25.2. Using User PPP
前一頁 | 章 25. PPP and SLIP | 下一頁

## 25.2. Using User PPP

Updated and enhanced by Tom Rhodes.
Originally contributed by Brian Somers.
With input from Nik Clayton, Dirk Frömberg 且 Peter Childs.

### 25.2.1. User PPP

#### 25.2.1.1. Assumptions

This document assumes you have the following:

- An account with an Internet Service Provider (ISP) which you connect to using PPP.

- You have a modem or other device connected to your system and configured correctly which allows you to connect to your ISP.

- The dial-up number(s) of your ISP.

- Your login name and password. (Either a regular UNIX® style login and password pair, or a PAP or CHAP login and password pair.)

- The IP address of one or more name servers. Normally, you will be given two IP addresses by your ISP to use for this. If they have not given you at least one, then you can use the `enable dns` command in `ppp.conf` and ppp will set the name servers for you. This feature depends on your ISPs PPP implementation supporting DNS negotiation.

The following information may be supplied by your ISP, but is not completely necessary:

- The IP address of your ISP's gateway. The gateway is the machine to which you will connect and will be set up as your default route. If you do not have this information, we can make one up and your ISP's PPP server will tell us the correct value when we connect.

  This IP number is referred to as `HISADDR` by ppp.

- The netmask you should use. If your ISP has not provided you with one, you can safely use `255.255.255.255`.

- If your ISP provides you with a static IP address and hostname, you can enter it. Otherwise, we simply let the peer assign whatever IP address it sees fit.

If you do not have any of the required information, contact your ISP.

### 注意:

Throughout this section, many of the examples showing the contents of configuration files are numbered by line. These numbers serve to aid in the presentation and discussion only and are not meant to be placed in the actual file. Proper indentation with tab and space characters is also important.

#### 25.2.1.2. Creating PPP Device Nodes

Under normal circumstances, most users will only need one `tun` device (`/dev/tun0`). References to `tun0` below may be changed to `tun`N`` where `N` is any unit number corresponding to your system.

For FreeBSD installations that do not have devfs(5) enabled (FreeBSD 4.X and earlier), the existence of the `tun0` device should be verified (this is not necessary if devfs(5) is enabled as device nodes will be created on demand).

The easiest way to make sure that the `tun0` device is configured correctly is to remake the device. To remake the device, do the following:

`#` `cd /dev` `#` `sh MAKEDEV tun0`

If you need 16 tunnel devices in your kernel, you will need to create them. This can be done by executing the following commands:

`#` `cd /dev` `#` `sh MAKEDEV tun15`

#### 25.2.1.3. Automatic PPP Configuration

Both `ppp` and `pppd` (the kernel level implementation of PPP) use the configuration files located in the `/etc/ppp` directory. Examples for user ppp can be found in `/usr/share/examples/ppp/`.

Configuring `ppp` requires that you edit a number of files, depending on your requirements. What you put in them depends to some extent on whether your ISP allocates IP addresses statically (i.e., you get given one IP address, and always use that one) or dynamically (i.e., your IP address changes each time you connect to your ISP).

##### 25.2.1.3.1. PPP and Static IP Addresses

You will need to edit the `/etc/ppp/ppp.conf` configuration file. It should look similar to the example below.

### 注意:

Lines that end in a `:` start in the first column (beginning of the line)— all other lines should be indented as shown using spaces or tabs.

1 default: 2 set log Phase Chat LCP IPCP CCP tun command 3 ident user-ppp VERSION (built COMPILATIONDATE) 4 set device /dev/cuaa0 5 set speed 115200 6 set dial "ABORT BUSY ABORT NO\\sCARRIER TIMEOUT 5 \ 7 \"\" AT OK-AT-OK ATE1Q0 OK \\dATDT\\T TIMEOUT 40 CONNECT" 8 set timeout 180 9 enable dns 10 11 provider: 12 set phone "(123) 456 7890" 13 set authname foo 14 set authkey bar 15 set login "TIMEOUT 10 \"\" \"\" gin:--gin: \\U word: \\P col: ppp" 16 set timeout 300 17 set ifaddr `x.x.x.x` `y.y.y.y` 255.255.255.255 0.0.0.0 18 add default HISADDR

Line 1:

  Identifies the default entry. Commands in this entry are executed automatically when ppp is run.

