in_addr Sip,Dip;
register u_int SP,DP;
{ register struct CREC *CLr = CLroot;
while(CLr != NULL) {
if( (CLr->SRCport == SP) && (CLr->DSTport == DP) &&
IPeq(CLr->SRCip,Sip) && IPeq(CLr->DSTip,Dip) )
break;
CLr = CLr->Next;
}
return(CLr);
}
#define ADDDATA_NODE(CL,DATA,LEN) { \
bcopy((u_char *)DATA, (u_char *)&CL->Data[CL->Length],LEN); \
CL->Length += LEN; \
}
#define PR_DATA(dp,ln) { \
register u_char lastc=0; \
while(ln-- >0) { \
if(*dp < 32) { \
switch(*dp) { \
case '\0': if((lastc=='\r') || (lastc=='\n') || lastc=='\0') \
break; \
case '\r': \
case '\n': fprintf(LOG,"\n : "); \
break; \
default : fprintf(LOG,"^%c", (*dp + 64)); \
break; \
} \
} else { \
if(isprint(*dp)) fputc(*dp,LOG); \
else fprintf(LOG,"(%d)",*dp); \
} \
lastc = *dp++; \
} \
fflush(LOG); \
}
void END_NODE(CLe,d,dl,msg)
register struct CREC *CLe;
register u_char *d;
register int dl;
register char *msg;
{
fprintf(LOG,"\n-- TCP/IP LOG -- TM: %s --\n", Ptm(&CLe->Time));
fprintf(LOG," PATH: %s(%s) =>",
Symaddr(CLe->SRCip),SERVp(CLe->SRCport));
fprintf(LOG," %s(%s)\n", Symaddr(CLe->DSTip),SERVp(CLe->DSTport));
fprintf(LOG," STAT: %s, %d pkts, %d bytes [%s]\n",
NOWtm(),CLe->PKcnt,(CLe->Length+dl),msg);
fprintf(LOG," DATA: ");
{ register u_int i = CLe->Length;
register u_char *p = CLe->Data;
PR_DATA(p,i);
PR_DATA(d,dl);
}
fprintf(LOG,"\n-- \n");
fflush(LOG);
if(CLe->Next != NULL)
CLe->Next->Last = CLe->Last;
if(CLe->Last != NULL)
CLe->Last->Next = CLe->Next;
else
CLroot = CLe->Next;
free(CLe);
}
/* 30 mins (x 60 seconds) */
#define IDLE_TIMEOUT 1800
#define IDLE_NODE() { \
time_t tm; \
time(&tm); \
if(LastTIME
register struct CREC *CLe,*CLt = CLroot; \
LastTIME=(tm+IDLE_TIMEOUT); tm-=IDLE_TIMEOUT; \
while(CLe=CLt) { \
CLt=CLe->Next; \
if(CLe->Time
END_NODE(CLe,(u_char *)NULL,0,"IDLE TIMEOUT"); \
} \
} \
}
void filter(cp, pktlen)
register char *cp;
register u_int pktlen;
{
register struct ip *ip;
register struct tcphdr *tcph;
{ register u_short EtherType=ntohs(((struct
ether_header *)cp)->ether_type);
if(EtherType < 0x600) {
EtherType = *(u_short *)(cp + SZETH + 6);
cp+=8; pktlen-=8;
}
From: Harlequin
Subject: alt.2600 FAQ Revision .014 (2/4)
Date: 27 August 1999 07:34
if(EtherType != ETHERTYPE_IP) /* chuk it if its not IP */
return;
}
/* ugh, gotta do an alignment :-( */
bcopy(cp + SZETH, (char *)Packet,(int)(pktlen - SZETH));
ip = (struct ip *)Packet;
if( ip->ip_p != IPPROTO_TCP) /* chuk non tcp pkts */
return;
tcph = (struct tcphdr *)(Packet + IPHLEN);
if(!( (TCPD == IPPORT_TELNET) ||
(TCPD == IPPORT_LOGINSERVER) ||
(TCPD == IPPORT_FTP)
)) return;
{ register struct CREC *CLm;
register int length = ((IPLEN - (IPHLEN * 4)) - (TCPOFF * 4));
register u_char *p = (u_char *)Packet;
p += ((IPHLEN * 4) + (TCPOFF * 4));
