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The infamous IP aliasing code for ppp, modified to work as a runtime option

Browse Source 
(otherwise ppp's behavior remains unchanged) and documented by myself,
Steve Sims, Nate Williams, Martin Renters and god-only-knows who else. :-)
Submitted by:	nate
Obtained from:	Charles Mott <cmott@srv.net>
This commit is contained in:
Jordan K. Hubbard 1996-12-12 14:39:47 +00:00
parent 54c5d00f71
commit a9f484e520
15 changed files with 2738 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
usr.sbin/ppp/Makefile
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@ -1,10 +1,11 @@
# $Id: Makefile,v 1.8 1996/10/18 01:44:45 jkh Exp $
# $Id: Makefile,v 1.9 1996/10/18 03:47:51 jkh Exp $
PROG= ppp
SRCS= async.c auth.c ccp.c chap.c chat.c command.c filter.c fsm.c hdlc.c \
ip.c ipcp.c lcp.c lqr.c log.c main.c mbuf.c modem.c os.c \
pap.c pred.c route.c slcompress.c timer.c systems.c uucplock.c vars.c \
vjcomp.c arp.c passwdauth.c
vjcomp.c arp.c alias.c alias_db.c alias_ftp.c alias_util.c \
passwdauth.c
#CFLAGS+= -DHAVE_SHELL_CMD_WITH_ANY_MODE
CFLAGS += -Wall -DUSE_PERROR -DMSEXT -DPASSWDAUTH
LDADD += -lmd -lcrypt -lutil

112
usr.sbin/ppp/README.alias Normal file
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User PPP Packet Aliasing
0. Contents
1. Background
2. Setup
3. Future Development
1. Background
User ppp has embedded packet aliasing (IP masquerading) code.
When this capability is enabled by the "-alias" command line
option, the ppp host will automatically alias IP packets forwarded
from a local network so that they appear to come from the ppp
host machine. Incoming packets from the outside world are then
appropriately de-aliased.
The process of aliasing involves both the IP address as well as
TCP and UDP port numbers. ICMP packets can be aliased by either
their id or sequence numbers.
This software was specifically meant to support users who have
unregistered, private address IP networks (e.g. 192.168.0.x or
10.0.0.x addresses). The ppp host can act as a gateway for these
networks, and computers on the local area net will have some
degree of internet access without the need for a registered IP
address. Additionally, there will be no need for an internet
service provider to maintain routing tables for the local area
network.
A disadvantage of packet aliasing is that machines on the local
network, behind the ppp host, can establish tcp connections and
make udp inqiries (such as domain name service requests), but these
machines, other than the ppp host itself, are not visible from
the outside world. There is, in effect, a partial firewall.
A second disadvantage is that "IP encoding" protocols, which send
IP address or port information within the data stream, are not
supported unless exception code has been put in place. A workaround
for ftp, which is the most well known of the IP encoding protocols,
has been developed in this implementation, so users do not have
to depend on using the ftp passive mode, as is sometimes the case
with other masquerading solutions.
All standard, non-encoding TCP and UDP protocals are supported,
Examples of these protocols are http, gopher and telnet. The
standard UDP mode of RealAudio is not presently supported,
but the TCP mode does work correctly. IRC is reported by users
to work in some, but not all, modes.
The packet aliasing code also handle many ICMP messages. In
particular, ping and traceroute are supported.
2. Packet Aliasing Setup
It is recommended that correct ppp operation first be verified
without packet aliasing enabled. Then ppp can be started with
the "-alias" option in the command line. Correct network operation
of the ppp host in packet aliasing mode should then be verified.
Finally, machines on the private network should be checked to see
whether they can access the internet.
Since the masquerading software aliases all packets, whether
they come from the host or another computer on the local area
network, a correctly operating ppp host will indicate that the
software should work properly for other computers on the private
network.
If the ppp host can access the internet, but other computers on
the local network cannot do this, then it should be checked that
IP forwarding is enabled on the ppp host and that the other
computers use this machine as a gateway. Of course, proper
communications between machines within the local area network
should also be verified (do they use consistent subnet addresses
and masks?).
3. Future Development
What is called packet aliasing here has been variously called
masquerading, network address translation (NAT) and transparent
proxying by others. It is an extremely useful function to
many users, but it is also necessarily imperfect. Workarounds
(hacks) are always needed for the occasional IP-encoding
protocols.
The specific solution implemented here does not block off or
reserve any segment of TCP or UDP ports on the ppp host for use
by the masquerading function. No communication to the kernel
is needed in this matter. All packets are aliased, whether
they originate from the ppp host or other computers on the
local network. This is a central issue, and some programmers
may wish to handle this differently.
The packet aliasing engine (alias.c, alias_db.c, alias_ftp.c
and alias_util.c) runs in user space, and is intended to be
both portable and reusable for interfaces other than ppp. The
basic engine is accessed by four simple function calls
(initialization, communication of host address, outgoing
aliasing and incoming de-aliasing).
Limited IP fragment handling exists. Once the packet aliasing
software sees the header fragment of a packet, all other fragments
will be correctly forwarded. However, if the header fragment
does not come first, then some fragments will be lost.
Charles Mott (cmott@srv.net)
December 4, 1996

