STP Loop 探讨

8月 27th, 2010,由 frank撰写

Topology：

7609（G5/2）-----------（G2/0/1）3750
                          G2/0/11  G2/0/12
                               |____|

环境：

76’s vlan 2: 73.1.1.7/24 37’s vlan 2: 73.1.1.3/24 生成树的根在7609上在3750上关闭vlan1的spanning tree，并把G0/11和G0/12环起来。

注：以下是MAC地址说明
00.1F.6D.5D.FC.80 ---> 3750 MAC, bridge MAC
00.1F.6D.5D.FC.81 ---> 3750 G2/0/1
01.80.C2.00.00.00 ---> STP, 802.1D BPDU
01.00.0C.CC.CC.CD ---> SSTP, PVST BPDU
00.1E.F7.41.3C.80 ---> 7609 MAC, root MAC
00.1E.BE.6E.79.DD ---> 7609 G5/2 MAC

目的：

通过这个实验，理解2层网络中环路的产生及环路的诊断。
由于无法模拟流量，所以最终无法模拟7609 CPU peak。

过程：

cisco7609#sh proc cpu sort
CPU utilization for five seconds: 0%/0%; one minute: 0%; five minutes: 1%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
   7      193872     16157      11999  0.95%  0.23%  0.23%   0 Check heaps
   1           0        10          0  0.00%  0.00%  0.00%   0 Chunk Manager 

cisco7609#
cisco7609#
cisco7609#remote login sw
Trying Switch ...
Entering CONSOLE for Switch
Type "^C^C^C" to end this session

cisco7609-sp#
cisco7609-sp#debug netdr capture rx
cisco7609-sp#
cisco7609-sp#no debug netdr capture rx
cisco7609-sp#
cisco7609-sp#sh netdr captured-packets
A total of 3910 packets have been captured
The capture buffer wrapped 0 times
Total capture capacity: 4096 packets

------- dump of incoming inband packet -------
interface NULL, routine mistral_process_rx_packet_inlin, timestamp 00:00:09
dbus info: src_vlan 0x1(1), src_indx 0x101(257), len 0x40(64)
  bpdu 1, index_dir 0, flood 0, dont_lrn 1, dest_indx 0x382(898)
  67000408 00010000 01010000 40020000 5E000000 00000000 00000000 03822000
mistral hdr: req_token 0x0(0), src_index 0x101(257), rx_offset 0x74(116)
  requeue 0, obl_pkt 0, vlan 0x1(1)
destmac 01.80.C2.00.00.00, srcmac 00.1F.6D.5D.FC.81, protocol 002E
protocol stp (linktype 19); values on paktype itself:
  vlan 1(0x1), srcidx 257(0x101), dstidx 898(0x382)
  addrstart 0x18000074, rxtype 64(0x40)

------- dump of incoming inband packet -------
interface NULL, routine mistral_process_rx_packet_inlin, timestamp 00:00:09
dbus info: src_vlan 0x1(1), src_indx 0x101(257), len 0x40(64)
  bpdu 1, index_dir 0, flood 0, dont_lrn 1, dest_indx 0x382(898)
  6F000408 00010000 01010000 40020000 5E000000 00000000 00000000 03822000
mistral hdr: req_token 0x0(0), src_index 0x101(257), rx_offset 0x74(116)
  requeue 0, obl_pkt 0, vlan 0x1(1)
destmac 01.80.C2.00.00.00, srcmac 00.1F.6D.5D.FC.81, protocol 002E
protocol stp (linktype 19); values on paktype itself:
  vlan 1(0x1), srcidx 257(0x101), dstidx 898(0x382)
  addrstart 0x18000074, rxtype 64(0x40)

------- dump of incoming inband packet -------
interface NULL, routine mistral_process_rx_packet_inlin, timestamp 00:00:13
dbus info: src_vlan 0x1(1), src_indx 0x101(257), len 0x40(64)
  bpdu 1, index_dir 0, flood 0, dont_lrn 1, dest_indx 0x382(898)
  77000408 00010000 01010000 40020000 5E000000 00000000 00000000 03822000
mistral hdr: req_token 0x0(0), src_index 0x101(257), rx_offset 0x74(116)
  requeue 0, obl_pkt 0, vlan 0x1(1)
destmac 01.80.C2.00.00.00, srcmac 00.1F.6D.5D.FC.81, protocol 002E
protocol stp (linktype 19); values on paktype itself:
  vlan 1(0x1), srcidx 257(0x101), dstidx 898(0x382)
  addrstart 0x18000074, rxtype 64(0x40)

