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System Administration Guide: Network Services
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Tools for Troubleshooting PPP

PPP links generally have three major areas of failure:

  • Failure of the link to be established

  • Poor performance of the link during regular usage

  • Problems that can be traced to the networks on either side of the link

The easiest way to find out if PPP works is to run a command over the link. Run a command such as ping or traceroute to a host on the peer's network. Then observe the results. However, you should use PPP and UNIX debugging tools to monitor performance of an established link or to troubleshoot a problematic link.

This section explains how to obtain diagnostic information from pppd and its associated log files. The remaining sections in this chapter describe common problems with PPP that you can discover and fix with the aid of the PPP troubleshooting tools.

How to Obtain Diagnostic Information From pppd

The next procedure shows how to view the current operation of a link on the local machine.

  1. Become superuser on the local machine or assume an equivalent role.

    Roles contain authorizations and privileged commands. For more information about roles, see Configuring RBAC (Task Map) in System Administration Guide: Security Services. To configure a role with the Primary Administrator profile, see Chapter 2, Working With the Solaris Management Console (Tasks), in System Administration Guide: Basic Administration.

  2. Run pppd with the serial device configured for PPP as the argument:
    # pppd cua/b debug updetach

    The next examples show the resulting displays for a dial-up link and a leased-line link when pppd runs in the foreground. If you run pppd debug in the background, the output that is produced is sent to the /etc/ppp/connect-errors file.

