Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 124

Counting ACL Hits You can view the number of packets matching the ACL by using the count option when creating ACL entries. 1 Create an ACL that uses rules with the count option. Refer to Configure a Standard IP ACL Filter. 2 Apply the ACL as an inbound or outbound ACL on an interface. Refer to Applying an IP ACL. 3 show ip accounting access-list EXEC Privilege mode View the number of packets matching the ACL. IP Prefix Lists IP prefix lists are supported to control routing policy. An IP prefix list is a series of sequential filters that contain a matching criterion (examine IP route prefix) and an action (permit or deny) to process routes. The filters are processed in sequence so that if a route prefix does not match the criterion in the first filter, the second filter (if configured) is applied. When the route prefix matches a filter, the system drops or forwards the packet based on the filter's designated action. If the route prefix does not match any of the filters in the prefix list, the route is dropped (that is, implicit deny). A route prefix is an IP address pattern that matches on bits within the IP address. The format of a route prefix is A.B.C.D/X where A.B.C.D is a dotted-decimal address and /X is the number of bits that should be matched of the dotted decimal address. For example, in 112.24.0.0/16, the first 16 bits of the address 112.24.0.0 match all addresses between 112.24.0.0 to 112.24.255.255. The following examples show permit or deny filters for specific routes using the le and ge parameters, where x.x.x.x/x represents a route prefix: • To deny only /8 prefixes, enter deny x.x.x.x/x ge 8 le 8. • To permit routes with the mask greater than /8 but less than /12, enter permit x.x.x.x/x ge 8. • To deny routes with a mask less than /24, enter deny x.x.x.x/x le 24. • To permit routes with a mask greater than /20, enter permit x.x.x.x/x ge 20. 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 a permit 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 Information Prefix lists are used in processing routes for routing protocols (for example, router information protocol [RIP], open shortest path first [OSPF], and border gateway protocol [BGP]). NOTE: It is important to know which protocol your system supports prior to implementing prefix-lists. Configuration Task List for Prefix Lists To configure a prefix list, use commands in PREFIX LIST, ROUTER RIP, ROUTER OSPF, and ROUTER BGP modes. Create the prefix list in PREFIX LIST mode and assign that list to commands in ROUTER RIP, ROUTER OSPF and ROUTER BGP modes. Access Control Lists (ACLs) 124