!---从上面的抓包结果看，7609的SP收到了很多802.1D的BPDU，从3750的直连口G2/0/1发过来
!---3750已经关闭了vlan1的Spanning Tree，而且root在76上，所以初步判定这是环回来的BPDU
cisco7609-sp#exit

[Connection to Switch closed by foreign host]
cisco7609#
cisco7609#
cisco7609#sh span

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    4097
             Address     001e.f741.3c80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    4097   (priority 4096 sys-id-ext 1)
             Address     001e.f741.3c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi5/2               Desg BLK 4         128.1026 self-looped P2p

!---已经检测到VLAN1 自环并Block端口了，所以现在RP不受影响，但是SP仍然在收BPDU
VLAN0002
  Spanning tree enabled protocol ieee
  Root ID    Priority    32770
             Address     001e.f741.3c80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     001e.f741.3c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi5/2               Desg FWD 4         128.1026 P2p 

cisco7609#
cisco7609#sh span de

 VLAN0001 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 4096, sysid 1, address 001e.f741.3c80
  Configured hello time 2, max age 20, forward delay 15
  We are the root of the spanning tree
  Topology change flag not set, detected flag not set
  Number of topology changes 2 last change occurred 03:06:46 ago
          from GigabitEthernet5/2
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

 Port 1026 (GigabitEthernet5/2) of VLAN0001 is blocking, self-looped
   Port path cost 4, Port priority 128, Port Identifier 128.1026.
   Designated root has priority 4097, address 001e.f741.3c80
   Designated bridge has priority 4097, address 001e.f741.3c80
   Designated port id is 128.1026, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 33421, received 15639875
!---发现VLAN1 的 “Topology Change”没有变化，因为已经Block自环口，所以没有影响7609的STP
!---但是可以看到G5/2下收到了大量的BPDU，这样证明了前面的判定，这些都是环回来的BPDU
!---接下来确认SP CPU的利用率，发现STP受到一些影响，但并不严重

 VLAN0002 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, sysid 2, address 001e.f741.3c80
  Configured hello time 2, max age 20, forward delay 15
  We are the root of the spanning tree
  Topology change flag not set, detected flag not set
  Number of topology changes 1 last change occurred 12:55:54 ago
          from GigabitEthernet5/2
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 1, topology change 0, notification 0, aging 300

 Port 1026 (GigabitEthernet5/2) of VLAN0002 is forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.1026.
   Designated root has priority 32770, address 001e.f741.3c80
   Designated bridge has priority 32770, address 001e.f741.3c80
   Designated port id is 128.1026, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 23287, received 1

cisco7609#remote command switch show proc cpu sort

CPU utilization for five seconds: 12%/6%; one minute: 13%; five minutes: 11%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
 201      239876   6473036         37  2.31%  2.84%  2.19%   0 Spanning Tree
 162     1231696     29480      41780  1.75%  1.68%  1.68%   0 Vlan Statistics
 124      958568   8830988        108  1.19%  1.22%  1.20%   0 slcp process
   3        8680    245433         35  0.00%  0.00%  0.00%   0 DiagCard5/-1

cisco7609#

cisco3750#sh span

VLAN0002
  Spanning tree enabled protocol ieee
  Root ID    Priority    32770
             Address     001e.f741.3c80
             Cost        4
             Port        55 (GigabitEthernet2/0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     001f.6d5d.fc80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi2/0/1             Root FWD 4         128.55   P2p 

cisco3750#
cisco3750#
cisco3750#sh spanning-tree de

 VLAN0002 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, sysid 2, address 001f.6d5d.fc80
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 32770, address 001e.f741.3c80
  Root port is 55 (GigabitEthernet2/0/1), cost of root path is 4
  Topology change flag not set, detected flag not set
  Number of topology changes 0 last change occurred 13:04:29 ago
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