if(debug) {
fprintf(LOG,"PKT: (%s %04X) ", TCPflags(tcph->th_flags),length);
fprintf(LOG,"%s[%s] => ", inet_ntoa(IPS),SERVp(TCPS));
fprintf(LOG,"%s[%s]\n", inet_ntoa(IPD),SERVp(TCPD));
}
if( CLm = GET_NODE(IPS, TCPS, IPD, TCPD) ) {
CLm->PKcnt++;
if(length>0)
if( (CLm->Length + length) < MAXBUFLEN ) {
ADDDATA_NODE( CLm, p,length);
} else {
END_NODE( CLm, p,length, "DATA LIMIT");
}
if(TCPFL(TH_FIN|TH_RST)) {
END_NODE( CLm, (u_char *)NULL,0,
TCPFL(TH_FIN)?"TH_FIN":"TH_RST" );
}
} else {
if(TCPFL(TH_SYN)) {
ADD_NODE(IPS,IPD,TCPS,TCPD,p,length);
}
}
IDLE_NODE();
}
}
/* signal handler
*/
void death()
{ register struct CREC *CLe;
while(CLe=CLroot)
END_NODE( CLe, (u_char *)NULL,0, "SIGNAL");
fprintf(LOG,"\nLog ended at => %s\n",NOWtm());
fflush(LOG);
if(LOG != stdout)
fclose(LOG);
exit(1);
}
/* opens network interface, performs ioctls and reads from it,
* passing data to filter function
*/
void do_it()
{
int cc;
char *buf;
u_short sp_ts_len;
if(!(buf=malloc(CHUNKSIZE)))
Pexit(1,"Eth: malloc");
/* this /dev/nit initialization code pinched from etherfind */
{
struct strioctl si;
struct ifreq ifr;
struct timeval timeout;
u_int chunksize = CHUNKSIZE;
u_long if_flags = NI_PROMISC;
if((if_fd = open(NIT_DEV, O_RDONLY)) < 0)
Pexit(1,"Eth: nit open");
if(ioctl(if_fd, I_SRDOPT, (char *)RMSGD) < 0)
Pexit(1,"Eth: ioctl (I_SRDOPT)");
si.ic_timout = INFTIM;
if(ioctl(if_fd, I_PUSH, "nbuf") < 0)
Pexit(1,"Eth: ioctl (I_PUSH \"nbuf\")");
timeout.tv_sec = 1;
timeout.tv_usec = 0;
si.ic_cmd = NIOCSTIME;
si.ic_len = sizeof(timeout);
si.ic_dp = (char *)&timeout;
if(ioctl(if_fd, I_STR, (char *)&si) < 0)
Pexit(1,"Eth: ioctl (I_STR: NIOCSTIME)");
si.ic_cmd = NIOCSCHUNK;
si.ic_len = sizeof(chunksize);
si.ic_dp = (char *)&chunksize;
if(ioctl(if_fd, I_STR, (char *)&si) < 0)
Pexit(1,"Eth: ioctl (I_STR: NIOCSCHUNK)");
strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
ifr.ifr_name[sizeof(ifr.ifr_name) - 1] = '\0';
si.ic_cmd = NIOCBIND;
si.ic_len = sizeof(ifr);
si.ic_dp = (char *)𝔦
if(ioctl(if_fd, I_STR, (char *)&si) < 0)
Pexit(1,"Eth: ioctl (I_STR: NIOCBIND)");
si.ic_cmd = NIOCSFLAGS;
si.ic_len = sizeof(if_flags);
si.ic_dp = (char *)&if_flags;
if(ioctl(if_fd, I_STR, (char *)&si) < 0)
Pexit(1,"Eth: ioctl (I_STR: NIOCSFLAGS)");
if(ioctl(if_fd, I_FLUSH, (char *)FLUSHR) < 0)
Pexit(1,"Eth: ioctl (I_FLUSH)");
}
while ((cc = read(if_fd, buf, CHUNKSIZE)) >= 0) {
register char *bp = buf,
*bufstop = (buf + cc);
while (bp < bufstop) {
register char *cp = bp;
register struct nit_bufhdr *hdrp;
hdrp = (struct nit_bufhdr *)cp;
cp += sizeof(struct nit_bufhdr);
bp += hdrp->nhb_totlen;
filter(cp, (u_long)hdrp->nhb_msglen);
}
}
Pexit((-1),"Eth: read");
}
/* Authorize your program, generate your own password and uncomment
