现场组网中S5560X作为汇聚设备,下联多台20+台IE4320呈链状连接,stp的规模超过了20台。
以下“设备”均为IE4320
S5560X(根桥)—设备2---设备3---设备4---……--设备20—设备21---……
(1)首先通过在21台设备上debug和抓包,发现故障时该设备能够收到来自于根桥的bpdu,但是并未继续处理,上行口1/0/9作为指定端口却处于discarding状态,还会往外发送bpdu:
===============display stp brief===============
MST ID Port Role STP State Protection
0 GigabitEthernet1/0/1 DESI FORWARDING NONE
0 GigabitEthernet1/0/9 DESI DISCARDING NONE
0 GigabitEthernet1/0/10 ROOT FORWARDING NONE
看debug也收到了bpdu,指定端口收到bpdu导致的discarding:
Port9(GigabitEthernet1/0/9) received MSTP-dot1s Packet(Length: 102)
ProtocolVersionID: 03
BPDUType : 02
CIST Root ID : 0.f4e9-755e-ff20 //根桥
External RPC : 400
Reg Root ID : 32768.305f-7786-8eca
Internal RPC : 0
CIST Bridge ID : 32768.305f-7786-8eca
CIST Port ID : 128.9
(Instance)Flags : (00)Desi[ AFL ]
Port9(GigabitEthernet1/0/9) sent MSTP-dot1s Packet(Length: 102)
ProtocolVersionID: 03
BPDUType : 02
CIST Root ID : 32768.305f-7786-6ff2
External RPC : 20
Reg Root ID : 32768.305f-7786-d76a
Internal RPC : 0
CIST Bridge ID : 32768.305f-7786-d76a
CIST Port ID : 128.9
(Instance)Flags : (00)Desi[ A P ]
(2)查看第20台交换机上,stp状态正常,但是msgage已经到了19。经确认,当前stp的实现里,每经过一个桥转发bpdu,msgage也会+1,而根桥上默认的max-age为20s,所以当stp规模超过20之后,后续的设备收到对应bpdu将不会处理:
----[Port10(GigabitEthernet1/0/10)][FORWARDING]----
Port protocol : Enabled
Port role : Root Port (Boundary)
Port ID : 128.10
Port cost(Legacy) : COnfig=auto, Active=20
Desg.bridge/port : 32768.305f-7786-90fa, 128.10
Port edged : COnfig=disabled, Active=disabled
Point-to-Point : COnfig=auto, Active=true
Transmit limit : 10 packets/hello-time
TC-Restriction : Disabled
Role-Restriction : Disabled
Protection type : COnfig=none, Active=none
MST BPDU format : COnfig=auto, Active=802.1s
Port Config-
Digest-Snooping : Disabled
Rapid transition : True
Num of VLANs mapped : 3
Port times : Hello 2s MaxAge 20s FwdDelay 15s MsgAge 19s RemHops 20
BPDU sent : 246416
TCN: 0, Config: 0, RST: 0, MST: 246416
BPDU received : 839752
TCN: 0, Config: 0, RST: 0, MST: 839752
1、STP组网规模超过20时,除了需要修改max-hop外还需要同步修改stp timer max-age,每多一台需要加1跳、1秒。
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