112
usr.sbin/ppp/README.nat Normal file
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User PPP Packet Aliasing
0. Contents
1. Background
2. Setup
3. Future Development
1. Background
User ppp has embedded packet aliasing (IP masquerading) code.
When this capability is enabled by the "-alias" command line
option, the ppp host will automatically alias IP packets forwarded
from a local network so that they appear to come from the ppp
host machine. Incoming packets from the outside world are then
appropriately de-aliased.
The process of aliasing involves both the IP address as well as
TCP and UDP port numbers. ICMP packets can be aliased by either
their id or sequence numbers.
This software was specifically meant to support users who have
unregistered, private address IP networks (e.g. 192.168.0.x or
10.0.0.x addresses). The ppp host can act as a gateway for these
networks, and computers on the local area net will have some
degree of internet access without the need for a registered IP
address. Additionally, there will be no need for an internet
service provider to maintain routing tables for the local area
network.
A disadvantage of packet aliasing is that machines on the local
network, behind the ppp host, can establish tcp connections and
make udp inqiries (such as domain name service requests), but these
machines, other than the ppp host itself, are not visible from
the outside world. There is, in effect, a partial firewall.
A second disadvantage is that "IP encoding" protocols, which send
IP address or port information within the data stream, are not
supported unless exception code has been put in place. A workaround
for ftp, which is the most well known of the IP encoding protocols,
has been developed in this implementation, so users do not have
to depend on using the ftp passive mode, as is sometimes the case
with other masquerading solutions.
All standard, non-encoding TCP and UDP protocals are supported,
Examples of these protocols are http, gopher and telnet. The
standard UDP mode of RealAudio is not presently supported,
but the TCP mode does work correctly. IRC is reported by users
to work in some, but not all, modes.
The packet aliasing code also handle many ICMP messages. In
particular, ping and traceroute are supported.
2. Packet Aliasing Setup
It is recommended that correct ppp operation first be verified
without packet aliasing enabled. Then ppp can be started with
the "-alias" option in the command line. Correct network operation
of the ppp host in packet aliasing mode should then be verified.
Finally, machines on the private network should be checked to see
whether they can access the internet.
Since the masquerading software aliases all packets, whether
they come from the host or another computer on the local area
network, a correctly operating ppp host will indicate that the
software should work properly for other computers on the private
network.
If the ppp host can access the internet, but other computers on
the local network cannot do this, then it should be checked that
IP forwarding is enabled on the ppp host and that the other
computers use this machine as a gateway. Of course, proper
communications between machines within the local area network
should also be verified (do they use consistent subnet addresses
and masks?).
3. Future Development
What is called packet aliasing here has been variously called
masquerading, network address translation (NAT) and transparent
proxying by others. It is an extremely useful function to
many users, but it is also necessarily imperfect. Workarounds
(hacks) are always needed for the occasional IP-encoding
protocols.
The specific solution implemented here does not block off or
reserve any segment of TCP or UDP ports on the ppp host for use
by the masquerading function. No communication to the kernel
is needed in this matter. All packets are aliased, whether
they originate from the ppp host or other computers on the
local network. This is a central issue, and some programmers
may wish to handle this differently.
The packet aliasing engine (alias.c, alias_db.c, alias_ftp.c
and alias_util.c) runs in user space, and is intended to be
both portable and reusable for interfaces other than ppp. The
basic engine is accessed by four simple function calls
(initialization, communication of host address, outgoing
aliasing and incoming de-aliasing).
Limited IP fragment handling exists. Once the packet aliasing
software sees the header fragment of a packet, all other fragments
will be correctly forwarded. However, if the header fragment
does not come first, then some fragments will be lost.
Charles Mott (cmott@srv.net)
December 4, 1996

