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6.1 - System Management

1. 在 R1 Telnet R3 期間,R2 突然下線導致 R1 的 Management Session 掛掉沒有反應 (Management Session hung),如何防止此問題發生?(選 2 組)

ccie

  1. 使用 Control Plane Policing
  2. 使用 service tcp-keepalives-in 指令
  3. 使用 service tcp-keepalives-out 指令
  4. 使用 service tcp-small servers 指令
  5. 使用 vty line ACLs

B, C

當 R2 突然下線,R1 及 R3 沒法感知 Connection 已經斷掉,R1 會一直停留在 Management Session 不動,此狀態稱為 hung,必需要等待 TCP Timeout (沒有特定時間) 後才能操作。使用 tcp-keepalives-in 和 tcp-keepalives-out 設定如下:

R1(config)#service tcp-keepalives-out
R3(config)#service tcp-keepalives-in

這樣做,R1 和 R3 每分鐘會發 TCP Keepalives Message 給對方,當對方連續 4 次不回應,則 TCP Connection 被強制中斷。

*Oct  6 00:41:54.259: TCB65B25FB8 connected to 192.168.23.3.23
*Oct 6 00:41:57.355: TCP0: keepalive timeout (0/4) *Oct 6 00:42:57.355: TCP0: keepalive timeout (0/4) *Oct 6 00:43:57.355: TCP0: keepalive timeout (1/4) *Oct 6 00:44:57.355: TCP0: keepalive timeout (2/4) *Oct 6 00:45:57.355: TCP0: keepalive timeout (3/4) *Oct 6 00:46:57.355: TCP0: keepalive timeout (4/4) *Oct 6 00:46:57.355: TCP0: state was ESTAB -> CLOSED [63097 -> 192.168.23.3(23)] *Oct 6 00:46:57.359: TPA: Released port 63097 in Transport Port Agent for TCP IP type 1 delay 240000 *Oct 6 00:46:57.363: TCB 0x65B25FB8 destroyed