here */
/* #define AUTHPASSWD "EloiZgZejWyms" */
void getauth()
{ char *buf,*getpass(),*crypt();
char pwd[21],prmpt[81];
strcpy(pwd,AUTHPASSWD);
sprintf(prmpt,"(%s)UP? ",ProgName);
buf=getpass(prmpt);
if(strcmp(pwd,crypt(buf,pwd)))
exit(1);
}
*/
void main(argc, argv)
int argc;
char **argv;
{
char cbuf[BUFSIZ];
struct ifconf ifc;
int s,
ac=1,
backg=0;
ProgName=argv[0];
/* getauth(); */
LOG=NULL;
device=NULL;
while((ac
register char ch = argv[ac++][1];
switch(toupper(ch)) {
case 'I': device=argv[ac++];
break;
case 'F': if(!(LOG=fopen((LogName=argv[ac++]),"a")))
Zexit(1,"Output file cant be opened\n");
break;
case 'B': backg=1;
break;
case 'D': debug=1;
break;
default : fprintf(ERR,
"Usage: %s [-b] [-d] [-i interface] [-f file]\n",
ProgName);
exit(1);
}
}
if(!device) {
if((s=socket(AF_INET, SOCK_DGRAM, 0)) < 0)
Pexit(1,"Eth: socket");
ifc.ifc_len = sizeof(cbuf);
ifc.ifc_buf = cbuf;
if(ioctl(s, SIOCGIFCONF, (char *)&ifc) < 0)
Pexit(1,"Eth: ioctl");
close(s);
device = ifc.ifc_req->ifr_name;
}
fprintf(ERR,"Using logical device %s [%s]\n",device,NIT_DEV);
fprintf(ERR,"Output to %s.%s%s",(LOG)?LogName:"stdout",
(debug)?" (debug)":"",(backg)?" Backgrounding ":"\n");
if(!LOG)
LOG=stdout;
signal(SIGINT, death);
signal(SIGTERM,death);
signal(SIGKILL,death);
signal(SIGQUIT,death);
if(backg && debug) {
fprintf(ERR,"[Cannot bg with debug on]\n");
backg=0;
}
if(backg) {
register int s;
if((s=fork())>0) {
fprintf(ERR,"[pid %d]\n",s);
exit(0);
} else if(s<0)
Pexit(1,"fork");
if( (s=open("/dev/tty",O_RDWR))>0 ) {
ioctl(s,TIOCNOTTY,(char *)NULL);
close(s);
}
}
fprintf(LOG,"\nLog started at => %s [pid %d]\n",NOWtm(),getpid());
fflush(LOG);
do_it();
}
---------------------------------------------------------------------------
B-06. What is an Internet Outdial?
An Internet outdial is a modem connected to the Internet than you can
use to dial out. Normal outdials will only call local numbers. A GOD
(Global OutDial) is capable of calling long distance. Outdials are an
inexpensive method of calling long distance BBS's.
---------------------------------------------------------------------------
B-07. What are some Internet Outdials?
This FAQ answer is excerpted from CoTNo #5:
Internet Outdial List v3.0
by Cavalier and DisordeR
Introduction
------------
There are several lists of Internet outdials floating around the net
these days. The following is a compilation of other lists, as well as
v2.0 by DeadKat(CoTNo issue 2, article 4). Unlike other lists where the
author just ripped other people and released it, we have sat down and
tested each one of these. Some of them we have gotten "Connection
Refused" or it timed out while trying to connect...these have been
labeled dead.
