The Care and Feeding of ISDN4BSD
10.4.1 ISDN Problems	10.4 Troubleshooting the PPP	10.4.3 Using tcpdump

10.4.2 sppp Problems

Problems with the sppp module can be debugged by tracing its actions. Trace output will be enabled by adding the debug flag to the final ifconfig command like this:

ifconfig isp0 0.0.0.0 192.76.124.10 netmask 0xffffffff link1 debug

When you then issue the command ifconfig isp0, you'll notice

<ROOT@hmpc>/root ifconfig isp0

isp0: flags=2815<UP,DEBUG,POINTOPOINT,SIMPLEX,LINK1> mtu 1500

inet 0.0.0.0 -> 192.76.124.10 netmask 0xffffffff

that the DEBUG flag is now switched on. If you now execute the telnet command to the remote side, you'll see an output similar to the following appearing either on the console or in /var/log/messages or on both:

isp0: lcp open(initial)

isp0: phase establish

isp0: Up event

isp0: lcp up(starting)

isp0: lcp output <conf-req id=0x1d len=10 05-06-66-27-2d-20>

isp0: lcp input(req-sent): <conf-req id=0x4b len=15 03-05-c2-23-05-05-06-6e-e8-f4-e0>

isp0: lcp parse opts:  auth-proto  magic

isp0: lcp parse opt values:  auth-proto  magic 0x6ee8f4e0  send conf-ack

isp0: lcp output <conf-ack id=0x4b len=15 03-05-c2-23-05-05-06-6e-e8-f4-e0>

isp0: lcp input(ack-sent): <conf-ack id=0x1d len=10 05-06-66-27-2d-20>

isp0: lcp tlu

isp0: phase authenticate

isp0: chap input <challenge id=0x33 len=26 name=c_xxx value-size=16

value= 6e-e8-f4-e9-58-53-1f-0f-04-b3-a3-fc-c3-7b-cc-f4>

isp0: chap output <response id=0x33 len=26

10-34-eb-bd-71-55-56-5d-c1-15-86-2f-d5-c9-fa-ae-90-68-6d-62-73-64>

isp0: chap success

isp0: phase network

isp0: ipcp open(initial)

isp0: ipcp up(starting)

isp0: ipcp output <conf-req id=0x1e len=10 03-06-00-00-00-00>

isp0: ipcp input(req-sent): <conf-req id=0x33 len=10 03-06-c0-4c-7c-0a>

isp0: ipcp parse opts:  address

isp0: ipcp parse opt values:  address [wantmyaddr 192.76.124.10] [agree]  send conf-ack

isp0: ipcp output <conf-ack id=0x33 len=10 03-06-c0-4c-7c-0a>

isp0: lcp output <proto-rej id=0x1f len=10 82-07-01-33-00-04>

isp0: invalid input protocol <addr=0xff ctrl=0x3 proto=0x8207>

isp0: ipcp input(ack-sent): <conf-nak id=0x1e len=10 03-06-c0-a8-a8-a8>

isp0: ipcp nak opts:  address [wantaddr 192.168.168.168] [agree]

isp0: ipcp output <conf-req id=0x20 len=10 03-06-c0-a8-a8-a8>

isp0: ipcp input(ack-sent): <conf-ack id=0x20 len=10 03-06-c0-a8-a8-a8>

isp0: ipcp tlu

isp0: lcp input(opened): <echo-req id=0x1 len=12 6e-e8-f4-e0-00-60-70-62>

isp0: got lcp echo req, sending echo rep

isp0: lcp output <echo-reply id=0x1 len=12 66-27-2d-20-00-60-70-62>