Line 2:

  Enables logging parameters. When the configuration is working satisfactorily, this line should be reduced to saying

  set log phase tun

  in order to avoid excessive log file sizes.

Line 3:

  Tells PPP how to identify itself to the peer. PPP identifies itself to the peer if it has any trouble negotiating and setting up the link, providing information that the peers administrator may find useful when investigating such problems.

Line 4:

  Identifies the device to which the modem is connected. `COM1` is `/dev/cuaa0` and `COM2` is `/dev/cuaa1`.

Line 5:

  Sets the speed you want to connect at. If 115200 does not work (it should with any reasonably new modem), try 38400 instead.

Line 6 & 7:

  The dial string. User PPP uses an expect-send syntax similar to the chat(8) program. Refer to the manual page for information on the features of this language.

  Note that this command continues onto the next line for readability. Any command in `ppp.conf` may do this if the last character on the line is a ``\'' character.

Line 8:

  Sets the idle timeout for the link. 180 seconds is the default, so this line is purely cosmetic.

Line 9:

  Tells PPP to ask the peer to confirm the local resolver settings. If you run a local name server, this line should be commented out or removed.

Line 10:

  A blank line for readability. Blank lines are ignored by PPP.

Line 11:

  Identifies an entry for a provider called “provider”. This could be changed to the name of your ISP so that later you can use the `load ISP` to start the connection.

Line 12:

  Sets the phone number for this provider. Multiple phone numbers may be specified using the colon (`:`) or pipe character (`|`)as a separator. The difference between the two separators is described in ppp(8). To summarize, if you want to rotate through the numbers, use a colon. If you want to always attempt to dial the first number first and only use the other numbers if the first number fails, use the pipe character. Always quote the entire set of phone numbers as shown.

  You must enclose the phone number in quotation marks (`"`) if there is any intention on using spaces in the phone number. This can cause a simple, yet subtle error.

Line 13 & 14:

  Identifies the user name and password. When connecting using a UNIX® style login prompt, these values are referred to by the `set login` command using the \U and \P variables. When connecting using PAP or CHAP, these values are used at authentication time.

Line 15:

  If you are using PAP or CHAP, there will be no login at this point, and this line should be commented out or removed. See PAP and CHAP authentication for further details.

  The login string is of the same chat-like syntax as the dial string. In this example, the string works for a service whose login session looks like this:

  J. Random Provider login: `foo` password: `bar` protocol: ppp

  You will need to alter this script to suit your own needs. When you write this script for the first time, you should ensure that you have enabled “chat” logging so you can determine if the conversation is going as expected.

Line 16:

  Sets the default idle timeout (in seconds) for the connection. Here, the connection will be closed automatically after 300 seconds of inactivity. If you never want to timeout, set this value to zero or use the `-ddial` command line switch.

Line 17:

  Sets the interface addresses. The string `x.x.x.x` should be replaced by the IP address that your provider has allocated to you. The string `y.y.y.y` should be replaced by the IP address that your ISP indicated for their gateway (the machine to which you connect). If your ISP has not given you a gateway address, use `10.0.0.2/0`. If you need to use a “guessed” address, make sure that you create an entry in `/etc/ppp/ppp.linkup` as per the instructions for PPP and Dynamic IP addresses. If this line is omitted, `ppp` cannot run in `-auto` mode.

Line 18:

  Adds a default route to your ISP's gateway. The special word `HISADDR` is replaced with the gateway address specified on line 17. It is important that this line appears after line 17, otherwise `HISADDR` will not yet be initialized.