Working Outdials
----------------
as of 12/29/94
NPA IP Address Instructions
--- ---------- ------------
215 isn.upenn.edu modem
217 dialout.cecer.army.mil atdt x,xxxXXXXX
218 modem.d.umn.edu atdt9,xxxXXXX
303 yuma.acns.colostate.edu 3020
412 myriad.pc.cc.cmu.edu 2600 Press D at the prompt
412 gate.cis.pitt.edu tn3270,
connect dialout.pitt.edu,
atdtxxxXXXX
413 dialout2400.smith.edu Ctrl } gets ENTER NUMBER: xxxxxxx
502 outdial.louisville.edu
502 uknet.uky.edu connect kecnet
@ dial: "outdial2400 or out"
602 acssdial.inre.asu.edu atdt8,,,,,[x][yyy]xxxyyyy
614 ns2400.acs.ohio-state.edu
614 ns9600.acs.ohio-state.edu
713 128.249.27.153 atdt x,xxxXXXX
714 modem.nts.uci.edu atdt[area]0[phone]
804 ublan.virginia.edu connect hayes, 9,,xxx-xxxx
804 ublan2.acc.virginia.edu connect telnet
connect hayes
Need Password
-------------
204 dial.cc.umanitoba.ca
206 rexair.cac.washington.edu This is an unbroken password
303 yuma.ACNS.ColoState.EDU login: modem
404 128.140.1.239 .modem8|CR
415 annex132-1.EECS.Berkeley.EDU "dial1" or "dial2" or
"dialer1"
514 cartier.CC.UMontreal.CA externe,9+number
703 wal-3000.cns.vt.edu dial2400 -aa
Dead/No Connect
---------------
201 idsnet
202 modem.aidt.edu
204 umnet.cc.manitoba.ca "dial12" or "dial24"
206 dialout24.cac.washington.edu
207 modem-o.caps.maine.edu
212 B719-7e.NYU.EDU dial3/dial12/dial24
212 B719-7f.NYU.EDU dial3/dial12/dial24
212 DIALOUT-1.NYU.EDU dial3/dial12/dial24
212 FREE-138-229.NYU.EDU dial3/dial12/dial24
212 UP19-4b.NYU.EDU dial3/dial12/dial24
215 wiseowl.ocis.temple.edu "atz" "atdt 9xxxyyyy"
218 aa28.d.umn.edu "cli" "rlogin modem"
at "login:" type "modem"
218 modem.d.umn.edu Hayes 9,XXX-XXXX
301 dial9600.umd.edu
305 alcat.library.nova.edu
305 office.cis.ufl.edu
307 modem.uwyo.edu Hayes 0,XXX-XXXX
313 35.1.1.6 dial2400-aa or dial1200-aa
or dialout
402 dialin.creighton.edu
402 modem.criegthon.edu
404 broadband.cc.emory.edu ".modem8" or ".dialout"
408 dialout.scu.edu
408 dialout1200.scu.edu
408 dialout2400.scu.edu
408 dialout9600.scu.edu
413 dialout.smith.edu
414 modems.uwp.edu
416 annex132.berkely.edu atdt 9,,,,, xxx-xxxx
416 pacx.utcs.utoronto.ca modem
503 dialout.uvm.edu
513 dialout24.afit.af.mil
513 r596adi1.uc.edu
514 pacx.CC.UMontreal.CA externe#9 9xxx-xxxx
517 engdial.cl.msu.edu
602 dial9600.telcom.arizona.edu
603 dialout1200.unh.edu
604 dial24-nc00.net.ubc.ca
604 dial24-nc01.net.ubc.ca
604 dial96-np65.net.ubc.ca
604 gmodem.capcollege.bc.ca
604 hmodem.capcollege.bc.ca
609 128.119.131.11X (X= 1 - 4) Hayes
609 129.119.131.11x (x = 1 to 4)
609 wright-modem-1.rutgers.edu
609 wright-modem-2.rutgers.edu
612 modem_out12e7.atk.com
612 modem_out24n8.atk.com
614 ns2400.ircc.ohio-state.edu "dial"
615 dca.utk.edu dial2400 D 99k #
615 MATHSUN23.MATH.UTK.EDU dial 2400 d 99Kxxxxxxx
616 modem.calvin.edu
617 128.52.30.3 2400baud
617 dialout.lcs.mit.edu