833
usr.sbin/ppp/alias.c Normal file
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/*
Alias.c provides supervisory control for the functions of the
packet aliasing software. It consists of routines to monitor
TCP connection state, protocol-specific aliasing routines,
limited fragment handling and the two primary outside world
functional interfaces: PacketAliasIn and PacketAliasOut.
The other C program files are briefly described. The data
structure framework which holds information needed to translate
packets is encapsulated in alias_db.c. Data is accessed by
function calls, so other segments of the program need not
know about the underlying data structures. Alias_ftp.c contains
special code for modifying the ftp PORT command used to establish
data connections. Alias_util.c contains a few utility routines.
This software is placed into the public domain with no restrictions
on its distribution.
Version 1.0 August, 1996 (cjm)
Version 1.1 August 20, 1996 (cjm)
PPP host accepts incoming connections for ports 0 to 1023.
Version 1.2 September 7, 1996 (cjm)
Fragment handling error in alias_db.c corrected.
Version 1.4 September 16, 1996 (cjm)
- A more generalized method for handling incoming
connections, without the 0-1023 restriction, is
implemented in alias_db.c
- Improved ICMP support in alias.c. Traceroute
packet streams can now be correctly aliased.
- TCP connection closing logic simplified in
alias.c and now allows for additional 1 minute
"grace period" after FIN or RST is observed.
Version 1.5 September 17, 1996 (cjm)
Corrected error in handling incoming UDP packets with 0 checksum.
Version 1.6 September 18, 1996 (cjm)
Simplified ICMP aliasing scheme. Should now support
traceroute from Win95 as well as FreeBSD.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/param.h>
#include <sys/types.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include <arpa/inet.h>
#include "alias.p"
#define FTP_CONTROL_PORT_NUMBER 21
/* TCP Handling Routines
TcpMonitorIn() -- These routines monitor TCP connections, and
TcpMonitorOut() -- delete a link node when a connection is closed.
These routines look for SYN, ACK and RST flags to determine when TCP
connections open and close. When a TCP connection closes, the data
structure containing packet aliasing information is deleted after
a timeout period.
*/
void
TcpMonitorIn(pip, link)
struct ip *pip;
char *link;
{
struct tcphdr *tc;
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
switch (GetStateIn(link))
{
case 0:
if (tc->th_flags & TH_SYN) SetStateIn(link, 1);
break;
case 1:
if (tc->th_flags & TH_FIN
|| tc->th_flags & TH_RST) SetStateIn(link, 2);
}
}
void
TcpMonitorOut(pip, link)
struct ip *pip;
char *link;
{
struct tcphdr *tc;
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
switch (GetStateOut(link))
{
case 0:
if (tc->th_flags & TH_SYN) SetStateOut(link, 1);
break;
case 1:
if (tc->th_flags & TH_FIN
|| tc->th_flags & TH_RST) SetStateOut(link, 2);
}
}
/* Protocol Specific Packet Aliasing Routines
IcmpAliasIn(), IcmpAliasIn1(), IcmpAliasIn2
IcmpAliasOut(), IcmpAliasOut1()
UdpAliasIn(), UdpAliasOut()
TcpAliasIn(), TcpAliasOut()
These routines handle protocol specific details of packet aliasing.
One may observe a certain amount of repetitive arithmetic in these
functions, the purpose of which is to compute a revised checksum
without actually summing over the entire data packet, which could be
unnecessarily time consuming.
The purpose of the packet aliasing routines is to replace the source
address of the outgoing packet and then correctly put it back for
any incoming packets. For TCP and UDP, ports are also re-mapped.
For ICMP echo/timestamp requests and replies, the following scheme
is used: the sequence number is replaced by an alias for the outgoing
packet and this sequence number, plus the id and remote address are
used to find the packet on the return path.
ICMP error messages are handled by looking at the IP fragment
in the data section of the message.
For TCP and UDP protocols, a port number is chosen for an outgoing
packet, and then incoming packets are identified by IP address and
port number. For TCP packets, there is additional logic in the event
that sequence and ack numbers have been altered (as is the case for
FTP data port commands).
The port numbers used by the packet aliasing module are not true
ports in the Unix sense. No sockets are actually bound to ports.
They are more correctly placeholders.
All packets are aliased, whether they come from the gateway machine
or other machines on a local area network.
*/
void
IcmpAliasIn1(pip)
struct ip *pip;
{
/*
Un-alias incoming echo and timestamp replies
*/
char *link;
struct icmp *ic;
ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
/* Get source address from ICMP data field and restore original data */
link = FindIcmpIn(pip->ip_src, ic->icmp_id, ic->icmp_seq);
if (link != NULL_PTR)
{
u_short original_seq;
int accumulate;
original_seq = GetOriginalPort(link);
/* Adjust ICMP checksum */
accumulate = ic->icmp_cksum;
accumulate += ic->icmp_seq;
accumulate -= original_seq;
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) accumulate;
}
/* Put original sequence number back in */
ic->icmp_seq = original_seq;
/* Put original address back into IP header */
pip->ip_dst = GetOriginalAddress(link);
/* Delete unneeded data structure */
DeleteLink(link);
}
}
void
IcmpAliasIn2(pip)
struct ip *pip;
{
/*
Alias incoming ICMP error messages containing
IP header and first 64 bits of datagram.
*/
struct ip *ip;
struct icmp *ic, *ic2;
struct udphdr *ud;
struct tcphdr *tc;
char *link;
ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
ip = (struct ip *) ic->icmp_data;
ud = (struct udphdr *) ((char *) ip + (ip->ip_hl <<2));
tc = (struct tcphdr *) ud;
ic2 = (struct icmp *) ud;
if (ip->ip_p == IPPROTO_UDP)
link = FindUdpIn(ip->ip_dst, ud->uh_dport, ud->uh_sport);
else if (ip->ip_p == IPPROTO_TCP)
link = FindTcpIn(ip->ip_dst, tc->th_dport, tc->th_sport);
else if (ip->ip_p == IPPROTO_ICMP)
if (ic2->icmp_type == ICMP_ECHO || ic2->icmp_type == ICMP_TSTAMP)
link = FindIcmpIn(ip->ip_dst, ic2->icmp_id, ic2->icmp_seq);
else
link = NULL_PTR;
else
link = NULL_PTR;
if (link != NULL_PTR)
{
if (ip->ip_p == IPPROTO_UDP || ip->ip_p == IPPROTO_TCP)
{
u_short *sptr;
int accumulate;
struct in_addr original_address;
u_short original_port;
original_address = GetOriginalAddress(link);
original_port = GetOriginalPort(link);
/* Adjust ICMP checksum */
accumulate = ic->icmp_cksum;
sptr = (u_short *) &(ip->ip_src);
accumulate += *sptr++;
accumulate += *sptr;
sptr = (u_short *) &original_address;
accumulate -= *sptr++;
accumulate -= *sptr;
accumulate += ud->uh_sport;
accumulate -= original_port;
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) accumulate;
}
/* Un-alias address in IP header */
pip->ip_dst = original_address;
/* Un-alias address and port number of original IP packet
fragment contained in ICMP data section */
ip->ip_src = original_address;
ud->uh_sport = original_port;
}
else if (pip->ip_p == IPPROTO_ICMP)
{
u_short *sptr;
int accumulate;
struct in_addr original_address;
u_short original_seq;
original_address = GetOriginalAddress(link);
original_seq = GetOriginalPort(link);
/* Adjust ICMP checksum */
accumulate = ic->icmp_cksum;
sptr = (u_short *) &(ip->ip_src);
accumulate += *sptr++;
accumulate += *sptr;
sptr = (u_short *) &original_address;
accumulate -= *sptr++;
accumulate -= *sptr;
accumulate += ic2->icmp_seq;
accumulate -= original_seq;
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) accumulate;
}
/* Un-alias address in IP header */
pip->ip_dst = original_address;
/* Un-alias address of original IP packet and seqence number of
embedded icmp datagram */
ip->ip_src = original_address;
ic2->icmp_seq = original_seq;
}
}
}
void
IcmpAliasIn(pip)
struct ip *pip;
{
struct icmp *ic;
ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
switch (ic->icmp_type)
{
case ICMP_ECHOREPLY:
case ICMP_TSTAMPREPLY:
if (ic->icmp_code == 0)
{
IcmpAliasIn1(pip);
}
break;
case ICMP_UNREACH:
case ICMP_SOURCEQUENCH:
case ICMP_TIMXCEED:
case ICMP_PARAMPROB:
IcmpAliasIn2(pip);
break;
}
}
void
IcmpAliasOut1(pip)
struct ip *pip;
{
/*
Alias ICMP echo and timestamp packets
*/
char *link;
struct icmp *ic;
ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
/* Save overwritten data for when echo packet returns */
