可以使用 PPP 和标准的 UNIX 实用程序来确定 PPPoE 问题。如果怀疑链路问题是由 PPPoE 所致，可使用以下诊断工具获取故障排除信息。
以下示例显示了为具有 PPPoE 隧道的链路生成的日志文件的一部分。
Sep 6 16:28:45 enyo pppd[100563]: [ID 702911 daemon.info] Plugin pppoe.so loaded. Sep 6 16:28:45 enyo pppd[100563]: [ID 860527 daemon.notice] pppd 2.4.0b1 (Sun Microsystems, Inc., Sep 5 2001 10:42:05) started by troot, uid 0 Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.debug] connect option: '/usr/lib/inet/pppoec -v hme0' started (pid 100564) Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.info] Serial connection established. Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.info] Using interface sppp0 Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.notice] Connect: sppp0 <--> /dev/sppptun Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.debug] /etc/ppp/pap-secrets is apparently empty Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.debug] /etc/ppp/chap-secrets is apparently empty Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.debug] sent [LCP ConfReq id=0xef <mru 1492> asyncmap 0x0 <magic 0x77d3e953><pcomp><acomp> Sep 6 16:28:46 enyo pppd[100563]: [ID 702911 daemon.debug] rcvd [LCP ConfReq id=0x2a <mru 1402> asyncmap 0x0 <magic 0x9985f048><pcomp><acomp
# pppd connect "/usr/lib/inet/pppoec -v interface-name"
pppoec 将诊断信息发送到 stderr。如果在前台运行 pppd，输出将显示在屏幕上。如果在后台运行 pppd，输出将发送到 /etc/ppp/connect-errors。
以下示例展示了协商 PPPoE 隧道时生成的消息。
Connect option: '/usr/lib/inet/pppoec -v hme0' started (pid 100564) /usr/lib/inet/pppoec: PPPoE Event Open (1) in state Dead (0): action SendPADI (2) /usr/lib/inet/pppoec: Sending PADI to ff:ff:ff:ff:ff:ff: 18 bytes /usr/lib/inet/pppoec: PPPoE State change Dead (0) -> InitSent (1) /usr/lib/inet/pppoec: Received Active Discovery Offer from 8:0:20:cd:c1:2/hme0:pppoed /usr/lib/inet/pppoec: PPPoE Event rPADO+ (5) in state InitSent (1): action SendPADR+ (5) /usr/lib/inet/pppoec: Sending PADR to 8:0:20:cd:c1:2: 22 bytes /usr/lib/inet/pppoec: PPPoE State change InitSent (1) -> ReqSent (3) /usr/lib/inet/pppoec: Received Active Discovery Session-confirmation from 8:0:20:cd:c1:2/hme0:pppoed /usr/lib/inet/pppoec: PPPoE Event rPADS (7) in state ReqSent (3): action Open (7) /usr/lib/inet/pppoec: Connection open; session 0002 on hme0:pppoe /usr/lib/inet/pppoec: PPPoE State change ReqSent (3) -> Convers (4) /usr/lib/inet/pppoec: connected
如果通过该诊断消息无法确定问题，请继续执行此过程。
有关 snoop 的信息，请参阅 snoop(1M) 手册页。
# snoop -o pppoe-trace-file
# snoop -i pppoe-trace-file -v pppoe
ETHER: ----- Ether Header ----- ETHER: ETHER: Packet 1 arrived at 6:35:2.77 ETHER: Packet size = 32 bytes ETHER: Destination = ff:ff:ff:ff:ff:ff, (broadcast) ETHER: Source = 8:0:20:78:f3:7c, Sun ETHER: Ethertype = 8863 (PPPoE Discovery) ETHER: PPPoE: ----- PPP Over Ethernet ----- PPPoE: PPPoE: Version = 1 PPPoE: Type = 1 PPPoE: Code = 9 (Active Discovery Initiation) PPPoE: Session Id = 0 PPPoE: Length = 12 bytes PPPoE: PPPoE: ----- Service-Name ----- PPPoE: Tag Type = 257 PPPoE: Tag Length = 0 bytes PPPoE: PPPoE: ----- Host-Uniq ----- PPPoE: Tag Type = 259 PPPoE: Tag Length = 4 bytes PPPoE: Data = Ox00000002 PPPoE: . . . ETHER: ----- Ether Header ----- ETHER: ETHER: Packet 5 arrived at 6:35:2.87 ETHER: Packet size = 60 bytes ETHER: Destination = 8:0:20:78:f3:7c, Sun) ETHER: Source = 0:2:fd:39:7f:7, ETHER: Ethertype = 8864 (PPPoE Session) ETHER: PPPoE: ----- PPP Over Ethernet ----- PPPoE: PPPoE: Version = 1 PPPoE: Type = 1 PPPoE: Code = 0 (PPPoE Session) PPPoE: Session Id = 24383 PPPoE: Length = 20 bytes PPPoE: PPP: ----- Point-to-Point Protocol ----- PPP: PPP-LCP: ----- Link Control Protocol ----- PPP-LCP: PPP-LCP: Code = 1 (Configure Request) PPP-LCP: Identifier = 80 PPP-LCP: Length = 18