章 27. PPP

In order to configure a PPP connection, first edit /etc/ppp/ppp.conf with the dial-in information for the ISP. This file is described as follows:

Depending upon whether ppp(8) is started manually or automatically, a /etc/ppp/ppp.linkup may also need to be created which contains the following lines. This file is required when running ppp in -auto mode. This file is used after the connection has been established. At this point, the IP address will have been assigned and it is now be possible to add the routing table entries. When creating this file, make sure that provider matches the value demonstrated in line 11 of ppp.conf.

This file is also needed when the default gateway address is "guessed" in a static IP address configuration. In this case, remove line 17 from ppp.conf and create /etc/ppp/ppp.linkup with the above two lines. More examples for this file can be found in /usr/shared/examples/ppp/.

By default, ppp must be run as root. To change this default, add the account of the user who should run ppp to the network group in /etc/group.

Then, give the user access to one or more entries in /etc/ppp/ppp.conf with allow. For example, to give fred and mary permission to only the provider: entry, add this line to the provider: section:

To give the specified users access to all entries, put that line in the default section instead.

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.

And for PPP version 2 and above:

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.

While ppp is now configured, some edits still need to be made to /etc/rc.conf.

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

If the ISP has supplied a static IP address and name, use this name as the host name.

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

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

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 a good idea to ensure 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:

The downside is that sendmail is forced to re-examine the mail queue whenever the ppp link. To automate this, include !bg in ppp.linkup:

An alternative is 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, either type:

and then dial provider to start the PPP session, or, to configure ppp to establish sessions automatically when there is outbound traffic and start_if.tun0 does not exist, type:

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 the configuration:

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.

撥入服務 provides a good description on enabling dial-up services using getty(8).

An alternative to getty is comms/mgetty+sendfax port), 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 the modem will not answer the phone.

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

Refer to http://mgetty.greenie.net/doc/mgetty_toc.html for more information on mgetty.

By default the comms/mgetty+sendfax port comes with the AUTO_PPP option enabled allowing 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 compiled, and installed the comms/mgetty+sendfax port on his system.

Ensure that /usr/local/etc/mgetty+sendfax/login.config has the following:

This tells mgetty to run ppp-pap-dialup for detected PPP connections.

Create an executable file called /etc/ppp/ppp-pap-dialup containing the following:

For each dial-up 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.

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

To assign some users a static IP number, specify the number as the third argument in /etc/ppp/ppp.secret. See /usr/shared/examples/ppp/ppp.secret.sample for examples.

When using a custom kernel, make sure to include the following line in the kernel configuration file:

The uart device is already included in the GENERIC kernel, so no additional steps are necessary in this case. Just check the dmesg output for the modem device with:

This should display some pertinent output about the uart devices. These are the COM ports we need. If the modem acts like a standard serial port, it should be listed on uart1, or COM2. If so, a kernel rebuild is not required. When matching up, if the modem is on uart1, the modem device would be /dev/cuau1.

Connecting to the Internet by manually controlling ppp is quick, easy, and a great way to debug a connection or just get information on how the ISP treats ppp client connections. Lets start PPP from the command line. Note that in all of our examples we will use example as the hostname of the machine running PPP. To start ppp:

This second command sets the modem device to cuau1.

This sets the connection speed to 115,200 kbps.

This tells ppp to configure the resolver and add the nameserver lines to /etc/resolv.conf. If ppp cannot determine the hostname, it can manually be set later.

This switches to "terminal" mode in order to manually control the modem.

Use at to initialize the modem, then use atdt and the number for the ISP to begin the dial in process.

Confirmation of the connection, if we are going to have any connection problems, unrelated to hardware, here is where we will attempt to resolve them.

At this prompt, return the prompt with the username that was provided by the ISP.

At this prompt, reply with the password that was provided by the ISP. Just like logging into FreeBSD, the password will not echo.

Depending on the ISP, this prompt might not appear. If it does, it is asking whether to use a shell on the provider or to start ppp. In this example, ppp was selected in order to establish an Internet connection.

Notice that in this example the first p has been capitalized. This shows that we have successfully connected to the ISP.

We have successfully authenticated with our ISP and are waiting for the assigned IP address.

We have made an agreement on an IP address and successfully completed our connection.

Here we add our default route, we need to do this before we can talk to the outside world as currently the only established connection is with the peer. If this fails due to existing routes, put a bang character ! in front of the add. Alternatively, set this before making the actual connection and it will negotiate a new route accordingly.

If everything went good we should now have an active connection to the Internet, which could be thrown into the background using CTRL+z If PPP returns to ppp then the connection has bee lost. This is good to know because it shows the connection status. Capital P’s represent a connection to the ISP and lowercase p’s show that the connection has been lost.