link = FindIcmpOut(pip->ip_src, pip->ip_dst, ic->icmp_id, ic->icmp_seq);
if (link != NULL_PTR)
{
u_short alias_seq;
int accumulate;
alias_seq = GetAliasPort(link);
/* Since data field is being modified, adjust ICMP checksum */
accumulate = ic->icmp_cksum;
accumulate += ic->icmp_seq;
accumulate -= alias_seq;
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ic->icmp_cksum = (u_short) accumulate;
}
/* Alias sequence number */
ic->icmp_seq = alias_seq;
/* Change source address */
pip->ip_src = GetAliasAddress();
}
}
void
IcmpAliasOut(pip)
struct ip *pip;
{
struct icmp *ic;
ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
switch (ic->icmp_type)
{
case ICMP_ECHO:
case ICMP_TSTAMP:
if (ic->icmp_code == 0)
{
IcmpAliasOut1(pip);
}
break;
}
}
void
UdpAliasIn(pip)
struct ip *pip;
{
struct udphdr *ud;
char *link;
ud = (struct udphdr *) ((char *) pip + (pip->ip_hl << 2));
link = FindUdpIn(pip->ip_src, ud->uh_sport, ud->uh_dport);
if (link != NULL_PTR)
{
struct in_addr alias_address;
u_short alias_port;
int accumulate;
u_short *sptr;
alias_address = GetAliasAddress();
pip->ip_dst = GetOriginalAddress(link);
alias_port = ud->uh_dport;
ud->uh_dport = GetOriginalPort(link);
/* If UDP checksum is not zero, then adjust since destination port */
/* is being unaliased and destination port is being altered. */
if (ud->uh_sum != 0)
{
accumulate = ud->uh_sum;
accumulate += alias_port;
accumulate -= ud->uh_dport;
sptr = (u_short *) &alias_address;
accumulate += *sptr++;
accumulate += *sptr;
sptr = (u_short *) &(pip->ip_dst);
accumulate -= *sptr++;
accumulate -= *sptr;
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ud->uh_sum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ud->uh_sum = (u_short) accumulate;
}
}
}
}
void
UdpAliasOut(pip)
struct ip *pip;
{
struct udphdr *ud;
char *link;
ud = (struct udphdr *) ((char *) pip + (pip->ip_hl << 2));
link = FindUdpOut(pip->ip_src, pip->ip_dst, ud->uh_sport, ud->uh_dport);
if (link != NULL_PTR)
{
u_short alias_port;
alias_port = GetAliasPort(link);
/* If UDP checksum is not zero, adjust since source port is */
/* being aliased and source address is being altered */
if (ud->uh_sum != 0)
{
struct in_addr alias_address;
int accumulate;
u_short *sptr;
alias_address = GetAliasAddress();
accumulate = ud->uh_sum;
accumulate += ud->uh_sport;
accumulate -= alias_port;
sptr = (u_short *) &(pip->ip_src);
accumulate += *sptr++;
accumulate += *sptr;
sptr = (u_short *) &alias_address;
accumulate -= *sptr++;
accumulate -= *sptr;
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ud->uh_sum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
ud->uh_sum = (u_short) accumulate;
}
}
/* Put alias port in TCP header */
ud->uh_sport = alias_port;
/* Change source address */
pip->ip_src = GetAliasAddress();
}
}
void
TcpAliasIn(pip)
struct ip *pip;
{
struct tcphdr *tc;
char *link;
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
link = FindTcpIn(pip->ip_src, tc->th_sport, tc->th_dport);
if (link != NULL_PTR)
{
struct in_addr alias_address;
u_short alias_port;
int accumulate;
u_short *sptr;
alias_address = GetAliasAddress();
pip->ip_dst = GetOriginalAddress(link);
alias_port = tc->th_dport;
tc->th_dport = GetOriginalPort(link);
/* Adjust TCP checksum since destination port is being unaliased */
/* and destination port is being altered. */
accumulate = tc->th_sum;
accumulate += alias_port;
accumulate -= tc->th_dport;
sptr = (u_short *) &alias_address;
accumulate += *sptr++;
accumulate += *sptr;
sptr = (u_short *) &(pip->ip_dst);
accumulate -= *sptr++;
accumulate -= *sptr;
/* See if ack number needs to be modified */
if (GetAckModified(link) == 1)
{
int delta;
delta = GetDeltaAckIn(pip, link);
if (delta != 0)
{
sptr = (u_short *) &tc->th_ack;
accumulate += *sptr++;
accumulate += *sptr;
tc->th_ack = htonl(ntohl(tc->th_ack) - delta);
sptr = (u_short *) &tc->th_ack;
accumulate -= *sptr++;
accumulate -= *sptr;
}
}
/* Finish checksum modification */
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
tc->th_sum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
tc->th_sum = (u_short) accumulate;
}
/* Monitor TCP connection state */
TcpMonitorIn(pip, link);
}
}
void
TcpAliasOut(pip)
struct ip *pip;
{
struct tcphdr *tc;
char *link;
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
link = FindTcpOut(pip->ip_src, pip->ip_dst, tc->th_sport, tc->th_dport);
if (link !=NULL_PTR)
{
struct in_addr alias_address;
u_short alias_port;
int accumulate;
u_short *sptr;
alias_address = GetAliasAddress();
alias_port = GetAliasPort(link);
/* Monitor tcp connection state */
TcpMonitorOut(pip, link);
/* Special processing for ftp connection */
if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER
|| ntohs(tc->th_sport) == FTP_CONTROL_PORT_NUMBER)
HandleFtpOut(pip, link);
/* Adjust TCP checksum since source port is being aliased */
/* and source address is being altered */
accumulate = tc->th_sum;
accumulate += tc->th_sport;
accumulate -= alias_port;
sptr = (u_short *) &(pip->ip_src);
accumulate += *sptr++;
accumulate += *sptr;
sptr = (u_short *) &alias_address;
accumulate -= *sptr++;
accumulate -= *sptr;
/* Modify sequence number if necessary */
if (GetAckModified(link) == 1)
{
int delta;
delta = GetDeltaSeqOut(pip, link);
if (delta != 0)
{
sptr = (u_short *) &tc->th_seq;
accumulate += *sptr++;
accumulate += *sptr;
tc->th_seq = htonl(ntohl(tc->th_seq) + delta);
sptr = (u_short *) &tc->th_seq;
accumulate -= *sptr++;
accumulate -= *sptr;
}
}
/* Finish up checksum calculation */
if (accumulate < 0)
{
accumulate = -accumulate;
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
tc->th_sum = (u_short) ~accumulate;
}
else
{
accumulate = (accumulate >> 16) + (accumulate & 0xffff);
accumulate += accumulate >> 16;
tc->th_sum = (u_short) accumulate;
}
/* Put alias address in TCP header */
tc->th_sport = alias_port;
/* Change source address */
pip->ip_src = GetAliasAddress();
}
}
/* Fragment Handling
FragmentIn()
FragmentOut()
The packet aliasing module has a limited ability for handling IP
fragments. If the ICMP, TCP or UDP header is in the first fragment
received, then the id number of the IP packet is saved, and other
fragments are identified according to their ID number and IP address
they were sent from.
In general, fragments seem few and far between these days. One way
to generate them is with a ping request specifying a large data segment.
This is how the software here was tested.
In principle, out-of-order IP fragments could also be handled by saving
fragments until the header fragment came in and then sending them on
their way. However, this violates a basic interface rule of the
aliasing module in which individual packets are sent for remapping,
and nothing is actually known about how to write these packets to a
device interface.
*/
void
FragmentIn(pip)
struct ip *pip;
{
char *link;
link = FindFragmentIn2(pip->ip_src);
if (link != NULL_PTR)
GetFragmentAddr(link, pip->ip_id, pip->ip_p, &(pip->ip_dst) );
}
void
FragmentOut(pip)
struct ip *pip;
{
pip->ip_src = GetAliasAddress();
}
/* Outside World Access
PacketAliasIn()
PacketAliasOut()
*/
void
PacketAliasIn(pip)
struct ip *pip;
{
struct in_addr save_address;
/* Save initial destination address */
save_address = pip->ip_dst;
if ( (ntohs(pip->ip_off) & IP_OFFMASK) == 0 )
{
switch (pip->ip_p)
{
case IPPROTO_ICMP:
IcmpAliasIn(pip);
break;
case IPPROTO_UDP:
UdpAliasIn(pip);
break;
case IPPROTO_TCP:
TcpAliasIn(pip);
break;
}
if (ntohs(pip->ip_off) & IP_MF)
{
char *link;
link = FindFragmentIn1(pip->ip_src);
if (link != NULL_PTR)
SetFragmentData(link, pip->ip_id, pip->ip_p, pip->ip_dst);
}
}
else
{
FragmentIn(pip);
}
/* If destination address has changed, adjust IP checksum */
if (pip->ip_dst.s_addr != save_address.s_addr)
{
pip->ip_sum = 0;
pip->ip_sum = IpChecksum(pip);
}
}
void
PacketAliasOut(pip)
struct ip *pip;
{
struct in_addr save_address;
save_address = pip->ip_src;
if ((ntohs(pip->ip_off) & IP_OFFMASK) == 0)
{
switch (pip->ip_p)
{
case IPPROTO_ICMP:
IcmpAliasOut(pip);
break;
case IPPROTO_UDP:
UdpAliasOut(pip);
break;
case IPPROTO_TCP:
TcpAliasOut(pip);
break;
}
}
else
{
if (pip->ip_src.s_addr != GetAliasAddress().s_addr)
FragmentOut(pip);
}
/* Adjust IP checksum if source address has been aliased */
if (pip->ip_src.s_addr != save_address.s_addr)
{
pip->ip_sum = 0;
pip->ip_sum = IpChecksum(pip);
}
}