 Port 55 (GigabitEthernet2/0/1) of VLAN0002 is root forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.55.
   Designated root has priority 32770, address 001e.f741.3c80
   Designated bridge has priority 32770, address 001e.f741.3c80
   Designated port id is 128.1026, designated path cost 0
   Timers: message age 2, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 1, received 23523

cisco3750#
cisco3750#
cisco3750#sh proc cpu sort
CPU utilization for five seconds: 97%/5%; one minute: 83%; five minutes: 62%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
 182     3476359   3166488       1097 69.21% 62.95% 47.68%   0 Spanning Tree
 124       15798   1656780          9  9.56%  5.33%  1.61%   0 Hulc LED Process
  31        5815      6096        953  5.58%  3.22%  0.95%   0 Logger
  57        3735   3059720          1  1.43%  0.79%  0.25%   0 Fifo Error Detec
   4       52235      6108       8551  0.63%  0.11%  0.06%   0 Check heaps      

cisco3750#
cisco3750#debug spanning-tree bpdu receive
Spanning Tree BPDU Received debugging is on
cisco3750#
cisco3750#un all
All possible debugging has been turned off
cisco3750#
cisco3750#
cisco3750#sh log
Syslog logging: enabled (45509 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)
    Console logging: disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging: level debugging, 806764 messages logged, xml disabled,
                    filtering disabled
    Exception Logging: size (4096 bytes)
    Count and timestamp logging messages: disabled
    File logging: disabled
    Trap logging: level informational, 398 message lines logged

Log Buffer (4090000 bytes):

15:56:04: STP: VLAN0002 rx BPDU: config protocol = ieee, packet from GigabitEthernet2/0/1  , linktype SSTP , enctype 3, encsize 22
15:56:04: STP: enc 01 00 0C CC CC CD 00 1E BE 6E 79 DD 00 32 AA AA 03 00 00 0C 01 0B
15:56:04: STP: Data     00000000008002001EF7413C80000000008002001EF7413C8084020000140002000F00
15:56:04: STP: VLAN0002 Gi2/0/1:0000 00 00 00 8002001EF7413C80 00000000 8002001EF7413C80 8402 0000 1400 0200 0F00
15:56:04: STP(2) port Gi2/0/1 supersedes 0
15:56:06: STP: VLAN0002 rx BPDU: config protocol = ieee, packet from GigabitEthernet2/0/1  , linktype SSTP , enctype 3, encsize 22
15:56:06: STP: enc 01 00 0C CC CC CD 00 1E BE 6E 79 DD 00 32 AA AA 03 00 00 0C 01 0B
15:56:06: STP: Data     00000000008002001EF7413C80000000008002001EF7413C8084020000140002000F00
15:56:06: STP: VLAN0002 Gi2/0/1:0000 00 00 00 8002001EF7413C80 00000000 8002001EF7413C80 8402 0000 1400 0200 0F00
15:56:06: STP(2) port Gi2/0/1 supersedes 0
15:56:08: STP: VLAN0002 rx BPDU: config protocol = ieee, packet from GigabitEthernet2/0/1  , linktype SSTP , enctype 3, encsize 22
15:56:08: STP: enc 01 00 0C CC CC CD 00 1E BE 6E 79 DD 00 32 AA AA 03 00 00 0C 01 0B
15:56:08: STP: Data     00000000008002001EF7413C80000000008002001EF7413C8084020000140002000F00
15:56:08: STP: VLAN0002 Gi2/0/1:0000 00 00 00 8002001EF7413C80 00000000 8002001EF7413C80 8402 0000 1400 0200 0F00
15:56:08: STP(2) port Gi2/0/1 supersedes 0
!---3750正常接收到从root发来的vlan2的BPDU，2s一次。源是76的G5/2，目的是pvst的BPDU

cisco3750#clear logg
Clear logging buffer [confirm]
cisco3750#
cisco3750#debug spanning-tree switch rx process
Spanning Tree Switch Shim process receive bpdu debugging is on
cisco3750#sh log
Syslog logging: enabled (45509 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)
    Console logging: disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging: level debugging, 809222 messages logged, xml disabled,
                    filtering disabled
    Exception Logging: size (4096 bytes)
    Count and timestamp logging messages: disabled
    File logging: disabled
    Trap logging: level informational, 398 message lines logged

Log Buffer (4090000 bytes):

