鏈路聚合的目的有以下兩點

提高 Bandwidth(頻寬)

假設把10組Cat 5e 的 port 結合起來就會變成 Cat 6 的網速，頻寬自然是提高了!但也是很有限的，你買10組Cat 5e 你幹嘛不買Cat 6就好了!!??

Redundancy(冗餘)

我們繼續上面的假設你有10組Cat 5e 的 port ，你如果9組 Cat 5e 因為些原因斷線，還有一條當作備援，雖然寬頻下降了，但你依然有網路服務。假設同一個時間10阻斷線，你就要檢討了。

V

• 手動配置模式(負載分擔模式、Static)

  手動配置模式->由於全部分擔及設置由手動輸入配置內容，所以稱手動配置模式

  負載分擔模式->由於被設置的全部網口都會參與分擔，所以稱負載分擔模式

  操作方法

  配置前狀態

  

  switch_1未配置前網口運作情況

  Switch_1#show spanning-tree 
  VLAN0001
    Spanning tree enabled protocol ieee
    Root ID    Priority    32769
               Address     0002.1662.159E
               Cost        19
               Port        1(FastEthernet0/1)
               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
  
    Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
               Address     00D0.BCBA.8E8C
               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
               Aging Time  20
  
  Interface        Role Sts Cost      Prio.Nbr Type
  ---------------- ---- --- --------- -------- --------------------------------
  Fa0/1            Root LRN 19        128.1    P2p //由這條得知Switch_1為RootSwitch(請參考補充1)
  Fa0/2            Altn BLK 19        128.2    P2p //由這條得知Switch_1 Fa0/2無法專發數據(請參考補充1)

  switch_2未配置前網口運作情況

  Switch_2#show spanning-tree 
  VLAN0001
    Spanning tree enabled protocol ieee
    Root ID    Priority    32769
               Address     0002.1662.159E
               This bridge is the root
               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
  
    Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
               Address     0002.1662.159E
               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
               Aging Time  20
  
  Interface        Role Sts Cost      Prio.Nbr Type
  ---------------- ---- --- --------- -------- --------------------------------
  Fa0/1            Desg FWD 19        128.1    P2p //正常運作中(請參考補充1)
  Fa0/2            Desg FWD 19        128.2    P2p //正常運作中(請參考補充1)

  補充1

  開始配置

  在設定PAgP時，應當先將網口關閉，以免造成網路風暴及設備損壞

  switch_1

  Switch_1(config)#interface range fastEthernet 0/1-2
  Switch_1(config-if-range)#shutdown 
  
  
  Switch_1(config-if-range)#
  %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to administratively down
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down
  
  %LINK-5-CHANGED: Interface FastEthernet0/2, changed state to administratively down
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to down
  
  Switch_1(config-if-range)#channel-group 1 mode on//將fastEthernet 0/1 fastEthernet 0/2放入Group1中
  Switch_1(config-if-range)#
  Creating a port-channel interface Port-channel 1

  switch_2

  Switch_2(config)#interface range fastEthernet 0/1-2
  Switch_2(config-if-range)#channel-group 1 mode on//將fastEthernet 0/1 fastEthernet 0/2放入Group1中並設為自動配置
  Switch_2(config-if-range)#
  Creating a port-channel interface Port-channel 1

  設定完畢後，即可開啟網口

  switch_1

  Switch_1(config-if-range)#no shutdown 
  
  
  Switch_1(config-if-range)#
  %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to up
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
  
  %LINK-5-CHANGED: Interface Port-channel1, changed state to up
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up
  
  %LINK-5-CHANGED: Interface FastEthernet0/2, changed state to up
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to up
  
  Switch_1(config-if-range)#

  switch_2

  Switch_2(config-if-range)#
  %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to up
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
  
  %LINK-5-CHANGED: Interface Port-channel1, changed state to up
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up
  
  %LINK-5-CHANGED: Interface FastEthernet0/2, changed state to up
  
  %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to up

  利用查看網口運作情況

  switch_1

  Switch_1#show etherchannel summary 
  Flags:  D - down        P - 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
          u - unsuitable for bundling
          w - waiting to be aggregated
          d - default port
  
  
  Number of channel-groups in use: 1
  Number of aggregators:           1
  
  Group  Port-channel  Protocol    Ports
  ------+-------------+-----------+----------------------------------------------
  
  1      Po1(SU)           -      Fa0/1(P) Fa0/2(P)

  switch_2

  Switch_2#show etherchannel summary 
  Flags:  D - down        P - 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
          u - unsuitable for bundling
          w - waiting to be aggregated
          d - default port
  
  
  Number of channel-groups in use: 1
  Number of aggregators:           1
  
  Group  Port-channel  Protocol    Ports
  ------+-------------+-----------+----------------------------------------------
  
  1      Po1(SU)           -      Fa0/1(P) Fa0/2(P)

• PAgP模式(Cisco獨有的技術)

  switch_1

  Switch_1(config)#interface range fastEthernet 0/1-2
  Switch_1(config-if-range)#channel-group 1 mode desirable//將fastEthernet 0/1 fastEthernet 0/2放入Group1中
  Switch_1(config-if-range)#
  Creating a port-channel interface Port-channel 1

  switch_2

  Switch_2(config)#interface range fastEthernet 0/1-2
  Switch_2(config-if-range)#channel-group 1 mode auto//將fastEthernet 0/1 fastEthernet 0/2放入Group1中
  Switch_2(config-if-range)#
  Creating a port-channel interface Port-channel 1

  

  • LACP模式

  switch_1

  Switch_1(config)#interface range fastEthernet 0/1-2
  Switch_1(config-if-range)#channel-group 1 mode Active//將fastEthernet 0/1 fastEthernet 0/2放入Group1中
  Switch_1(config-if-range)#
  Creating a port-channel interface Port-channel 1

  switch_2

  Switch_2(config)#interface range fastEthernet 0/1-2
  Switch_2(config-if-range)#channel-group 1 mode Passive//將fastEthernet 0/1 fastEthernet 0/2放入Group1中
  Switch_2(config-if-range)#
  Creating a port-channel interface Port-channel 1

  

• 負載平衡

  Switch(config)#port-channel load-balance ?
    dst-ip       Dst IP Addr
    dst-mac      Dst Mac Addr
    src-dst-ip   Src XOR Dst IP Addr
    src-dst-mac  Src XOR Dst Mac Addr
    src-ip       Src IP Addr
    src-mac      Src Mac Addr
  Switch(config)#port-channel load-balance

  • dst-ip
    目的地 ip

  • dst-mac
    目的地 mac

  • src-dst-ip
    請付費解鎖

  • src-dst-mac
    請付費解鎖

  • src-ip
    起點 ip

  • src-mac
    起點 mac

  通常題目會寫要使用哪一個，如果沒有特別說大部分都是dst-ip。

  • 接下來為廢話請酌量觀看

    在實務上沒有哪一個比較好，要看你用在哪裡?

    假設你是 web server(如下圖)， 你不可能用dst-ip或dst-mac那沒有任何的意義。

    

    則會使用 src-mac 因為 NAT 為了安全並不會讓外部帶著原ip(1.1.1.1)進入，而是使用Router(192.168.1.254)的LAN ip 則 src- ip 就會落得與 dst-ip 及 dst-mac 相同的處境。