alternate port 是根端口的替换端口；backup port 是指定端口的备份端口。看看思科的解释：(D：指定端口，R：根端口，A：替换端口，B：备份端口)An alternate port receives more useful BPDUs from another bridge and is a port blocked. A backup port receives more useful BPDUs from the same bridge it is on and is a...
