PPPoE & PPP

PPPoE

• PPPoE：Point-to-Point Protocol over Ethernet，RFC 2516；
• PPP：Point-to-Point Protocol，RFC 1661；
• For encapsulating PPP frames inside Ethernet frames.
  
  

  PPPoE and TCP/IP protocol stack

Typical PPP over Ethernet Topology

• PPPoE 的两个阶段：PPPoE Discovery，PPP session

• PPPoE Discovery
  Client to server: Initiation
  Server to client: Offer
  Client to server: request
  Server to client: session-confirmation

• PPP session
  Either end to other end: termination.

• EtherType；
  The ETHER_TYPE is set to either 0x8863 (Discovery Stage) or 0x8864 (PPP Session Stage).
  

  

  Ethernet II

• 1492？！
  The MRU (Maximum-Receive-Unit) option MUST NOT be negotiated to a larger size than 1492. Since Ethernet has a maximum payload size of 1500 octets, the PPPoE header is 6 octets and the PPP Protocol ID is 2 octets, the PPP MTU MUST NOT be greater than 1492.

• Ethernet payload
  PPPoE Discovery phase and PPPoE PPP session phase packets travel as payload in an Ethernet frame. The Ethernet payload for PPPoE always start with a VERSION field, TYPE field, CODE field, SESSION ID and LENGTH as shown below.
  

  

  Ethernet frame with payload

Ethernet payload for PPPoE

• PPPoE Header

  
  
  

  PPPoE header fields (6 bytes)

• PPPoE Payload

  
  
  

  PPPoE Payload

• Treck wiki 上的 PPP over Ethernet (PPPoE) Interface 可以读一下。

DSL Internet access architecture

DSL Internet access architecture

PPP

• PPP 是 data link layer (layer 2) 数据链路层协议。

  
  
  

  PPP three main components: Encapsulation, LCP, NCP
• How does PPP create a link and communicate between two machines?
  Communication is established in essentially three phases:
  1. Link Control Protocol (LCP)
  2. Authentication
  3. Network Control Protocol (NCP)

PPP architecture

Internet protocol suite

• PPP Encapsulation
  

  

  PPPoE Payload

• RFC 1662 (PPP in HDLC-like Framing)
  

  

  PPP General Frame Format(RFC 1662)

• PPP General Frame Format (HDLC-like)

Linux 拨号

• RP-PPPoE
  Roaring Penguin 公司提供的免费版 PPPoE client for Linux and Solaris systems to connect to PPPoE service providers.
  yum install rp-pppoe 可以安装。
• 当前最新版 rp-pppoe-3.12.tar.gz；
  可以查看 doc 和 man 下文件了解。
• -I option specifies the Ethernet interface to use.
  pppd 启动参数指定使用 eth0 （Ethernet card 以太网网卡名）；
• The role of pppd is managing PPP session establishment and session termination.

pppd & pppoe

ppp0 & eth0

• 通过 ppp0 获得外网IP；
• 通过 etho 获得 mac 地址；

Windows 拨号

宽带连接

接口适配器