HP 6120XG HP ProCurve Series 6120 Blade Switches Advanced Traffic Management G - Page 178
Loop Protection, Examples of Loop Protection Enabled in Preference to STP
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Multiple Instance Spanning-Tree Operation Loop Protection Loop Protection In cases where spanning tree cannot be used to prevent loops at the edge of the network, loop protection may provide a suitable alternative. Unlike spanning tree, however, loop protection is not a comprehensive loop detection feature and should only be enabled on untagged edge ports, that is, ports that connect to unmanaged switches and/or clients at the edge of the network. The cases where loop protection might be chosen ahead of spanning tree to detect and prevent loops are as follows: ■ On ports with client authentication. When spanning tree is enabled on a switch that use 802.1X, Web authentication, and MAC authentication, loops may go undetected. For example, spanning tree packets that are looped back to an edge port will not be processed because they have a different broadcast/multicast MAC address from the client-authenticated MAC address. To ensure that client-authenticated edge ports get blocked when loops occur, you should enable loop protection on those ports. ■ On ports connected to unmanaged devices. Spanning tree cannot detect the formation of loops where there is an unmanaged device on the network that does not process spanning tree packets and simply drops them. Loop protection has no such limitation, and can be used to prevent loops on unmanaged switches. Figure 4-29 shows examples where loop protection can be used. STP Domain Spanning tree enabled ports Switch Loop protection enabled 'edge' ports that connect to unmanaged switches and/or authenticated clients Web authentication clients 802.1X authentication clients Unmanaged switch (does not support STP) Figure 4-29. Examples of Loop Protection Enabled in Preference to STP 4-70