19
usr.sbin/ppp/alias.h Normal file
View File

@ -0,0 +1,19 @@
/*
Alias.h defines the outside world interfaces for the packet
aliasing software.
This software is placed into the public domain with no restrictions
on its distribution.
Initial version: August, 1996 (cjm)
*/
#ifndef _ALIAS_H_
#define _ALIAS_H_
extern void PacketAliasIn __P((char *));
extern void PacketAliasOut __P((char *));
extern void SetAliasAddress __P((struct in_addr));
extern void InitAlias();
extern void InitAliasLog();
#endif

94
usr.sbin/ppp/alias.p Normal file
View File

@ -0,0 +1,94 @@
/*
Alias.p contains the function prototypes for alias.c, alias_db.c,
alias_util.c and alias_ftp.c (as well as any future add-ons). It
is intended to be used only within the aliasing software. Outside
world interfaces are defined in alias.h
This software is placed into the public domain with no restrictions
on its distribution.
Initial version: August, 1996 (cjm)
*/
#define NULL_PTR 0
/* General utilities */
u_short InternetChecksum(u_short *, int);
u_short IpChecksum(struct ip *);
u_short TcpChecksum(struct ip *);
/* Data access utilities */
int StartPoint(struct in_addr, u_short, int);
u_short GetNewPort();
int SeqDiff(u_long, u_long);
void ShowAliasStats();
/* Internal data access */
void CleanupAliasData();
void IncrementalCleanup();
char * FindLink1(struct in_addr, struct in_addr, u_short, u_short, int);
char * FindLink2(struct in_addr, u_short, u_short, int);
void DeleteLink(char *);
char * AddLink(struct in_addr, struct in_addr, u_short, u_short,
u_short, int);
/* External data search */
char * FindIcmpIn(struct in_addr, u_short, u_short);
char * FindIcmpOut(struct in_addr, struct in_addr, u_short, u_short);
char * FindFragmentIn1(struct in_addr);
char * FindFragmentIn2(struct in_addr);
char * FindUdpIn(struct in_addr, u_short, u_short);
char * FindUdpOut(struct in_addr, struct in_addr, u_short, u_short);
char * FindTcpIn(struct in_addr, u_short, u_short);
char * FindTcpOut(struct in_addr, struct in_addr, u_short, u_short);
/* External data access/modification */
void GetIcmpData(char *, u_short, u_short, u_long *);
void SetIcmpData(char *, u_short, u_short, u_long);
void GetFragmentAddr(char *, u_short, u_char, struct in_addr *);
void SetFragmentData(char *, u_short, u_char, struct in_addr);
void SetStateIn(char *, int);
void SetStateOut(char *, int);
int GetStateIn(char *);
int GetStateOut(char *);
struct in_addr GetOriginalAddress(char *);
struct in_addr GetDestAddress(char *);
struct in_addr GetAliasAddress();
u_short GetOriginalPort(char *);
u_short GetDestPort(char *);
u_short GetAliasPort(char *);
void SetAckModified(char *);
int GetAckModified(char *);
int GetDeltaAckIn(struct ip *, char *);
int GetDeltaSeqOut(struct ip *, char *);
void AddSeq(struct ip *, char *, int);
/* Tcp specfic routines */
void TcpMonitorIn(struct ip *, char *);
void TcpMonitorOut(struct ip *, char *);
void HandleFtpOut(struct ip *, char *);
void NewFtpPortCommand(struct ip *, char *, struct in_addr, u_short);
/* Protocal specific packet aliasing routines */
void IcmpAliasIn1(struct ip *);
void IcmpAliasIn2(struct ip *);
void IcmpAliasIn(struct ip *);
void IcmpAliasOut(struct ip *);
void IcmpAliasOut1(struct ip *);
void UdpAliasIn(struct ip *);
void UdpAliasOut(struct ip *);
void TcpAliasIn(struct ip *);
void TcpAliasOut(struct ip *);
/* Fragment handling */
void FragmentIn(struct ip *);
void FragmentOut(struct ip *);
/* Outside world interfaces */
void PacketAliasIn(struct ip *);
void PacketAliasOut(struct ip *);
void SetAliasAddress(struct in_addr);
void InitAlias();
void InitAliasLog();