617 dialout1.princeton.edu
617 isdn3.Princeton.EDU
617 jadwingymkip0.Princeton.EDU
617 lord-stanley.Princeton.EDU
617 mpanus.Princeton.EDU
617 mrmodem.wellesley.edu
617 old-dialout.Princeton.EDU
617 stagger.Princeton.EDU
617 sunshine-02.lcs.mit.edu
617 waddle.Princeton.EDU
619 128.54.30.1 atdt [area][phone]
619 dialin.ucsd.edu "dialout"
703 modem_pool.runet.edu
703 wal-3000.cns.vt.edu
713 128.249.27.154 "c modem96" "atdt 9xxx-xxxx"
or "Hayes"
713 modem12.bcm.tmc.edu
713 modem24.bcm.tmc.edu
713 modem24.bcm.tmc.edu
714 mdmsrv7.sdsu.edu atdt 8xxx-xxxx
714 modem24.nts.uci.edu
714 pub-gopher.cwis.uci.edu
801 dswitch.byu.edu "C Modem"
808 irmodem.ifa.hawaii.edu
902 star.ccs.tuns.ca "dialout"
916 129.137.33.72
916 cc-dnet.ucdavis.edu connect hayes/dialout
916 engr-dnet1.engr.ucdavis.edu UCDNET
??? 128.119.131.11X (1 - 4)
??? 128.200.142.5
??? 128.54.30.1 nue, X to discontinue, ? for Help
??? 128.6.1.41
??? 128.6.1.42
??? 129.137.33.72
??? 129.180.1.57
??? 140.112.3.2 ntu
??? annexdial.rz.uni-duesseldorf.de
??? dial96.ncl.ac.uk
??? dialout.plk.af.mil
??? ee21.ee.ncu.edu.tw cs8005
??? im.mgt.ncu.edu.tw guest
??? modem.cis.uflu.edu
??? modem.ireq.hydro.qc.ca
??? modems.csuohio.edu
??? sparc20.ncu.edu.tw u349633
??? sun2cc.nccu.edu.tw ?
??? ts-modem.une.oz.au
??? twncu865.ncu.edu.tw guest
??? vtnet1.cns.ut.edu "CALL" or "call"
Conclusion
----------
If you find any of the outdials to have gone dead, changed commands,
or require password, please let us know so we can keep this list as
accurate as possible. If you would like to add to the list, feel free
to mail us and it will be included in future versions of this list,
with your name beside it. Have fun...
[Editors note: Updates have been made to this document after
the original publication]
---------------------------------------------------------------------------
B-08. What port is XXX on?
The file /etc/services on most Unix machines lists the port
assignments for that machine. For a complete list of port
assignments, read RFC (Request For Comments) 1700 "Assigned Numbers"
---------------------------------------------------------------------------
B-09. What is an anonymous remailer?
This FAQ answer was written by Raph Levien:
An anonymous remailer is a system on the Internet that allows you to
send e-mail or post messages to Usenet anonymously.
There are two sorts of remailers in widespread use. The first is the
anon.penet.fi style, the second is the cypherpunk style. The remailer
at anon.penet.fi is immensely popular, with over 160,000 users over its
lifetime, and probably tens of thousands of messages per day. Its main
advantage is that it's so easy to use. The cypherpunks mailers, which
provide much better security, are becoming more popular, however, as
there is more awareness of them.
The user of the anon.penet.fi system first needs to get an anonymous id.
