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Everything you could possibly want to know about the technical whys and becauses is in the official definition, RFC 2516. However, here's the meat of this protocol and how it works:

PPP
PPP is an acronym for Point to Point Protocol.
PPP is a member of the TCP/IP suite of network protocols.
PPP is an extension to TCP/IP that adds user ID and password security.
LCP is an acronym for Link Control Protocol and is a component of PPP.
IPCP is an acronym for IP Control Protocol and is a component of PPP.

PPPoE
PPPoE is an acronym for Point to Point Protocol over Ethernet PPP, which was designed for serial communications, has been combined with Ethernet, and is appropriately known as PPPoE. PPP was designed to do things that were either impossible or unnecessary with Ethernet, users are often confused as to why one would want to use PPP over Ethernet at all. The use of PPPoE, which allows ISP's and CLEC's to secure communications through the use of user ID's and passwords and have the ability to measure/monitor the traffic of each user. Some DSL providers don't use PPPoE.

PPPoE is a standard, and you may think that all PPPoE clients are equal. As in most things, some are more equal than others. The standard requires that PPPoE clients add an additional header to the beginning of each TCP/IP packet. This may cause the packet to become larger than the maximum allowable size. Some PPPoE client solutions handle this transparently, but some require you to modify the TCP/IP settings on all of the client computers on the LAN.

Some modem's show some of the exchange other's show it all. There are RFC's for all mentioned Protocols refer to them to understand the information given.

Below is a very detailed PPPoE exchange from start to finish:

00:00:23 POE: Sending PADI packet for PPP
00:00:23 POE: ENET Received PADO packet
00:00:23 POE: Sending PADR packet for PPP
00:00:23 POE: ENET Received PADS packet
00:00:23 POE: PPP Session ID = 0x1e12 is open
00:00:23 PPP: LCP We processed peer's requests:
00:00:23 PPP: max-recv-unit, mru 1492 (ack)
00:00:23 PPP: auth-type, auth (ack)
00:00:23 PPP: magic-num, 0x41d8799 (ack)
00:00:23 PPP: LCP Peer acknowledged our requests:
00:00:23 PPP: mru 1492
00:00:23 PPP: magic-num, 0xea27fe02
00:00:23 PPP: LCP We processed peer's requests:
00:00:23 PPP: max-recv-unit, mru 1492 (ack)
00:00:23 PPP: auth-type, auth (ack)
00:00:23 PPP: magic-num, 0xdeeb76cb (ack)
00:00:23 PPP: LCP Peer acknowledged our requests:
00:00:23 PPP: mru 1492
00:00:23 PPP: magic-num, 0xb9aebba6
00:00:23 PPP: PAP authentication success reported by peer
00:00:23 IPCP: Resettings options: ip (0.0.0.0), dns (0.0.0.0, 0.0.0.0)
00:00:23 IPCP: IPCP We acknowledged peer's requests:
00:00:23 IPCP: IP-Addr: peer-addr 216.117.66.1
00:00:23 IPCP: Peer Nak'd our addr (0.0.0.0) with addr (216.117.108.2); accepting peer's address preference
00:00:23 IPCP: Peer Nak'd our primary DNS (0.0.0.0) with (209.172.192.2); accepting peer's primary DNS address
00:00:23 IPCP: Peer Nak'd our secondary DNS (0.0.0.0) with (209.172.194.2); accepting peer's secondary DNS address
00:00:23 IPCP: IPCP Peer acknowledged our request:
00:00:23 IPCP: IP-Addr: local-addr 216.117.108.2
00:00:23 IPCP: Primary DNS: 209.172.192.2
00:00:23 IPCP: Secondary DNS: 209.172.194.2
00:00:23 IPCP: IP up, local 216.117.108.2, remote 216.117.66.1


This is a breakdown/explaination of a 5100b modem log posted by core network See Profile with edits it may give some insight to what is going on with the PPPoE exchange.
NOTE: The 5100b modem log has a time delay for its entries.

2004/05/06 00:56:13 GMT E |System |=========== SYSTEM UP ===========
2004/05/06 00:56:13 GMT E |System |Current Mode: PPP on the modem (Public IP for LAN device)
2004/05/06 00:56:14 GMT E |DSL |DataPump Version 01.01.00.00
2004/05/06 00:56:14 GMT E |DSL |State: WAITING
Modem has finished booting up

2004/05/06 00:56:15 GMT E |Ethernet |Link 1 Up - 100Base-TX Full Duplex
Ethernet port is up

2004/05/06 00:56:16 GMT E |DSL |State: INITIALIZING
2004/05/06 00:56:28 GMT E |DSL |State: WAITING
2004/05/06 00:56:30 GMT E |DSL |State: INITIALIZING
Modem is doing its Synchronization routine

2004/05/06 00:56:43 GMT E |DSL |HYBRID 2
This line can also end with HYBRID 3

2004/05/06 00:56:38 GMT E |DSL |Link up 1 US 160 DS 1536 (FAST:G.dmt)
you know what this step is - your negotiated speed with the DSLAM port itself.
00:56:38 GMT=Time Stamp GMTin EST this would be 7:56:38pm/19:56:38
E |DSL=Section of modem making this entry
Link up 1=Number of times modem has achieved synchronization a reboot will reset counter to 0
US 160 DS 1536=Sync rates
(FAST:G.dmt)=Fastpath/Interleaved Explanation
(FAST:G.dmt)=Encoding standard TI.413 is also used