1145
usr.sbin/ppp/alias_db.c Normal file
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File diff suppressed because it is too large Load Diff

198
usr.sbin/ppp/alias_ftp.c Normal file
View File

@ -0,0 +1,198 @@
/*
Alias_ftp.c performs special processing for FTP sessions under
TCP. Specifically, when a PORT command from the client side
is sent, it is intercepted and modified. The address is changed
to the gateway machine and an aliasing port is used.
For this routine to work, the PORT command must fit entirely
into a single TCP packet. This is typically the case, but exceptions
can easily be envisioned under the actual specifications.
Probably the most troubling aspect of the approach taken here is
that the new PORT command will typically be a different length, and
this causes a certain amount of bookkeeping to keep track of the
changes of sequence and acknowledgment numbers, since the client
machine is totally unaware of the modification to the TCP stream.
This software is placed into the public domain with no restrictions
on its distribution.
Initial version: August, 1996 (cjm)
*/
/* Includes */
#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
/* Constants */
#define FTP_DATA_PORT_NUMBER 20
/* Prototypes */
#include "alias.p"
void
HandleFtpOut(pip, link)
struct ip *pip;
char *link;
{
int hlen, tlen, dlen;
struct in_addr true_addr;
u_short true_port;
char *sptr;
struct tcphdr *tc;
/* Calculate data length of TCP packet */
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
hlen = (pip->ip_hl + tc->th_off) << 2;
tlen = ntohs(pip->ip_len);
dlen = tlen - hlen;
/* Return is data length is too long or too short */
if (dlen<10 || dlen>80)
return;
/* Place string pointer and beginning of data */
sptr = (char *) pip;
sptr += hlen;
/* Parse through string using state diagram method */
{
char ch, zero;
int i, state;
u_long a1, a2, a3, a4;
u_short p1, p2;
a1=0; a2=0; a3=0; a4=0; p1=0; p2=0;
zero = '0';
state=-4;
for (i=0; i<dlen; i++)
{
ch = sptr[i];
switch (state)
{
case -4: if (ch == 'P') state=-3; else return; break;
case -3: if (ch == 'O') state=-2; else return; break;
case -2: if (ch == 'R') state=-1; else return; break;
case -1: if (ch == 'T') state= 0; else return; break;
case 0 :
if (isdigit(ch)) {a1=ch-zero; state=1 ;} break;
case 1 :
if (isdigit(ch)) a1=10*a1+ch-zero; else state=2 ; break;
case 2 :
if (isdigit(ch)) {a2=ch-zero; state=3 ;} break;
case 3 :
if (isdigit(ch)) a2=10*a2+ch-zero; else state=4 ; break;
case 4 :
if (isdigit(ch)) {a3=ch-zero; state=5 ;} break;
case 5 :
if (isdigit(ch)) a3=10*a3+ch-zero; else state=6 ; break;
case 6 :
if (isdigit(ch)) {a4=ch-zero; state=7 ;} break;
case 7 :
if (isdigit(ch)) a4=10*a4+ch-zero; else state=8 ; break;
case 8 :
if (isdigit(ch)) {p1=ch-zero; state=9 ;} break;
case 9 :
if (isdigit(ch)) p1=10*p1+ch-zero; else state=10; break;
case 10:
if (isdigit(ch)) {p2=ch-zero; state=11;} break;
case 11:
if (isdigit(ch)) p2=10*p2+ch-zero; break;
}
}
if (state == 11)
{
true_port = htons((p1<<8) + p2);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
NewFtpPortCommand(pip, link, true_addr, true_port);
}
}
}
void
NewFtpPortCommand(pip, link, true_addr, true_port)
struct ip *pip;
char *link;
struct in_addr true_addr;
u_short true_port;
{
char *ftp_link;
/* Establish link to address and port found in PORT command */
ftp_link = FindTcpOut (true_addr,
GetDestAddress(link),
true_port,
htons(FTP_DATA_PORT_NUMBER));
if (ftp_link != NULL_PTR)
{
int slen, hlen, tlen, dlen;
struct tcphdr *tc;
/* Calculate data length of TCP packet */
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
hlen = (pip->ip_hl + tc->th_off) << 2;
tlen = ntohs(pip->ip_len);
dlen = tlen - hlen;
/* Create new PORT command */
{
char stemp[80];
char *sptr;
u_short alias_port;
u_char *ptr;
int a1, a2, a3, a4, p1, p2;
struct in_addr aliasAddress;
/* Decompose alias address into quad format */
aliasAddress = GetAliasAddress();
ptr = (char *) &aliasAddress;
a1 = *ptr++; a2=*ptr++; a3=*ptr++; a4=*ptr;
/* Decompose alias port into pair format */
alias_port = GetAliasPort(ftp_link);
ptr = (char *) &alias_port;
p1 = *ptr++; p2=*ptr;
/* Generate command string */
sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
a1,a2,a3,a4,p1,p2);
/* Save string length for IP header modification */
slen = strlen(stemp);
/* Copy into IP packet */
sptr = (char *) pip; sptr += hlen;
strcpy(sptr, stemp);
}
/* Save information regarding modified seq and ack numbers */
{
int delta;
SetAckModified(link);
delta = GetDeltaSeqOut(pip, link);
AddSeq(pip, link, delta+slen-dlen);
pip->ip_len = ntohs(hlen + slen);
}
/* Compute TCP checksum for revised packet */
tc->th_sum = 0;
tc->th_sum = TcpChecksum(pip);
}
else
{
fprintf(stderr,
"PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n");
}
}