This is done either by sending mail to somebody who already has one (for
example, by replying to a post on Usenet), or sending mail to
ping@anon.penet.fi. In either case, penet will mail back the new anon
id, which looks like an123456@anon.penet.fi. If an123456 then sends
mail to another user of the system, then this is what happens:
1. The mail is transported to anon.penet.fi, which resides somewhere in
the vicinity of Espoo, Finland.
2. These steps are carried out by software running on anon.penet.fi.
Penet first looks up the email address of the sender in its
database, then replaces it with the numeric code. All other
information about the sender is removed.
3. Then, penet looks up the number of the recipient in the same
database, and replaces it with the actual email address.
4. Finally, it sends the mail to the actual email address of the
recipient.
There are variations on this scheme, such as posting to Usenet (in which
step 3 is eliminated), but that's the basic idea.
Where anon.penet.fi uses a secret database to match anon id's to actual
email addresses, the cypherpunks remailers use cryptography to hide the
actual identities. Let's say I want to send email to a real email
address, or post it to Usenet, but keep my identity completely hidden.
To send it through one remailer, this is what happens.
1. I encrypt the message and the recipient's address, using the public
key of the remailer of my choice.
2. I send the email to the remailer.
3. When the remailer gets the mail, it decrypts it using its private
key, revealing as plaintext the message and the recipient's address.
4. All information about the sender is removed.
5. Finally, it sends it to the recipient's email address.
If one trusts the remailer operator, this is good enough. However, the
whole point of the cypherpunks remailers is that you don't _have_ to
trust any one individual or system. So, people who want real security
use a chain of remailers. If any one remailer on the "chain" is honest,
then the privacy of the message is assured.
To use a chain of remailers, I first have to prepare the message, which
is nestled within multiple layers of encryption, like a Russian
matryoshka doll. Preparing such a message is tedious and error prone,
so many people use an automated tool such as my premail package.
Anyway, after preparing the message, it is sent to the first remailer in
the chain, which corresponds to the outermost layer of encryption. Each
remailer strips off one layer of encryption and sends the message to the
next, until it reaches the final remailer. At this point, only the
innermost layer of encryption remains. This layer is stripped off,
revealing the plaintext message and recipient for the first time. At
this point, the message is sent to its actual recipient.
Remailers exist in many locations. A typical message might go through
Canada, Holland, Berkeley, and Finland before ending up at its final
location.
Aside from the difficulty of preparing all the encrypted messages,
another drawback of the cypherpunk remailers is that they don't easily
allow responses to anonymous mail. All information about the sender is
stripped away, including any kind of return address. However the new
alias servers promise to change that. To use an alias server, one
creates a new email address (mine is raph@alpha.c2.org). Mail sent to
this new address will be untraceably forwarded to one's real address.
To set this up, one first encrypts one's own email address with multiple
layers of encryption. Then, using an encrypted channel, one sends the
encrypted address to the alias server, along with the nickname that one
would like. The alias server registers the encrypted address in the
database. The alias server then handles reply mail in much the same way
as anon.penet.fi, except that the mail is forwarded to the chain of
anonymous remailers.
For maximum security, the user can arrange it so that, at each link in
the chain, the remailer adds another layer of encryption to the message
while removing one layer from the email address. When the user finally
gets the email, it is encrypted in multiple layers. The matryoshka has
to be opened one doll at a time until the plaintext message hidden
inside is revealed.
One other point is that the remailers must be reliable in order for all
this to work. This is especially true when a chain of remailers is used
-- if any one of the remailers is not working, then the message will be
dropped. This is why I maintain a list of reliable remailers. By
choosing reliable remailers to start with, there is a good chance the
message will finally get there.
---------------------------------------------------------------------------
B-10. What are the addresses of some anonymous remailers?
To see a comprehensive list on anonymous remailers point your web
browser to http://anon.efga.org/~rlist/.
For more information regarding anonymous email, check out
http://web.rge.com/pub/security/cypherpunks/.
The following URL's allow you to send anonymous e-mail via the world
wide web:
http://www.anonymizer.com/email/remailer-power.cgi?to=
http://www.contrib.andrew.cmu.edu/~gurevich/anonymous-email/index.html
http://www.ozemail.com.au/~geoffk/anon/anon.html
---------------------------------------------------------------------------
B-11. What is 127.0.0.1?
