86 | Access Control Lists (ACLs)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m The following rules apply to prefix lists:• A prefix list without any permit or deny filters allows all routes.• An “implicit deny” is assumed (that is, the route is dropped) for all route prefixes that do not match apermit or deny filter in a configured prefix list.• After a route matches a filter, the filter’s action is applied. No additional filters are applied to the route.Implementation InformationIn FTOS, prefix lists are used in processing routes for routing protocols (for example, router informationprotocol [RIP], open shortest path first [OSPF], and border gateway protocol [BGP]).Configuration Task List for Prefix ListsTo configure a prefix list, you must use commands in PREFIX LIST, ROUTER RIP, ROUTER OSPF, andROUTER BGP modes. You create the prefix list in PREFIX LIST mode, and assign that list to commandsin ROUTER RIP, ROUTER OSPF, and ROUTER BGP modes.The following list includes the configuration tasks for prefix lists:• Configure a Prefix List• Use a Prefix List for Route RedistributionFor a complete listing of all commands related to prefix lists, refer to the FTOS Command Line InterfaceReference Guide.Configure a Prefix ListTo configure a prefix list, follow these steps, starting in CONFIGURATION mode:Note: The MXL Switch platform does not support all protocols. It is important to know which protocol youare supporting prior to implementing prefix lists.Step Command Syntax Command Mode Purpose1 ip prefix-list prefix-name CONFIGURATION Create a prefix list and assign it a uniquename.You are in PREFIX LIST mode.2 seq sequence-number {deny |permit} ip-prefix [gemin-prefix-length] [lemax-prefix-length]CONFIG-NPREFIXL Create a prefix list with a sequence numberand a deny or permit action. The optionalparameters are:• ge min-prefix-length: is the minimumprefix length to be matched (0 to 32).• le max-prefix-length: is the maximumprefix length to be matched (0 to 32).
