我应该自己解决这个问题，但实际上我似乎是个笨蛋。
我有两个 Cisco 3750X 堆栈，每个堆栈中有两个交换机。一个堆栈在建筑物 A 中，另一个堆栈在建筑物 B 中。每个堆栈充当建筑物的核心交换机和本地流量的路由器。此外，两个堆栈之间共享一些 VLAN，但没有路由。
堆栈通过暗光纤和 1Gbps 单模 SFP 连接。这就像一个魅力。
现在，我们要在两个堆栈之间安装第二个上行链路以进行备份。不幸的是，我们只能在建筑物之间租用 100 Mbit (STM-100) 以太网线路，因此无法使用端口通道/以太网通道。
然后我想：只需将第二个端口配置为与第一个上行链路端口相同的设置（中继）并插入线路。由于成本较高，生成树将禁用它，并在主上行链路（Gbit 光纤）发生故障时启用它。还有一个问题：
生成树 (RSTP) 已禁用“新”端口，但将其检测为“备份”并使其丢弃所有数据包，并且在主上行链路出现故障时不启用它。
问题是：如果主线路发生故障，我如何让堆栈启用备用线路，或者如果这不可能，那么实现相同目标的更好方法是什么。
这是一个简单的绘图来可视化问题：
运行配置的相关部分：
堆叠在A楼：
interface GigabitEthernet1/0/28
description downlink trunk BldB
switchport access vlan 666
switchport trunk encapsulation dot1q
switchport trunk native vlan 666
switchport trunk allowed vlan 2-99,101-199,201-4094
switchport mode trunk
switchport nonegotiate
speed nonegotiate
end
interface GigabitEthernet2/0/28
description "downlink trunk BldgB 100M-Backup"
switchport access vlan 666
switchport trunk encapsulation dot1q
switchport trunk native vlan 666
switchport trunk allowed vlan 2-99,101-109,111-4094
switchport mode trunk
switchport nonegotiate
shutdown
speed 100
duplex full
spanning-tree vlan 99 port-priority 128
spanning-tree vlan 99 cost 50
end
B楼的堆栈：
interface GigabitEthernet1/0/1
description downlink trunk BldgA
switchport access vlan 666
switchport trunk encapsulation dot1q
switchport trunk native vlan 666
switchport trunk allowed vlan 2-99,101-199,201-4094
switchport mode trunk
switchport nonegotiate
speed nonegotiate
duplex full
end
interface GigabitEthernet2/0/1
description "downlink trunk BldgA 100Mbit-Backup"
switchport access vlan 666
switchport trunk encapsulation dot1q
switchport trunk native vlan 666
switchport trunk allowed vlan 2-99,101-109,111-4094
switchport mode trunk
switchport nonegotiate
speed 100
duplex full
end
编辑：添加生成树信息：
bldga-core# show spanning-tree summary
Switch is in rapid-pvst mode
Root bridge for: VLAN0099, VLAN0101-VLAN0117, VLAN0200
Extended system ID is enabled
Portfast Default is disabled
PortFast BPDU Guard Default is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default is disabled
EtherChannel misconfig guard is enabled
UplinkFast is disabled
Stack port is StackPort1
BackboneFast is disabled
Configured Pathcost method used is short
bldgb-core# show spanning-tree summary
Switch is in rapid-pvst mode
Root bridge for: VLAN0100, VLAN0110, VLAN0118, VLAN0200
EtherChannel misconfig guard is enabled
Extended system ID is enabled
Portfast Default is disabled
PortFast BPDU Guard Default is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default is disabled
UplinkFast is disabled
Stack port is StackPort1
BackboneFast is disabled
Configured Pathcost method used is short
bldga-core# show spanning-tree vlan 99
VLAN0099
Spanning tree enabled protocol rstp
Root ID Priority 99
Address 081f.f31e.9c80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 99 (priority 0 sys-id-ext 99)
Address 081f.f31e.9c80
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Po14 Desg FWD 3 128.592 P2p
Po15 Desg FWD 3 128.600 P2p
Po17 Desg FWD 3 128.616 P2p
Po19 Desg FWD 3 128.632 P2p
Po22 Desg FWD 3 128.656 P2p
Po23 Desg FWD 3 128.664 P2p
Po24 Desg FWD 3 128.672 P2p
Po28 Desg FWD 4 128.704 P2p
bldgb-core#show spanning-tree vlan 99
VLAN0099
Spanning tree enabled protocol rstp
Root ID Priority 99
Address 081f.f31e.9c80
Cost 4
Port 616 (Port-channel14)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 4195 (priority 4096 sys-id-ext 99)
Address d072.dc9b.4980
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Po14 Root FWD 4 128.616 P2p
Po15 Desg FWD 4 128.624 P2p
Po16 Desg FWD 4 128.632 P2p
Po17 Desg FWD 4 128.640 P2p
Po18 Desg FWD 4 128.648 P2p
Po19 Desg FWD 4 128.656 P2p
Po20 Desg FWD 4 128.664 P2p
Po21 Desg FWD 4 128.672 P2p
Po22 Desg FWD 4 128.680 P2p
Po23 Desg FWD 4 128.688 P2p
Po25 Desg FWD 4 128.704 P2p
bldga-core#show interfaces gi2/0/28
GigabitEthernet2/0/28 is administratively down, line protocol is down (disabled)
Hardware is Gigabit Ethernet, address is 081f.f31e.c39c (bia 081f.f31e.c39c)
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 100Mb/s, link type is force-up, media type is 10/100/1000BaseTX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 20:35:08, output 20:34:56, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 6039
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
964013646 packets input, 740488440354 bytes, 0 no buffer
Received 3529649 broadcasts (2477004 multicasts)
0 runts, 0 giants, 0 throttles
12 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 2477004 multicast, 0 pause input
0 input packets with dribble condition detected
975352039 packets output, 923509356637 bytes, 0 underruns
0 output errors, 0 collisions, 9 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
0 output buffer failures, 0 output buffers swapped out
bldgb-core#show interfaces gigabitEthernet 2/0/1
GigabitEthernet2/0/1 is down, line protocol is down (notconnect)
Hardware is Gigabit Ethernet, address is 74a0.2f7e.3001 (bia 74a0.2f7e.3001)
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 100Mb/s, link type is auto, media type is 10/100/1000BaseTX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 20:25:27, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 346
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
160167 packets output, 19128660 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
bldga-core#show etherchannel summary
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 15
Number of aggregators: 15
Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SD) -
14 Po14(SU) - Gi1/0/14(P) Gi2/0/8(P)
15 Po15(SU) - Gi1/0/15(P) Gi2/0/9(P)
16 Po16(SD) - Gi2/0/16(D)
17 Po17(SU) - Gi1/0/17(P) Gi2/0/17(P)
18 Po18(SD) -
19 Po19(SU) - Gi1/0/22(P) Gi2/0/19(P)
20 Po20(SD) -
21 Po21(SD) -
22 Po22(SU) - Gi1/0/9(P) Gi2/0/10(P) Gi2/0/14(P)
Gi2/0/15(P)
23 Po23(SU) - Gi1/0/10(P) Gi1/0/18(P) Gi2/0/11(P)
Gi2/0/18(P)
24 Po24(SU) - Gi2/0/5(P) Gi2/0/6(P)
27 Po27(SD) - Gi2/0/23(D)
28 Po28(SU) - Gi1/0/28(P)
29 Po29(SD) -
谢谢你的帮助！