  If you do not wish to run ppp in `-auto`, this line should be moved to the `ppp.linkup` file.

It is not necessary to add an entry to `ppp.linkup` when you have a static IP address and are running ppp in `-auto` mode as your routing table entries are already correct before you connect. You may however wish to create an entry to invoke programs after connection. This is explained later with the sendmail example.

Example configuration files can be found in the `/usr/share/examples/ppp/` directory.

##### 25.2.1.3.2. PPP and Dynamic IP Addresses

If your service provider does not assign static IP addresses, `ppp` can be configured to negotiate the local and remote addresses. This is done by “guessing” an IP address and allowing `ppp` to set it up correctly using the IP Configuration Protocol (IPCP) after connecting. The `ppp.conf` configuration is the same as PPP and Static IP Addresses, with the following change:

17 set ifaddr 10.0.0.1/0 10.0.0.2/0 255.255.255.255

Again, do not include the line number, it is just for reference. Indentation of at least one space is required.

Line 17:

  The number after the `/` character is the number of bits of the address that ppp will insist on. You may wish to use IP numbers more appropriate to your circumstances, but the above example will always work.

  The last argument (`0.0.0.0`) tells PPP to start negotiations using address `0.0.0.0` rather than `10.0.0.1` and is necessary for some ISPs. Do not use `0.0.0.0` as the first argument to `set ifaddr` as it prevents PPP from setting up an initial route in `-auto` mode.

If you are not running in `-auto` mode, you will need to create an entry in `/etc/ppp/ppp.linkup`. `ppp.linkup` is used after a connection has been established. At this point, `ppp` will have assigned the interface addresses and it will now be possible to add the routing table entries:

1 provider: 2 add default HISADDR

Line 1:

  On establishing a connection, `ppp` will look for an entry in `ppp.linkup` according to the following rules: First, try to match the same label as we used in `ppp.conf`. If that fails, look for an entry for the IP address of our gateway. This entry is a four-octet IP style label. If we still have not found an entry, look for the `MYADDR` entry.

Line 2:

  This line tells `ppp` to add a default route that points to `HISADDR`. `HISADDR` will be replaced with the IP number of the gateway as negotiated by the IPCP.

See the `pmdemand` entry in the files `/usr/share/examples/ppp/ppp.conf.sample` and `/usr/share/examples/ppp/ppp.linkup.sample` for a detailed example.

##### 25.2.1.3.3. Receiving Incoming Calls

When you configure ppp to receive incoming calls on a machine connected to a LAN, you must decide if you wish to forward packets to the LAN. If you do, you should allocate the peer an IP number from your LAN's subnet, and use the command `enable proxy` in your `/etc/ppp/ppp.conf` file. You should also confirm that the `/etc/rc.conf` file contains the following:

gateway_enable="YES"

##### 25.2.1.3.4. Which getty?

Configuring FreeBSD for Dial-up Services provides a good description on enabling dial-up services using getty(8).

An alternative to `getty` is mgetty, a smarter version of `getty` designed with dial-up lines in mind.

The advantages of using `mgetty` is that it actively talks to modems, meaning if port is turned off in `/etc/ttys` then your modem will not answer the phone.

Later versions of `mgetty` (from 0.99beta onwards) also support the automatic detection of PPP streams, allowing your clients script-less access to your server.

Refer to Mgetty and AutoPPP for more information on `mgetty`.

##### 25.2.1.3.5. PPP Permissions

The `ppp` command must normally be run as the `root` user. If however, you wish to allow `ppp` to run in server mode as a normal user by executing `ppp` as described below, that user must be given permission to run `ppp` by adding them to the `network` group in `/etc/group`.

You will also need to give them access to one or more sections of the configuration file using the `allow` command:

allow users fred mary

If this command is used in the `default` section, it gives the specified users access to everything.