15:58:44: STP SW: PROC RX: Gi2/0/12 vlan 1 linktype ieee-st(19)
15:58:44: STP SW: SW FLOOD Gi2/0/12 1 linktype 19 (ieee-st) 0180.c200.0000
15:58:44: STP SW: PROC RX: Gi2/0/11 vlan 1 linktype ieee-st(19)
15:58:44: STP SW: SW FLOOD Gi2/0/11 1 linktype 19 (ieee-st) 0180.c200.0000
15:58:44: STP SW: PROC RX: Gi2/0/12 vlan 1 linktype ieee-st(19)
15:58:44: STP SW: SW FLOOD Gi2/0/12 1 linktype 19 (ieee-st) 0180.c200.0000
15:58:44: STP SW: PROC RX: Gi2/0/11 vlan 1 linktype ieee-st(19)
15:58:44: STP SW: SW FLOOD Gi2/0/11 1 linktype 19 (ieee-st) 0180.c200.0000
15:58:44: STP SW: PROC RX: Gi2/0/12 vlan 1 linktype ieee-st(19)
!---G2/0/11和G2/0/12反复接收到802.1D的BPDU，也就是vlan1的。

cisco3750#un all
All possible debugging has been turned off
cisco3750#
cisco3750#clear logg
Clear logging buffer [confirm]
cisco3750#
cisco3750#debug spanning-tree switch tx
Spanning Tree Switch Shim transmit bpdu debugging is on
cisco3750#
cisco3750#un all
All possible debugging has been turned off
cisco3750#
cisco3750#sh log
Syslog logging: enabled (45509 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)
    Console logging: disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging: level debugging, 834214 messages logged, xml disabled,
                    filtering disabled
    Exception Logging: size (4096 bytes)
    Count and timestamp logging messages: disabled
    File logging: disabled
    Trap logging: level informational, 398 message lines logged

Log Buffer (4090000 bytes):

16:01:41: STP SW: TX: bpdu of type ieee-st size 60 on GigabitEthernet2/0/1 1
16:01:41: STP SW: TX: bpdu of type ieee-st size 60 on GigabitEthernet2/0/12 1
16:01:41: STP SW: TX: bpdu of type ieee-st size 60 on GigabitEthernet2/0/1 1
16:01:41: STP SW: TX: bpdu of type ieee-st size 60 on GigabitEthernet2/0/11 1
16:01:41: STP SW: TX: bpdu of type ieee-st size 60 on GigabitEthernet2/0/1 1
16:01:41: STP SW: TX: bpdu of type ieee-st size 60 on GigabitEthernet2/0/12 1
!---从上面debug信息可以看出来，G2/0/11和G2/0/12一直在重复发送vlan1的BPDU

cisco3750#clear logg
Clear logging buffer [confirm]
cisco3750#
cisco3750#debug spanning-tree switch rx decode
Spanning Tree Switch Shim decode received packets debugging is on
cisco3750#
cisco3750#debug spanning-tree switch rx process
Spanning Tree Switch Shim process receive bpdu debugging is on
cisco3750#
cisco3750#un all
All possible debugging has been turned off
cisco3750#
cisco3750#
cisco3750#sh log
Syslog logging: enabled (45509 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)
    Console logging: disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging: level debugging, 880351 messages logged, xml disabled,
                    filtering disabled
    Exception Logging: size (4096 bytes)
    Count and timestamp logging messages: disabled
    File logging: disabled
    Trap logging: level informational, 398 message lines logged

Log Buffer (4090000 bytes):

16:04:42: STP SW: PROC RX: 0180.c200.0000<-001f.6d5d.fc8b type/len 002E
!---收到BPDU的源MAC地址，是从G2/0/12发来的
16:04:42:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/12
16:04:42:     42 42 03 SPAN
16:04:42:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
!---1001是16进制的，这是ROOT的BID
16:04:42:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00
!---这是发送BPDU桥的BID，这里正好都是ROOT
16:04:42: STP SW: SW FLOOD Gi2/0/12 1 linktype 19 (ieee-st) 0180.c200.0000
16:04:42: STP SW: PROC RX: 0180.c200.0000<-001f.6d5d.fc8c type/len 002E
16:04:42:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/11
16:04:42:     42 42 03 SPAN
16:04:42:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
16:04:42:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00
16:04:42: STP SW: SW FLOOD Gi2/0/11 1 linktype 19 (ieee-st) 0180.c200.0000
16:04:42: STP SW: PROC RX: 0180.c200.0000<-001f.6d5d.fc8b type/len 002E
16:04:42:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/12
16:04:42:     42 42 03 SPAN
16:04:42:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
16:04:42:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00

cisco3750#clear logg
Clear logging buffer [confirm]
cisco3750#
cisco3750#debug spanning-tree switch tx decode
Spanning Tree Switch Shim decode transmitted packets debugging is on
cisco3750#
cisco3750#debug spanning-tree switch tx
Spanning Tree Switch Shim transmit bpdu debugging is on
cisco3750#
cisco3750#un all
All possible debugging has been turned off
cisco3750#
cisco3750#
cisco3750#sh log
Syslog logging: enabled (46024 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)
    Console logging: disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging: level debugging, 890509 messages logged, xml disabled,
                    filtering disabled
    Exception Logging: size (4096 bytes)
    Count and timestamp logging messages: disabled
    File logging: disabled
    Trap logging: level informational, 404 message lines logged