104
usr.sbin/ppp/alias_util.c Normal file
View File

@ -0,0 +1,104 @@
/*
Alias_util.h contains general utilities used by other functions
in the packet aliasing module. At the moment, there are functions
for computing IP header and TCP packet checksums.
The checksum routines are based upon example code in a Unix networking
text written by Stevens (sorry, I can't remember the title -- but
at least this is a good author).
Initial Version: August, 1996 (cjm)
*/
/*
Note: the checksum routines assume that the actual checksum word has
been zeroed out. If the checksum workd is filled with the proper value,
then these routines will give a result of zero (useful for testing
purposes);
*/
#include <sys/types.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
u_short
InternetChecksum(ptr, nbytes)
u_short *ptr;
int nbytes;
{
int sum, oddbyte;
sum = 0;
while (nbytes > 1)
{
sum += *ptr++;
nbytes -= 2;
}
if (nbytes == 1)
{
oddbyte = 0;
*((u_char *) &oddbyte) = *(u_char *) ptr;
sum += oddbyte;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
return(~sum);
}
u_short
IpChecksum(pip)
struct ip *pip;
{
return( InternetChecksum((u_short *) pip, (pip->ip_hl << 2)) );
}
u_short
TcpChecksum(pip)
struct ip *pip;
{
u_short *ptr;
struct tcphdr *tc;
int nhdr, ntcp, nbytes;
int sum, oddbyte;
nhdr = pip->ip_hl << 2;
ntcp = ntohs(pip->ip_len) - nhdr;
tc = (struct tcphdr *) ((char *) pip + nhdr);
ptr = (u_short *) tc;
/* Add up TCP header and data */
nbytes = ntcp;
sum = 0;
while (nbytes > 1)
{
sum += *ptr++;
nbytes -= 2;
}
if (nbytes == 1)
{
oddbyte = 0;
*((u_char *) &oddbyte) = *(u_char *) ptr;
sum += oddbyte;
}
/* "Pseudo-header" data */
ptr = (u_short *) &(pip->ip_dst);
sum += *ptr++;
sum += *ptr;
ptr = (u_short *) &(pip->ip_src);
sum += *ptr++;
sum += *ptr;
sum += htons((u_short) ntcp);
sum += htons((u_short) pip->ip_p);
/* Roll over carry bits */
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
/* Return checksum */
return((u_short) ~sum);
}

3
usr.sbin/ppp/defs.h
View File

@ -15,7 +15,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* $Id: defs.h,v 1.4 1995/10/08 14:57:28 amurai Exp $
* $Id: defs.h,v 1.5 1996/12/03 21:38:42 nate Exp $
*
* TODO:
*/
@ -60,6 +60,7 @@
#define MODE_DIRECT 4 /* Direct connection mode */
#define MODE_DEDICATED 8 /* Dedicated line mode */
#define MODE_DDIAL 16 /* Dedicated dialing line mode */
#define MODE_ALIAS 32 /* Packet aliasing (masquerading) */
#define EX_NORMAL 0
#define EX_START 1

8
usr.sbin/ppp/ip.c
View File

@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* $Id: ip.c,v 1.9 1996/05/11 20:48:25 phk Exp $
* $Id: ip.c,v 1.10 1996/12/03 21:38:45 nate Exp $
*
* TODO:
* o Return ICMP message for filterd packet
@ -34,6 +34,7 @@
#include <arpa/inet.h>
#include "vars.h"
#include "filter.h"
#include "alias.h"
extern void SendPppFrame();
extern void LcpClose();
@ -331,6 +332,11 @@ struct mbuf *bp; /* IN: Pointer to IP pakcet */
nb += wp->cnt;
}
if (mode & MODE_ALIAS) {
PacketAliasIn(tunbuff);
nb = ntohs(((struct ip *) tunbuff)->ip_len);
}
if ( PacketCheck(tunbuff, nb, FL_IN ) < 0) {
pfree(bp);
return;

5
usr.sbin/ppp/ipcp.c
View File

@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* $Id: ipcp.c,v 1.8 1996/05/11 20:48:26 phk Exp $
* $Id: ipcp.c,v 1.9 1996/10/06 13:32:28 jkh Exp $
*
* TODO:
* o More RFC1772 backwoard compatibility
@ -35,6 +35,7 @@
#include "os.h"
#include "phase.h"
#include "vars.h"
#include "alias.h"
extern void PutConfValue();
extern void Prompt();
@ -274,6 +275,8 @@ struct fsm *fp;
OsLinkup();
IpcpStartReport();
StartIdleTimer();
if (mode & MODE_ALIAS)
SetAliasAddress(IpcpInfo.want_ipaddr);
}
void

25
usr.sbin/ppp/main.c
View File

@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* $Id: main.c,v 1.22 1996/10/12 16:20:32 jkh Exp $
* $Id: main.c,v 1.23 1996/12/03 21:38:48 nate Exp $
*
* TODO:
* o Add commands for traffic summary, version display, etc.
@ -35,6 +35,8 @@
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include "modem.h"
#include "os.h"
#include "hdlc.h"
@ -46,6 +48,7 @@
#include "filter.h"
#include "systems.h"
#include "ip.h"
#include "alias.h"
#define LAUTH_M1 "Warning: No password entry for this host in ppp.secret\n"
#define LAUTH_M2 "Warning: All manipulation is allowed by anyone in the world\n"
@ -214,7 +217,7 @@ void
Usage()
{
fprintf(stderr,
"Usage: ppp [-auto | -direct | -dedicated | -ddial ] [system]\n");
"Usage: ppp [-auto | -direct | -dedicated | -ddial ] [ -alias ] [system]\n");
exit(EX_START);
}
@ -235,6 +238,10 @@ ProcessArgs(int argc, char **argv)
mode |= MODE_DEDICATED;
else if (strcmp(cp, "ddial") == 0)
mode |= MODE_DDIAL|MODE_AUTO;
else if (strcmp(cp, "alias") == 0) {
mode |= MODE_ALIAS;
optc--; /* this option isn't exclusive */
}
else
Usage();
optc++;
@ -274,6 +281,7 @@ char **argv;
Greetings();
GetUid();
IpcpDefAddress();
InitAlias();
if (SelectSystem("default", CONFFILE) < 0) {
fprintf(stderr, "Warning: No default entry is given in config file.\n");
@ -872,14 +880,23 @@ DoLoop()
if (LcpFsm.state <= ST_CLOSED && (mode & MODE_AUTO)) {
pri = PacketCheck(rbuff, n, FL_DIAL);
if (pri >= 0) {
if (mode & MODE_ALIAS) {
PacketAliasOut(rbuff);
n = ntohs(((struct ip *) rbuff)->ip_len);
}
IpEnqueue(pri, rbuff, n);
dial_up = TRUE; /* XXX */
dial_up = TRUE; /* XXX */
}
continue;
}
pri = PacketCheck(rbuff, n, FL_OUT);
if (pri >= 0)
if (pri >= 0) {
if (mode & MODE_ALIAS) {
PacketAliasOut(rbuff);
n = ntohs(((struct ip *) rbuff)->ip_len);
}
IpEnqueue(pri, rbuff, n);
}
}
}
logprintf("job done.\n");