##### 25.2.1.3.6. PPP Shells for Dynamic-IP Users

Create a file called `/etc/ppp/ppp-shell` containing the following:

#!/bin/sh IDENT=`echo $0 | sed -e 's/^.*-\(.*\)$/\1/'` CALLEDAS="$IDENT" TTY=`tty` if [ x$IDENT = xdialup ]; then IDENT=`basename $TTY` fi echo "PPP for $CALLEDAS on $TTY" echo "Starting PPP for $IDENT" exec /usr/sbin/ppp -direct $IDENT

This script should be executable. Now make a symbolic link called `ppp-dialup` to this script using the following commands:

`#` `ln -s ppp-shell /etc/ppp/ppp-dialup`

You should use this script as the shell for all of your dialup users. This is an example from `/etc/passwd` for a dialup PPP user with username `pchilds` (remember do not directly edit the password file, use vipw(8)).

pchilds:*:1011:300:Peter Childs PPP:/home/ppp:/etc/ppp/ppp-dialup

Create a `/home/ppp` directory that is world readable containing the following 0 byte files:

-r--r--r-- 1 root wheel 0 May 27 02:23 .hushlogin -r--r--r-- 1 root wheel 0 May 27 02:22 .rhosts

which prevents `/etc/motd` from being displayed.

##### 25.2.1.3.7. PPP Shells for Static-IP Users

Create the `ppp-shell` file as above, and for each account with statically assigned IPs create a symbolic link to `ppp-shell`.

For example, if you have three dialup customers, `fred`, `sam`, and `mary`, that you route class C networks for, you would type the following:

`#` `ln -s /etc/ppp/ppp-shell /etc/ppp/ppp-fred` `#` `ln -s /etc/ppp/ppp-shell /etc/ppp/ppp-sam` `#` `ln -s /etc/ppp/ppp-shell /etc/ppp/ppp-mary`

Each of these users dialup accounts should have their shell set to the symbolic link created above (for example, `mary`'s shell should be `/etc/ppp/ppp-mary`).

##### 25.2.1.3.8. Setting Up `ppp.conf` for Dynamic-IP Users

The `/etc/ppp/ppp.conf` file should contain something along the lines of:

default: set debug phase lcp chat set timeout 0 ttyd0: set ifaddr 203.14.100.1 203.14.100.20 255.255.255.255 enable proxy ttyd1: set ifaddr 203.14.100.1 203.14.100.21 255.255.255.255 enable proxy

### 注意:

The indenting is important.

The `default:` section is loaded for each session. For each dialup line enabled in `/etc/ttys` create an entry similar to the one for `ttyd0:` above. Each line should get a unique IP address from your pool of IP addresses for dynamic users.

##### 25.2.1.3.9. Setting Up `ppp.conf` for Static-IP Users

Along with the contents of the sample `/usr/share/examples/ppp/ppp.conf` above you should add a section for each of the statically assigned dialup users. We will continue with our `fred`, `sam`, and `mary` example.

fred: set ifaddr 203.14.100.1 203.14.101.1 255.255.255.255 sam: set ifaddr 203.14.100.1 203.14.102.1 255.255.255.255 mary: set ifaddr 203.14.100.1 203.14.103.1 255.255.255.255

The file `/etc/ppp/ppp.linkup` should also contain routing information for each static IP user if required. The line below would add a route for the `203.14.101.0` class C via the client's ppp link.

fred: add 203.14.101.0 netmask 255.255.255.0 HISADDR sam: add 203.14.102.0 netmask 255.255.255.0 HISADDR mary: add 203.14.103.0 netmask 255.255.255.0 HISADDR

##### 25.2.1.3.10. `mgetty` and AutoPPP

Configuring and compiling `mgetty` with the `AUTO_PPP` option enabled allows `mgetty` to detect the LCP phase of PPP connections and automatically spawn off a ppp shell. However, since the default login/password sequence does not occur it is necessary to authenticate users using either PAP or CHAP.

This section assumes the user has successfully configured, compiled, and installed a version of `mgetty` with the `AUTO_PPP` option (v0.99beta or later).