Example 21-1 Output From a Properly Operating Dial-up Link
# pppd /dev/cua/b debug updetach
have route to 0.0.0.0/0.0.0.0 via 172.21.0.4
serial speed set to 230400 bps
Using interface sppp0
Connect: sppp0 <--> /dev/cua/b
sent [LCP ConfReq id=0x7b <asyncmap 0x0> <magic 0x73e981c8> <pcomp> <accomp>]
rcvd [LCP Ident id=0x79 magic=0x0 "ppp-2.4.0b1 (Sun Microsystems, Inc., Oct  6 
    2004 09:36:22)"]
Peer Identification: ppp-2.4.0b1 (Sun Microsystems, Inc., Oct  6 2004 09:36:22)
    rcvd [LCP ConfRej id=0x7b <asyncmap 0x0>]
sent [LCP Ident id=0x7c magic=0x0 "ppp-2.4.0b1 (Sun Microsystems, Inc., Sep 15 
    2004 09:38:33)"
sent [LCP ConfReq id=0x7d <magic 0x73e981c8> <pcomp> <accomp>]
rcvd [LCP ConfAck id=0x7d <magic 0x73e981c8> <pcomp> <accomp>]
rcvd [LCP ConfAck id=0x78 <magic 0xdd4ad820> <pcomp> <accomp>]
sent [LCP ConfAck id=0x78 <magic 0xdd4ad820> <pcomp> <accomp>]
sent [LCP Ident id=0x7e magic=0x73e981c8 "ppp-2.4.0b1 (Sun Microsystems, Inc., 
    Sep 15 2004 09:38:33)"]
sent [IPCP ConfReq id=0x3d <addr 0.0.0.0> <compress VJ 0f 01>]
rcvd [LCP Ident id=0x7a magic=0xdd4ad820 "ppp-2.4.0b1 (Sun Microsystems, Inc., 
    Oct  6 2004 09:36:22)"]
Peer Identification: ppp-2.4.0b1 (Sun Microsystems, Inc., Oct  6 2004 09:36:22)
rcvd [IPCP ConfReq id=0x92 <addr 10.0.0.1> <compress VJ 0f 01>
sent [IPCP ConfAck id=0x92 <addr 10.0.0.1> <compress VJ 0f 01>
rcvd [IPCP ConfNak id=0x3d <addr 10.0.0.2>]]
sent [IPCP ConfReq id=0x3e <addr 10.0.0.2> <compress VJ 0f 01>]
rcvd [IPCP ConfAck id=0x3e <addr 10.0.0.2> <compress VJ 0f 01>]
local  IP address 10.0.0.2
remote IP address 10.0.0.1
Example 21-2 Output From a Properly Operating Leased-Line Link
# pppd /dev/se_hdlc1 default-asyncmap debug updetach
pppd 2.4.0b1 (Sun Microsystems, Inc., Oct 24 2004 07:13:18) started by root, uid 0
synchronous speed appears to be 0 bps
init option: '/etc/ppp/peers/syncinit.sh' started (pid 105122)
Serial port initialized.
synchronous speed appears to be 64000 bps
Using interface sppp0
Connect: sppp0 <--> /dev/se_hdlc1
sent [LCP ConfReq id=0xe9 <magic 0x474283c6><pcomp> <accomp>]
rcvd [LCP ConfAck id=0xe9 <magic 0x474283c6><pcomp> <accomp>]
rcvd [LCP ConfReq id=0x22 <magic 0x8e3a53ff><pcomp> <accomp>]
sent [LCP ConfReq id=0x22 <magic 0x8e3a53ff><pcomp> <accomp>]
sent [LCP Ident id=0xea magic=0x474283c6 "ppp-2.4.0b1 (Sun Microsystems, Inc., Oct 
    22 2004 14:31:44)"]
sent [IPCP ConfReq id=0xf7 <addr 0.0.0.0> <compress VJ Of o1>]]
sent [CCP ConfReq id=0x3f <deflate 15> <deflate(old#) 15> <bsd v1 15>]
rcvd [LCP Ident id=0x23 magic=0x8e3a53ff "ppp-2.4.0b1 (Sun Microsystems, Inc., Oct 
    22 2004 14:31:44)"]
Peer Identification: ppp-2.4.0b1 (Sun Microsystems, Inc., Oct 22 2004 14:31:44)
rcvd [IPCP ConfReq id=0x25 <addr 10.0.0.1> <compress VJ Of 01>]
sent [IPCP ConfAck id=0x25 <addr 10.0.0.1> <compress VJ Of 01>]
rcvd [CCP ConfReq id=0x3 <deflate 15> <deflate(old#) 15 <bsd v1 15>]
sent [CCP ConfAck id=0x3 <deflate 15> <deflate(old#) 15 <bsd v1 15>]
rcvd [IPCP ConfNak id=0xf8 <addr 10.0.0.2>]
rcvd [IPCP ConfReq id=0xf7 <addr 10.0.0.2> <compress VJ Of 01>]
rcvd [CCP ConfAck id=0x3f <deflate 15> <deflate(old#) 15 <bsd v1 15>]
Deflate (15) compression enabled
rcvd [IPCP ConfAck id=0xf8 <addr 10.0.0.2> <compress VJ Of 01>]
local  IP address 10.0.0.2
remote IP address 10.0.0.1

How to Turn on PPP Debugging

The next task shows how to use the pppd command to obtain debugging information.


Note - You only need to perform step 1 through step 3 once for each host. Thereafter, you can proceed to step 4 to turn on debugging for the host.


  1. Become superuser or assume an equivalent role.

    Roles contain authorizations and privileged commands. For more information about roles, see Configuring RBAC (Task Map) in System Administration Guide: Security Services. To configure a role with the Primary Administrator profile, see Chapter 2, Working With the Solaris Management Console (Tasks), in System Administration Guide: Basic Administration.

  2. Create a log file to hold output from pppd.
    # touch /var/log/pppdebug
  3. Add the following syslog facilities for pppd in /etc/syslog.conf.
    daemon.debug;local2.debug /var/log/pppdebug
  4. Restart syslogd.
    # pkill -HUP -x syslogd
  5. Turn on debugging for calls to a particular peer by using the following syntax of pppd.
    # pppd debug call peer-name 

    peer-name must be the name of a file in the /etc/ppp/peers directory.

  6. View the contents of the log file.
    # tail -f /var/log/pppdebug

    For an example of a log file, see Step 3.

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