If a connection cannot be established, turn hardware flow CTS/RTS to off using set ctsrts off. This is mainly the case when connected to some PPP-capable terminal servers, where PPP hangs when it tries to write data to the communication link, and waits for a Clear To Send (CTS) signal which may never come. When using this option, include set accmap as it may be required to defeat hardware dependent on passing certain characters from end to end, most of the time XON/XOFF. Refer to ppp(8) for more information on this option and how it is used.

An older modem may need set parity even. Parity is set at none be default, but is used for error checking with a large increase in traffic, on older modems.

PPP may not return to the command mode, which is usually a negotiation error where the ISP is waiting for negotiating to begin. At this point, using ~p will force ppp to start sending the configuration information.

If a login prompt never appears, PAP or CHAP authentication is most likely required. To use PAP or CHAP, add the following options to PPP before going into terminal mode:

Where myusername should be replaced with the username that was assigned by the ISP.

Where mypassword should be replaced with the password that was assigned by the ISP.

If a connection is established, but cannot seem to find any domain name, try to ping(8) an IP address. If there is 100 percent (100%) packet loss, it is likely that a default route was not assigned. Double check that add default HISADDR was set during the connection. If a connection can be made to a remote IP address, it is possible that a resolver address has not been added to /etc/resolv.conf. This file should look like:

Where x.x.x.x and y.y.y.y should be replaced with the IP address of the ISP’s DNS servers.

To configure syslog(3) to provide logging for the PPP connection, make sure this line exists in /etc/syslog.conf:

有時需要使用服務標籤 (Service Tag) 才能建立連線，服務標籤用來區別不同網路要各自連線的 PPPoE 伺服器。

所需的服務標籤資訊應該會在 ISP 所提供的文件中說明。

最後的手段是嘗試安裝 net/rr-pppoe 套件或 Port。但是請注意，這可能會解除安裝數據機中的程式並使其無法運作，所以請三思而為。只需要安裝數據機所提供的程式，然後由該程式進入 System 選單，基本資料 (Profile name) 的名稱應該會列出來，通常是 ISP 的名稱。

基本資料名稱 (Profile Name) 即服務標籤，會被用在 ppp.conf 中的 PPPoE 設定項目，set device 的提供商 (Provider) 部份。請參考 ppp(8) 以取得詳細說明，結果應如下：

別忘記更改 xl1 為乙太網路卡的裝置名稱。

別忘記更改 ISP 為基本資料名稱。

要取得更進一步資訊，請參考 Renaud Waldura 所著的 Cheaper Broadband with FreeBSD on DSL。

這台數據機並不採用 RFC 2516 所定義的規格。

為了要讓 FreeBSD 能夠與這台裝置通訊，必須設定 sysctl，這可以透過更新 /etc/sysctl.conf 來讓開機時自動設定。

或可以執行以下指令立即更改：

不幸的是，由於這是一個全系統的設定，這可能導致一般 PPPoE 客戶端或伺服器無法與 3Com™HomeConnect™ ADSL 數據機同時使用。

The mpd application can be used to connect to a variety of services, in particular PPTP services. It can be installed using the net/mpd5 package or port. Many ADSL modems require that a PPTP tunnel is created between the modem and computer.

Once installed, configure mpd to suit the provider’s settings. The port places a set of sample configuration files which are well documented in /usr/local/etc/mpd/. A complete guide to configure mpd is available in HTML format in /usr/ports/shared/doc/mpd/. Here is a sample configuration for connecting to an ADSL service with mpd. The configuration is spread over two files, first the mpd.conf:

Information about the link, or links, to establish is found in mpd.links. An example mpd.links to accompany the above example is given beneath:

It is possible to initialize the connection easily by issuing the following command as root:

To view the status of the connection:

Using mpd is the recommended way to connect to an ADSL service with FreeBSD.

It is also possible to use FreeBSD to connect to other PPPoA services using net/pptpclient.

To use net/pptpclient to connect to a DSL service, install the port or package, then edit /etc/ppp/ppp.conf. An example section of ppp.conf is given below. For further information on ppp.conf options consult ppp(8).

This will open a tunnel for a PPP session to the DSL router. Ethernet DSL modems have a preconfigured LAN IP address to connect to. In the case of the Alcatel SpeedTouch™ Home, this address is 10.0.0.138. The router’s documentation should list the address the device uses. To open the tunnel and start a PPP session:

A tun virtual tunnel device will be created for interaction between the pptp and ppp processes. Once the prompt is returned, or the pptp process has confirmed a connection, examine the tunnel:

If the connection fails, check the configuration of the router, which is usually accessible using a web browser. Also, examine the output of pptp and the contents of the log file, /var/log/ppp.log for clues.