STP (Spanning Tree Protocol)

 1. STP ( Spanning Tree Protocol )

       스위치의 MAC 주소 : show version
       우선 순위 값 : 32768 ( 기본 ) 

       우선 순위값.스위치의MAC주소 -> Bridge ID ( BID )

       BPDU ( Bridge Protocol Data Unit )
         -> Configuration BPDU ( 설정 BPDU ) 
             : 자신의 BID, Root Bridege의 BID, Cost, Port ID 등
              ------------
              Sender BID : 옛날 장비일수록 낮은 BID를 가짐

   Step 1. Root Bridge ( = Root Switch ) 선출  -> 1대

             조건 : 가장 낮은 BID를 가진 스위치

   Step 2. Non Root Bridge 들에서 하나의 Root Port를 선출
                                                ----
             Root Port : 해당 스위치에서 Root Bridge로 가는 길

           * Root Port 선출 조건 
              1) 가장 낮은 Cost 값

                 Cost 값은 인터페이스의 대역폭별로 사전에 정의 된 값
                    Fastethernet - 100Mpbs : 19
 

   * STP 상태 확인하는 명령어
      Switch# show spanning-tree



              2) 가장 낮은 Sender BID를 가진 프레임을 수신한 포트
                               ------------
                               현재 스위치와 연결된 스위치의 BID

              3) 가장 낮은 Sender Port ID를 가진 프레임을 수신한 포트


   Step 3. 각 세그먼트마다 하나의 Designated Port (지정 포트)를 선출
                 ----------
                스위치의 포트, 스위치간 링크


              0) 루트 브리치(스위치)의 모든 포트는 Designated Port이다.
              
              1) Cost

              2) Sender BID

              3) Port ID


  2. Spanning tree 상태 확인
       Switch# show spanning-tree
                >> BID ( 해당 스위치, Root Switch )
                     포트 이름 ( STP Role, STP Port Status )
                                          역할                 상태
                                     ---------                ------
                                    Root Port                Forwarding (전달)
                                    Designated Port       Forwarding (전달)
                                    Alternate Port          Blocking(BLK)


  3. STP 포트 상태 전이
       Blocking -> Listening -> Learning -> Forwarding
                   20초           15초           15초

       50초 : Blocking 상태에서 Forwarding 상태로 변경되기 까지의 시간

       Listening -> Learning -> Forwarding : 30초 ( PC와 연결된 포트 )

       30초 ~ 50초 : STP Convergence Time
                                --------------------
                                       수렴시간

  4. STP 디버그 명령어
      Switch# debug spanning-tree events ( 디버그 실행 )
      Switch#no debug spanning-tree events ( 해당 디버그 종료)


  5. 패스트 ( fast )
    1) 포트패스트 >> PC나 서버와 연결된 포트에 설정.
        Switch(config-if)# spanning-tree portfast
            >> 30초라는 수렴시간을 줄일 수 있음
        Switch(config-if)# switchport mode access
    2) 업링크 패스트
    3) 백본 패스트(Backbone)

  6. 게이트웨이 이중화
      기술 : HSRP, VRRP, GLBP

           시스코 전용 프로토콜 : HSRP, GLBP
           산업 표준 프로토콜 : VRRP

      -> 가상 라우터 ( Virtual Router ), 가상 IP, 가상 MAC 
      -> preempt 개념
          - 2대로 구성된 게이트웨이 이중화 환경에서 한 라우터가 고장나서 작동이
            안 될 때 나머지 한대가 게이트웨이 역할을 할 수 있게 해주는 기능