Re: remote IP address not being sent

In article <1122476172.273100.17490@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
<js2k2000@xxxxxxxxx> wrote:
>I/m trying to debug some software that uses a PPP client in an embedded
>device. The ISP PPP server that it connects to never sends a
>configuration-request with an IP-address field, so the client never
>learns the remote IP address.

Why do you care? As long as you have an IP address for yourself,
the IP address of the machine you're connected to is of little use.

>When I connect from a WinXP PC using the Microsoft supplied PPP client
>the ISP does send a configuration-request with an IP-address field.

Same ISP?

>Anyone know what would cause this?
>
>This is the PPP sequence, Note that SENDING is from the Clients
>perspective.
>
>SENDING
>C0 21
>01 01 CONF_REQ #1
>00 18
>08 02 ACFC
>07 02 PFC
>05 06 0E B9 2D A9 magic #
>02 06 00 00 00 00 ACCM = 0x00000000
>01 04 05 DC
>
>RECEIVED
>C0 21
>01 01 CONF_REQ #1
>00 1C
>01 04 05 DC max
>02 06 00 0A 00 00 ACCM = 0x000a0000
>03 04 C0 23 authen = PAP
>05 06 3C 5E 8D DD magic
>07 02 comp
>08 02 comp
>6E B0 (crc)
>
>SENDING
>C0 21
>02 01 ACK #1
>00 1C
>01 04 05 DC
>02 06 00 0A 00 00 COMP IP
>03 04 C0 23
>05 06 3C 5E 8D DD
>07 02
>08 02
>
>RECEIVED NB
>C0 21
>02 01 ACK #1
>00 18
>08 02
>07 02
>05 06 0E B9 2D A9 COMP IP
>02 06 00 00 00 00
>01 04 05 DC
>8D 4D (crc)

Pretty normal so far...

>----------- authentication ------
>SENDING
>C0 23 PAP REQ
>01 02
>00 0C
>03 75 64 6E
>03 75 64 6E
>
>
>RECEIVED
>C0 23 PAP_CODE_AUTH_ACK
>02 02
>00 05
>00
>30 15 (crc)

Looks good...

>------------ end authen ----------------------
>SENDING
>80 21 IP
>01 01 REQ #1
>00 22
>03 06 00 00 00 00 IP address
>81 06 00 00 00 00
>82 06 00 00 00 00
>83 06 00 00 00 00
>84 06 00 00 00 00
>
>
>RECEIVED
>80 21 IP
>01 01 REQ #1
>00 0A
>02 06 00 2D 0F 00 COMP IP

This is where your peer would have first sent you its IP address
if it wanted you to know it.

>SENDING
>80 21 IP
>04 01 REJ #1
>00 0A
>02 06 00 2D 0F 00 comp IP

Your machine tells the peer you don't want any IP header compression.

> <<--- this is where I would have expected the remote ip addess.
>
>RECEIVED
>80 21 IP
>04 01 REJ #1
>00 10
>82 06 00 00 00 00
>84 06 00 00 00 00
>9D EA (crc)

The peer tells you it doesn't do NBNS servers.

>SENDING NB
>80 21 IP
>01 02 REQ #2
>00 16
>03 06 00 00 00 00 IP address
>81 06 00 00 00 00
>83 06 00 00 00 00

Your machine asks for an IP address and some DNS server addresses.

>RECEIVED
>80 FD compression proto
>01 01 REQ #1
>00 0A
>12 06 00 00 00 01
>DB 5D

The peer asks to do link level compression.

>SENDING
>C0 21
>08 01 protocol reject #1
>00 12
>80 FD the one above
>01 01
>00 0A 12 06 00 00 00 01 DB 5D

Your machine says it doesn't want to do any link level compression.

(FYI - you don't have to (you're not supposed to) include the
rejected frame's CRC)

>RECEIVED
>80 21 IP
>01 02 req #2
>00 04
>DF 76 (crc)

The peer negotiates IP with no options.

>SENDING
>80 21 IP
>02 02 ACK #2
>00 04

Your machine says it's OK with that.

>RECEIVED
>80 21 IP
>03 02 NAK #2
>00 16
>03 06 3D 1E 40 31 IP addr
>81 06 3D 1F E9 01
>83 06 D3 4E D7 C8
>B4 EC

The peer tells you want your IP address and DNS addresses should be.

>SENDING
>80 21 IP
>01 03 REQ #2
>00 16
>03 06 3D 1E 40 31 ip address
>81 06 3D 1F E9 01
>83 06 D3 4E D7 C8

Your machine asks for that IP address and those DNS addresses.

>RECEIVED
>80 21 IP
>02 03 ACK #3
>00 16
>03 06 3D 1E 40 31 IP address
>81 06 3D 1F E9 01
>83 06 D3 4E D7 C8
>85 72

The peer accepts your IP address and DNS addresses.

>Negotiated local IP: 3D1E4031,
>remote IP: 00000000,
>DNS1 IP: 3D1FE901,
>DNS2 IP: D34ED7C8

You have your local IP address. Why do you care what the remote's IP
address is?

You'd really need a complete dump of the WinXP client dialing into your
ISP to see what might make the ISP offer it's IP address during IPCP.

Patrick
=========== For PPP Protocol Analysis, check out PacketView Pro! ===========
Patrick Klos Email: patrick@xxxxxxxx
Klos Technologies, Inc. Web: http://www.klos.com/
=========== "www" stands for Wild Wild West, NOT World Wide Web! ===========

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