昨天，当我们的 BGP 路由之一出现短时间故障时，我们的网络出现了短暂中断。幸运的是，我们的连接在几分钟后故障转移到了我们的辅助 BGP 路由，并且主路由在 ISP 端关闭/不关闭后开始运行。
我们正在运行 2 个运行 iOS 12.2 58 的堆叠（背板）Cisco 3750e 交换机。
在我与我们的 ISP 的对话中，他们无法对原因给出任何明确的答案。我们可以做些什么来查明我们最终的原因以避免将来出现此问题？
出错时的日志
172258: May 6 14:43:06: %BGP-5-ADJCHANGE: neighbor xxx.xxx.12.34 Down BGP Notification sent
172259: May 6 14:43:06: %BGP-3-NOTIFICATION: sent to neighbor xxx.xxx.12.34 4/0 (hold time expired) 0 bytes
172260: May 6 14:43:06: %BGP_SESSION-5-ADJCHANGE: neighbor xxx.xxx.12.34 IPv4 Multicast topology base removed from session BGP Notification sent
172261: May 6 14:43:06: %BGP_SESSION-5-ADJCHANGE: neighbor xxx.xxx.12.34 IPv4 Unicast topology base removed from session BGP Notification sent
记录 ISP 何时关闭/不关闭以在他们这边重置 BGP
172542: May 6 15:04:15: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/49, changed state to down
172543: May 6 15:04:16: %LINK-3-UPDOWN: Interface GigabitEthernet2/0/49, changed state to down
172544: May 6 15:04:16: %PIM-5-NBRCHG: neighbor xxx.xxx.12.34 DOWN on interface GigabitEthernet2/0/49 non DR
172545: May 6 15:04:16: %PIM-5-NBRCHG: neighbor xxx.xxx.12.34 UP on interface GigabitEthernet2/0/49
172546: May 6 15:04:16: %PIM-5-DRCHG: DR change from neighbor 0.0.0.0 to xxx.xxx.12.35 on interface GigabitEthernet2/0/49
172547: May 6 15:04:18: %LINK-3-UPDOWN: Interface GigabitEthernet2/0/49, changed state to up
172548: May 6 15:04:19: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/49, changed state to up
BGP 连接最终从空闲状态变为 Up 时的日志
172828: May 6 15:27:33: %BGP-5-ADJCHANGE: neighbor xxx.xxx.12.34 Up
我们这边的 BGP 接口（注意：没有 CRC、丢包、冲突报告……）
GigabitEthernet2/0/49 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is xxxx.xxxx
Internet address is xxx.xxx.12.35/31
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 3/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX SFP
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:09, output 00:00:12, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/52/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 14536000 bits/sec, 1655 packets/sec
5 minute output rate 1010000 bits/sec, 640 packets/sec
413176726 packets input, 428902543141 bytes, 0 no buffer
Received 143495 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 139275 multicast, 0 pause input
0 input packets with dribble condition detected
125748632 packets output, 42915625632 bytes, 0 underruns
0 output errors, 0 collisions, 0 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