Make sure your `/usr/local/etc/mgetty+sendfax/login.config` file has the following in it:

/AutoPPP/ - - /etc/ppp/ppp-pap-dialup

This will tell `mgetty` to run the `ppp-pap-dialup` script for detected PPP connections.

Create a file called `/etc/ppp/ppp-pap-dialup` containing the following (the file should be executable):

#!/bin/sh exec /usr/sbin/ppp -direct pap$IDENT

For each dialup line enabled in `/etc/ttys`, create a corresponding entry in `/etc/ppp/ppp.conf`. This will happily co-exist with the definitions we created above.

pap: enable pap set ifaddr 203.14.100.1 203.14.100.20-203.14.100.40 enable proxy

Each user logging in with this method will need to have a username/password in `/etc/ppp/ppp.secret` file, or alternatively add the following option to authenticate users via PAP from the `/etc/passwd` file.

enable passwdauth

If you wish to assign some users a static IP number, you can specify the number as the third argument in `/etc/ppp/ppp.secret`. See `/usr/share/examples/ppp/ppp.secret.sample` for examples.

##### 25.2.1.3.11. MS Extensions

It is possible to configure PPP to supply DNS and NetBIOS nameserver addresses on demand.

To enable these extensions with PPP version 1.x, the following lines might be added to the relevant section of `/etc/ppp/ppp.conf`.

enable msext set ns 203.14.100.1 203.14.100.2 set nbns 203.14.100.5

And for PPP version 2 and above:

accept dns set dns 203.14.100.1 203.14.100.2 set nbns 203.14.100.5

This will tell the clients the primary and secondary name server addresses, and a NetBIOS nameserver host.

In version 2 and above, if the `set dns` line is omitted, PPP will use the values found in `/etc/resolv.conf`.

##### 25.2.1.3.12. PAP and CHAP Authentication

Some ISPs set their system up so that the authentication part of your connection is done using either of the PAP or CHAP authentication mechanisms. If this is the case, your ISP will not give a `login:` prompt when you connect, but will start talking PPP immediately.

PAP is less secure than CHAP, but security is not normally an issue here as passwords, although being sent as plain text with PAP, are being transmitted down a serial line only. There is not much room for crackers to “eavesdrop”.

Referring back to the PPP and Static IP addresses or PPP and Dynamic IP addresses sections, the following alterations must be made:

13 set authname `MyUserName` 14 set authkey `MyPassword` 15 set login

Line 13:

  This line specifies your PAP/CHAP user name. You will need to insert the correct value for `MyUserName`.

Line 14:

  This line specifies your PAP/CHAP password. You will need to insert the correct value for `MyPassword`. You may want to add an additional line, such as:

  16 accept PAP

  or

  16 accept CHAP

  to make it obvious that this is the intention, but PAP and CHAP are both accepted by default.

Line 15:

  Your ISP will not normally require that you log into the server if you are using PAP or CHAP. You must therefore disable your “set login” string.

##### 25.2.1.3.13. Changing Your `ppp` Configuration on the Fly

It is possible to talk to the `ppp` program while it is running in the background, but only if a suitable diagnostic port has been set up. To do this, add the following line to your configuration:

set server /var/run/ppp-tun`%d` DiagnosticPassword 0177

This will tell PPP to listen to the specified UNIX® domain socket, asking clients for the specified password before allowing access. The `%d` in the name is replaced with the `tun` device number that is in use.

Once a socket has been set up, the pppctl(8) program may be used in scripts that wish to manipulate the running program.

#### 25.2.1.4. Using PPP Network Address Translation Capability

PPP has ability to use internal NAT without kernel diverting capabilities. This functionality may be enabled by the following line in `/etc/ppp/ppp.conf`:

nat enable yes

Alternatively, PPP NAT may be enabled by command-line option `-nat`. There is also `/etc/rc.conf` knob named `ppp_nat`, which is enabled by default.