Log Buffer (4090000 bytes):

16:07:01: STP SW: TX: 0180.c200.0000<-001f.6d5d.fc81 type/len 002E
16:07:01:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/1
16:07:01:     42 42 03 SPAN
16:07:01:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
16:07:01:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00
!---G2/0/1发出的BPDU，其实这个就是环回来的BPDU
16:07:01: STP SW: TX: 0180.c200.0000<-001f.6d5d.fc8b type/len 002E
16:07:01:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/11
16:07:01:     42 42 03 SPAN
16:07:01:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
16:07:01:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00
16:07:01: STP SW: TX: 0180.c200.0000<-001f.6d5d.fc81 type/len 002E
16:07:01:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/1
16:07:01:     42 42 03 SPAN
16:07:01:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
16:07:01:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00
16:07:01: STP SW: TX: 0180.c200.0000<-001f.6d5d.fc8c type/len 002E
16:07:01:     encap SAP linktype ieee-st vlan 1 len 60 on v1 Gi2/0/12
16:07:01:     42 42 03 SPAN
16:07:01:     CFG P:0000 V:00 T:00 F:00 R:1001 001e.f741.3c80 00000000
16:07:01:     B:1001 001e.f741.3c80 84.02 A:0000 M:1400 H:0200 F:0F00

!---发现“Topology Change”没有变化，因为已经Block自环口，所以没有影响7609的STP

2层网络中常见的组播地址

更详细的可以查看WIKI：Multicast address

Dst Address        Type Field  Usage
01-00-0C-CC-CC-CC  0x0802      CDP (Cisco Discovery Protocol), VTP (VLAN Trunking Protocol)
01-00-0C-CC-CC-CC  0x0104      Port Aggregation Protocol (PAgP)
01-00-0C-CC-CC-CC  0x0111      Unidirectional Link Detection (UDLD)
01-00-0C-CC-CC-CC  0x2004      Dynamic Trunking (DTP)
01-00-0C-CC-CC-CC  0x2000      Cisco Discovery Protocol
01-00-0C-CC-CC-CC  0x2003      VLAN Trunking (VTP)
01-00-0C-CC-CC-CD  0x0802      Cisco Shared Spanning Tree Protocol Address
01-00-0C-CC-CC-CD  0x200A      STP Uplink Fast
01-80-C2-00-00-00  0x0802      Spanning Tree Protocol (for bridges) IEEE 802.1D
01-80-C2-00-00-08  0x0802      Spanning Tree Protocol (for provider bridges) IEEE 802.1AD
01-80-C2-00-00-02  0x0809      Ethernet OAM Protocol IEEE 802.3ah
01-00-5E-xx-xx-xx  0x0800      IPv4 Multicast Address
33-33-00-00-00-00  0x86DD      IPv6 Neighbor Discovery
33-33-xx-xx-xx-xx  0x86DD      IPv6 Multicast Address (RFC 3307)

本文出自 Frank's Blog

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STP 角色选举的探讨«

»CCIE SP-OSPF 小结2-数据库

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august.seu说道：

8月 31, 2010 20:35

你好，
拜读您的文章，受益匪浅。
小弟是研究芯片的，最近在研读一款网卡芯片的Datasheet时，遇到了这样如下问题，需要兄台上层应用的一些指点
我知道将系统的MAC地址的1st octet的7th MSB设置为1是使得其进入unicast模式，但是有些这样的疑问，
1)将网卡设置为unicast模式时，接受网络包的状态是如何？
2)将网卡设置为unicast模式时，在上层有配置其只接受特定MAC网络包的控制接口吗？如有，这个控制接口的配置信息是什么？
烦请兄台指点，不胜感激
frank说道：

8月 31, 2010 21:08

你好august.seu,芯片级别的问题跟我们常见的网络知识还是有一定差别的。对于我们来说不是很care网卡的模式，而且我不太理解你所说的“unicast”模式，“promiscuous”模式到是我们常见的。如果可能，最好能翻译一下，或换种比较容易理解的说法。

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STP Loop 探讨

Topology：

环境：

目的：

过程：

2层网络中常见的组播地址

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