Reference Guide

seq 10 deny icmp any any
seq 10 deny icmp any any
For more information, refer to the VTY Line Local Authentication and Authorization section in the
Securitychapter.
IP Prefix Lists
IP prefix lists 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, Dell Networking OS 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
In Dell Networking OS, 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]).
It is important to know which protocol your system supports prior to implementing prefix-lists.
NOTE: The S5000 platform does not support all protocols. It is important to know which protocol
you are supporting 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)
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