If you use this feature, you may also find useful the following `/etc/ppp/ppp.conf` options to enable incoming connections forwarding:

nat port tcp 10.0.0.2:ftp ftp nat port tcp 10.0.0.2:http http

or do not trust the outside at all

nat deny_incoming yes

#### 25.2.1.5. Final System Configuration

You now have `ppp` configured, but there are a few more things to do before it is ready to work. They all involve editing the `/etc/rc.conf` file.

Working from the top down in this file, make sure the `hostname=` line is set, e.g.:

hostname="foo.example.com"

If your ISP has supplied you with a static IP address and name, it is probably best that you use this name as your host name.

Look for the `network_interfaces` variable. If you want to configure your system to dial your ISP on demand, make sure the `tun0` device is added to the list, otherwise remove it.

network_interfaces="lo0 tun0" ifconfig_tun0=

### 注意:

The `ifconfig_tun0` variable should be empty, and a file called `/etc/start_if.tun0` should be created. This file should contain the line:

ppp -auto mysystem

This script is executed at network configuration time, starting your ppp daemon in automatic mode. If you have a LAN for which this machine is a gateway, you may also wish to use the `-alias` switch. Refer to the manual page for further details.

Make sure that the router program is set to `NO` with the following line in your `/etc/rc.conf`:

router_enable="NO"

It is important that the `routed` daemon is not started, as `routed` tends to delete the default routing table entries created by `ppp`.

It is probably worth your while ensuring that the `sendmail_flags` line does not include the `-q` option, otherwise `sendmail` will attempt to do a network lookup every now and then, possibly causing your machine to dial out. You may try:

sendmail_flags="-bd"

The downside of this is that you must force `sendmail` to re-examine the mail queue whenever the ppp link is up by typing:

`#` `/usr/sbin/sendmail -q`

You may wish to use the `!bg` command in `ppp.linkup` to do this automatically:

1 provider: 2 delete ALL 3 add 0 0 HISADDR 4 !bg sendmail -bd -q30m

If you do not like this, it is possible to set up a “dfilter” to block SMTP traffic. Refer to the sample files for further details.

All that is left is to reboot the machine. After rebooting, you can now either type:

`#` `ppp`

and then `dial provider` to start the PPP session, or, if you want `ppp` to establish sessions automatically when there is outbound traffic (and you have not created the `start_if.tun0` script), type:

`#` `ppp -auto provider`

#### 25.2.1.6. Summary

To recap, the following steps are necessary when setting up ppp for the first time:

Client side:

1. Ensure that the `tun` device is built into your kernel.

2. Ensure that the `tun`N`` device file is available in the `/dev` directory.

3. Create an entry in `/etc/ppp/ppp.conf`. The `pmdemand` example should suffice for most ISPs.

4. If you have a dynamic IP address, create an entry in `/etc/ppp/ppp.linkup`.

5. Update your `/etc/rc.conf` file.

6. Create a `start_if.tun0` script if you require demand dialing.

Server side:

1. Ensure that the `tun` device is built into your kernel.

2. Ensure that the `tun`N`` device file is available in the `/dev` directory.

3. Create an entry in `/etc/passwd` (using the vipw(8) program).

4. Create a profile in this users home directory that runs `ppp -direct direct-server` or similar.

5. Create an entry in `/etc/ppp/ppp.conf`. The `direct-server` example should suffice.

6. Create an entry in `/etc/ppp/ppp.linkup`.

7. Update your `/etc/rc.conf` file.

前一頁 | 上一層 | 下一頁
章 25. PPP and SLIP | 起始頁 | 25.3. Using Kernel PPP

本文及其他文件，可由此下載： ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/。

若有 FreeBSD 方面疑問，請先閱讀 FreeBSD 相關文件，如不能解決的話，再洽詢 <questions@FreeBSD.org>。
關於本文件的問題，請洽詢 <doc@FreeBSD.org>。