2004/05/06 00:56:46 GMT E |PPPoE |tx PADI, id: 0000, ac: (NULL), sn: (NULL)
Here your modem/router is trying to initiate a PPPOE session. The PADI is the first step in a 4-way handshake that the PPPOE protocol uses for session establishment.
tx=Transmit

2004/05/06 00:56:46 GMT E |PPPoE |rx AC Name: 62031020042800-ipltinho03w
This is step number 2. The name here that you are seeing is actually the name of the ASI RedBack router. This is because your PPPOE session is actually being handled by ASI, not the ISP. The name of this packet being sent back to you is PADO. ASIs router is actually offering to act as the PPPOE server. This router is usually transparent to the end user, but it can be seen when looking at the output from a PPPoE client. It's also visible in the system properties section of the Enternet 300 software client.
rx=Recieve
AC Name=Access Concentrator/RedBack router

2004/05/06 00:56:46 GMT E |PPPoE |tx PADR, id: 0000, ac: (NULL), sn:
3. In this step your router/PPPOE client has received the PADO packet from ASIs router, and is requesting sending a PADR to establish a PPPOE session with this router, much the same way a NIC card will establish an IP address from a DHCP server.

2004/05/06 00:56:46 GMT E |PPPoE |rx PADS id: 2BAF
After you send the PADR packet, then the last step of the PPPOE 4-way handshake is complete, the PADS packet that is sent back to you. Think of this as the PAD Standby while I authenticate your session with the ISP. This is because the ASI router does your ppp authentication for you this is known as proxy ppp. You have already sent me your login and password info by step 3.
id: 2BAF=This is the Session ID

2004/05/06 00:56:46 GMT E |PPP |LCP neg PAP
The beginning of the ppp authentication process
LCP=Link Control Protocol
PAP=Password Authentication Protocol

2004/05/06 00:56:46 GMT E |PPP |LCP up
You login credentials have been received and approved. You are halfway there at this point.

2004/05/06 00:56:48 GMT E |PPP |IPCP nak option: 3
The NCP phase of ppp, or Network Control Protocol, has begun. Right now you are being told to standby for DNS info coming your way.

2004/05/06 00:56:48 GMT E |PPP |IPCP nak option: 129
This is an acknowledgement of the first DNS server address you have received.

2004/05/06 00:56:48 GMT E |PPP |IPCP nak option: 131
This is an acknowledgement of the second DNS server address you have received.

2004/05/06 00:56:48 GMT E |PPP |IPCP up ip: 68.251.190.179, gw: 68.251.191.254, dns: 67.36.128.26, 206.141.192.60
This should be obvious. Your IP address,gateway and DNS info have now been assigned.

2004/05/06 00:56:57 GMT E |SNTP Client |Updated time from Primary server 132.163.4.103
A timestamp of when your session began.
SNTP Client=Simple Network Time Protocol
Two public time servers are used to set and update the modems clock
From this point on it should be happy trails - you are free to roam the beautiful world we call "internet". Have fun and watch out for infections.

2004/03/18 10:57:25 GMT E |DSL |Link Down
2004/03/18 10:57:25 GMT E |DSL |State: WAITING
2004/03/18 10:57:31 GMT E |DSL |State: INITIALIZING
2004/03/18 10:57:39 GMT E |DSL |HYBRID 2
2004/03/18 10:57:39 GMT E |DSL |Link up 8 US 160 DS 1536 (FAST:G.dmt)
2004/03/18 20:15:41 GMT E |DSL |Link Down
2004/03/18 20:15:41 GMT E |DSL |State: WAITING
2004/03/18 20:15:44 GMT E |DSL |State: INITIALIZING
2004/03/18 20:15:52 GMT E |DSL |HYBRID 2
2004/03/18 20:15:52 GMT E |DSL |Link up 9 US 160 DS 1536 (FAST:G.dmt)
2004/03/18 20:18:00 GMT E |DSL |Link Down
2004/03/18 20:18:00 GMT E |DSL |State: WAITING
2004/03/18 20:18:07 GMT E |DSL |State: INITIALIZING
2004/03/18 20:18:15 GMT E |DSL |HYBRID 2
2004/03/18 20:18:15 GMT E |DSL |Link up 10 US 160 DS 1536 (FAST:G.dmt)
The section above shows sync loss three times but the PPP session (IP) does not go down

2004/03/21 09:31:17 GMT E |PPP |Max echo misses
2004/03/21 09:31:17 GMT E |PPP |LCP down
2004/03/21 09:31:17 GMT E |PPP |IPCP down
2004/03/21 09:31:35 GMT E |PPPoE |tx PADT, id:28AA, ac:(NULL), sn:(NULL)
The section above shows the PPP session being Terminated by the modem in response to the Max echo misses by sending a PADT , the PPP session can also be terminated by the Access Concentrator/RedBack router if it sends a PADT or a loss of sync

Expand got feedback?

by wayjac See Profile edited by lev See Profile
last modified: 2004-05-30 22:05:41