127.0.0.1 is a loopback network connection. If you telnet, ftp, etc...
to it you are connected to your own machine.
[Note from Dan Mellem: 127.0.0.127 is commonly used as the loopback
address. H.]
---------------------------------------------------------------------------
B-12. How do I post to a moderated newsgroup?
Usenet messages consist of message headers and message bodies. The
message header tells the news software how to process the message.
Headers can be divided into two types, required and optional. Required
headers are ones like "From" and "Newsgroups." Without the required
headers, your message will not be posted properly.
One of the optional headers is the "Approved" header. To post to a
moderated newsgroup, simply add an Approved header line to your
message header. The header line should contain the newsgroup
moderators e-mail address. To see the correct format for your target
newsgroup, save a message from the newsgroup and then look at it using
any text editor.
A "Approved" header line should look like this:
Approved: voyager@sekurity.org
There cannot not be a blank line in the message header. A blank line
will cause any portion of the header after the blank line to be
interpreted as part of the message body.
For more information, read RFC 1036: Standard for Interchange of
USENET messages.
---------------------------------------------------------------------------
B-13. How do I post to Usenet via e-mail?
Through an e-mail->Usenet gateway. Send an a e-mail messages to
nic.funet.fi, address your mail to alt.2600@nic.funet.fi.
Here are a few e-mail->Usenet gateways:
group.name@news.demon.co.uk
group.name@charm.magnus.acs.ohio-state.edu
group.name@undergrad.math.uwaterloo.ca
group.name@nic.funet.fi
group.name.usenet@decwrl.dec.com
---------------------------------------------------------------------------
B-14. What is a firewall?
A firewall is a system that is set up to control traffic flow between
two networks. Firewalls are most commonly specially configured Unix
systems, but firewalls have also been built out of many other systems,
including systems designed specifically for use as firewalls. The most
common firewall today is CheckPoint FireWall-1, but competitions such as
Cisco's PIX are quickly catching up on CheckPoint.
Many people disagree on the definiton of a firewall, and in this
discussion I will use the term loosely.
One type of firewall is the packet filtering firewall. In a packet
filtering firewall, the firewall examines five characteristics of a
packet:
Source IP address
Source port
Destination IP address
Destination port
IP protocol (TCP or UDP)
Based upon rules configured into the firewall, the packet will either be
allowed through, rejected, or dropped. If the firewall rejects the
packet, it sends a message back to the sender letting him know that the
packet was rejected. If the packet was dropped, the firewall simply
does not respond to the packet. The sender must wait for the
communications to time out. Dropping packets instead of rejecting them
greatly increases the time required to scan your network. Packet
filtering firewalls operate on Layer 3 of the OSI model, the Network
Layer. Routers are a very common form of packet filtering firewall.
An improved form of the packet filtering firewall is a packet filtering
firewall with a stateful inspection engine. With this enhancement, the
firewall "remembers" conversations between systems. It is then
necessary to fully examine only the first packet of a conversation.
Another type of firewall is the application-proxy firewall. In a
proxying firewall, every packet is stopped at the firewall. The packet
is then examined and compared to the rules configured into the firewall.
If the packet passes the examinations, it is re-created and sent out.
Because each packet is destroyed and re-created, there is a potential
that an application-proxy firewall can prevent unknown attacks based
upon weaknesses in the TCP/IP protocol suite that would not be prevented
by a packet filtering firewall. The drawback is that a separate
application-proxy must be written for each application type being
proxied. You need an HTTP proxy for web traffic, an FTP proxy for file
transfers, a Gopher proxy for Gopher traffic, etc... Application-proxy
firewalls operate on Layer 7 of the OSI model, the Application Layer.
Application-gateway firewalls also operate on Layer 7 of the OSI model.
Application-gateway firewalls exist for only a few network applications.
A typical application-gateway firewall is a system where you must telnet
to one system in order telnet again to a system outside of the network.