45
usr.sbin/ppp/ppp.8
View File

@ -1,5 +1,5 @@
.\" manual page [] for ppp 0.94 beta2 + alpha
.\" $Id: ppp.8,v 1.19 1996/10/31 19:55:05 joerg Exp $
.\" $Id: ppp.8,v 1.20 1996/12/03 21:38:52 nate Exp $
.Dd 20 September 1995
.Os FreeBSD
.Dt PPP 8
@ -9,7 +9,8 @@
Point to Point Protocol (aka iijppp)
.Sh SYNOPSIS
.Nm
.Op Fl auto | ddial | dedicated | direct
.Op Fl auto | ddial | direct | dedicated
.Op Fl alias
.Op Ar system
.Sh DESCRIPTION
This is a user process
@ -53,13 +54,21 @@ will act as a daemon and wait for a packet to be sent over the
link. When this happens, the daemon automatically dials and establishes the
connection.
In almost the same manner ddial mode (dedicated dialing or demon dialing)
In almost the same manner ddial mode (dedicated or demon dialing)
also automatically dials and establishes the connection. However, it
differs in that it will dial the remote site any time it detects the
link is down, even if there are no packets to be sent. This mode is
useful for full-time connections who worry less about line charges
and more about being connected full time.
.It Supports packet aliasing.
Packet aliasing, more commonly known as masquerading, allows computers
on a private, unregistered network to access the internet. The
.Em PPP
host acts as a masquerading gateway. IP addresses as well as TCP and
UDP port numbers are aliased for outgoing packets and de-aliased for
returning packets.
.It Supports server-side PPP connections.
Can act as server which accepts incoming
.Em PPP
@ -380,6 +389,36 @@ You must use
.Dq quit all
to terminate the program as well.
.Sh PACKET ALIASING
The
.Fl alias
command line option enables packet aliasing. This allows the
ppp host to act as a masquerading gateway for other computers over
a local area network. Outgoing IP packets are are aliased so that
they appear to come from the ppp host, and incoming packets are
de-aliased so that they are routed to the correct machine on the
local area network.
Packet aliasing allows computers on private, unregistered
subnets to have internet access, although they are invisible
from the outside world.
In general, correct ppp operation should first be verified
with packet aliasing disabled. Then, the
.Fl alias
option should be switched on, and network applications (web browser,
telnet, ftp, ping, traceroute) should be checked on the ppp host.
Finally, the same or similar applications should be checked on other
computers in the LAN.
If network applications work correctly on the ppp host, but not on
other machines in the LAN, then the masquerading software is working
properly, but the host is either not forwarding or possibly receiving
IP packets. Check that IP forwarding is enabled in /etc/sysconfig
and that other machines have designated the ppp host as the gateway
for the LAN.
.Sh PACKET FILTERING
This implementation supports packet filtering. There are three kinds of

45
usr.sbin/ppp/ppp.8.m4
View File

@ -1,5 +1,5 @@
.\" manual page [] for ppp 0.94 beta2 + alpha
.\" $Id: ppp.8,v 1.19 1996/10/31 19:55:05 joerg Exp $
.\" $Id: ppp.8,v 1.20 1996/12/03 21:38:52 nate Exp $
.Dd 20 September 1995
.Os FreeBSD
.Dt PPP 8
@ -9,7 +9,8 @@
Point to Point Protocol (aka iijppp)
.Sh SYNOPSIS
.Nm
.Op Fl auto | ddial | dedicated | direct
.Op Fl auto | ddial | direct | dedicated
.Op Fl alias
.Op Ar system
.Sh DESCRIPTION
This is a user process
@ -53,13 +54,21 @@ will act as a daemon and wait for a packet to be sent over the
link. When this happens, the daemon automatically dials and establishes the
connection.
In almost the same manner ddial mode (dedicated dialing or demon dialing)
In almost the same manner ddial mode (dedicated or demon dialing)
also automatically dials and establishes the connection. However, it
differs in that it will dial the remote site any time it detects the
link is down, even if there are no packets to be sent. This mode is
useful for full-time connections who worry less about line charges
and more about being connected full time.
.It Supports packet aliasing.
Packet aliasing, more commonly known as masquerading, allows computers
on a private, unregistered network to access the internet. The
.Em PPP
host acts as a masquerading gateway. IP addresses as well as TCP and
UDP port numbers are aliased for outgoing packets and de-aliased for
returning packets.
.It Supports server-side PPP connections.
Can act as server which accepts incoming
.Em PPP
@ -380,6 +389,36 @@ You must use
.Dq quit all
to terminate the program as well.
.Sh PACKET ALIASING
The
.Fl alias
command line option enables packet aliasing. This allows the
ppp host to act as a masquerading gateway for other computers over
a local area network. Outgoing IP packets are are aliased so that
they appear to come from the ppp host, and incoming packets are
de-aliased so that they are routed to the correct machine on the
local area network.
Packet aliasing allows computers on private, unregistered
subnets to have internet access, although they are invisible
from the outside world.
In general, correct ppp operation should first be verified
with packet aliasing disabled. Then, the
.Fl alias
option should be switched on, and network applications (web browser,
telnet, ftp, ping, traceroute) should be checked on the ppp host.
Finally, the same or similar applications should be checked on other
computers in the LAN.
If network applications work correctly on the ppp host, but not on
other machines in the LAN, then the masquerading software is working
properly, but the host is either not forwarding or possibly receiving
IP packets. Check that IP forwarding is enabled in /etc/sysconfig
and that other machines have designated the ppp host as the gateway
for the LAN.
.Sh PACKET FILTERING
This implementation supports packet filtering. There are three kinds of