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Using Multiple Route Filters
In the “from and to” section earlier in this chapter, we saw that the application of multiple
match conditions in a term results in a logical AND operation. When multiple route filters are
used in a single term, this process is changed somewhat. In this situation, the multiple route
filters are evaluated much like a logical OR in that only one of the route filters will actually be
the match criteria used. This one route filter is found by performing a longest-match lookup
on the configured prefix/prefix-length within each route filter. Only after this longest-
match lookup is completed will the match type be considered to see if a candidate route actu-
ally matches the policy term.
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解释如下：
在一般情况下，同一term中的多个匹配条件（match conditions ）之间是
逻辑与关系，但在同一term中使用多个路由过滤器（ route filters）作为匹配条件的时候，情况有所改变，更像是一种逻辑或关系，但不完全是逻辑或。在这种情况下，多个路由过滤器都会被检查但只有一个会被当作匹配标准使用。
哪一个路由过滤器会被当作匹配标准呢？This one route filter is found by performing a longest-match lookup
on the configured prefix/prefix-length within each route filter，说得很清楚，对term里所列出的所有路由过滤器进行longest-match lookup最长匹配查找，最长匹配的那一条就是用于进行匹配与否判断的，只有最长匹配结束，选择出了最长匹配的过滤器，才通过该过滤器的匹配类型match-type来判断候选路由是否匹配，如果匹配则执行本term的action，如果不符合，则直接进入下一term（如果有）或者下一policy，而不是逐步缩短掩码检查本term的其他过滤器。