Another type of application-proxy firewall are SOCKS firewalls. Where
normal application-proxy firewalls do not require modifications to
network clients, SOCKS firewalls requires specially modified network
clients. This means you have to modify every system on your internal
network which needs to communicate with the external network. On a
Windows or OS/2 system, this can be as easy as swapping a few DLL's.
---------------------------------------------------------------------------
B-15. How do I attack a remote network across the Internet?
On a theoretical level, attacking a remote network across the Internet
is very simple.
First, you research to discover all of the IP address ranges used by the
target. Search the web, search Usenet, search Internet, search RIPE,
search APNIC, search everywhere.
Second, you identify all hosts in those IP address ranges. This may be
as simple as pinging each possible host in those networks. Be warned,
however, that many hosts will be protected by firewalls that prvent ICMP
ECHO Requests (used by ping) from reaching them. Those hosts may still
have vulnerable services running on them.
Third, you identify all open ports on each of those hosts. For example,
one host may be providing dns, bootp, and time services. This is
normally done by "port scanning" the host. Port scanning UDP ports is
much slower than port scanning TCP ports. TCP ports will respond
negatively when they are not open. UDP ports require you to wait for a
timeout. You may choose to scan only known ports, or to scan only ports
below 1024, or to scan all 65,535 ports.
Fourth, you attack vulnerable services. If you see a time server
running and you know of a time server exploit, you try it out. Perhaps
the target is running an OS that is not vulnerable, or perhaps the
system administrator has patched the target host. Or, maybe you will
succeed. Vulnerability information can be gleaned from Internet WWW
sites or mailing lists, traded privately, or developed on your own.
---------------------------------------------------------------------------
B-16. What is a TCP sequence prediction attack?
TCP is a reliable connection-oriented layer 4 (Transport Layer)
protocol. Packet transfer between hosts is accomplished by the layers
below layer 4 and TCP takes responsibility to making certain the packets
are delivered to higher layers in the protocol stack in the correct
order. To accomplish this reordering task, TCP uses the sequence number
field.
To successfully mount a TCP sequence prediction attack, you must first
listen to communications between two systems, one of which is your
target system. Then, you issue packets from your system to the target
system with the source IP address of the trusted system that is
communicating with the target system.
The packets you issue must have the sequence numbers that the target
system is expecting. In addition, your packets must arrive before the
packets from the trusted system whose connection you are hijacking. To
accomplish this, it is often necessary to flood the trusted system off
of the network with some form of denial of service attack.
Once you have taken over the connection, you can send data to allow you
to access the target host using a normal TCP/IP connection. The most
simple way to do this is:
echo "+ +" > /.rhosts
This specific technique relies upon inherent weaknesses in the BSD Unix
`r` services. However, SunRPC, NFS, X-Windows, and many other services
which rely upon IP address authentication can be exploited with a TCP
sequence prediction attack.
An excerpt from RFC 793 concering the generation of TCP sequence
numbers:
When new connections are created, an initial sequence number
(ISN) generator is employed which selects a new 32 bit ISN. The
generator is bound to a (possibly fictitious) 32 bit clock whose
low order bit is incremented roughly every 4 microseconds. Thus,
the ISN cycles approximately every 4.55 hours. Since we assume
that segments will stay in the network no more than the Maximum
Segment Lifetime (MSL) and that the MSL is less than 4.55 hours
we can reasonably assume that ISN's will be unique.
The developers of the BSD Unix TCP/IP stack did not follow these
recommendations. TCP/IP stacks based upon BSD Unix increase the
sequence number by 128,000 every second and by 64,000 for every new TCP
connection. This is significantly more predictable than the algorithm
specified in the RFC.
TCP sequence prediction attacks are stopped by any router or firewall
that is configured not to allow packets from an internal IP address to
originate from an external interface.
TCP Header Format
-----------------
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data | |U|A|P|R|S|F| |
| Offset| Reserved |R|C|S|S|Y|I| Window |
| | |G|K|H|T|N|N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Urgent Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
