Connectivity Guide

ethernet1/1/29
seq 10 deny ip any any fragment count (100 packets)
Clear access-list counters
Clear IPv4, IPv6, or MAC access-list counters for a specic access-list or all lists. The counter counts the number of packets that match
each permit or deny statement in an access-list. To get a more recent count of packets matching an access-list, clear the counters to start
at zero. If you do not congure an access-list name, all IP access-list counters clear.
To view access-list information, use the show access-lists command.
• Clear IPv4 access-list counters in EXEC mode.
clear ip access-list counters access-list-name
• Clear IPv6 access-list counters in EXEC mode.
clear ipv6 access-list counters access-list-name
• Clear MAC access-list counters in EXEC mode.
clear mac access-list counters access-list-name
IP prex-lists
IP prex-lists control the routing policy. An IP prex-list is a series of sequential lters that contain a matching criterion and an permit or
deny action to process routes. The lters process in sequence so that if a route prex does not match the criterion in the rst lter, the
second lter applies, and so on.
A route prex is an IP address pattern that matches on bits within the IP address. The format of a route prex is A.B.C.D/x, where
A.B.C.D is a dotted-decimal address and /x is the number of bits that match the dotted decimal address.
When the route prex matches a lter, the system drops or forwards the packet based on the lter’s designated action. If the route prex
does not match any of the lters in the prex-list, the route drops, an implicit deny.
For example, in 112.24.0.0/16, the rst 16 bits of the address 112.24.0.0 match all addresses between 112.24.0.0 to
112.24.255.255. Use permit or deny lters for specic routes with the le (less or equal) and ge (greater or equal) parameters, where
x.x.x.x/x represents a route prex:
• To deny only /8 prexes, 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 le 12
• 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 prex-lists:
• A prex-list without permit or deny lters allows all routes
• An implicit deny is assumed — the route drops for all route prexes that do not match a permit or deny lter
• After a route matches a lter, the lter’s action applies and no additional lters apply to the route
Use prex-lists in processing routes for routing protocols such as open shortest path rst (OSPF), route table manager (RTM), and border
gateway protocol (BGP).
To congure a prex-list, use commands in PREFIX-LIST and ROUTER-BGP modes. Create the prex-list in PREFIX-LIST mode and assign
that list to commands in ROUTER-BGP modes.
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Access Control Lists