Service Manual

• 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 prex lists:
• A prex list without any permit or deny lters allows all routes.
• An “implicit deny” is assumed (that is, the route is dropped) for all route prexes that do not match a permit or deny lter in a
congured prex list.
• After a route matches a lter, the lter’s action is applied. No additional lters are applied to the route.
Implementation Information
In Dell Networking OS, prex lists are used in processing routes for routing protocols (for example, router information protocol [RIP],
open shortest path rst [OSPF], and border gateway protocol [BGP]).
NOTE: It is important to know which protocol your system supports prior to implementing prex-lists.
Conguration Task List for Prex Lists
To congure a prex list, use commands in PREFIX LIST, ROUTER RIP, ROUTER OSPF, and ROUTER BGP modes.
Create the prex list in PREFIX LIST mode and assign that list to commands in ROUTER RIP, ROUTER OSPF and ROUTER BGP
modes.
The following list includes the conguration tasks for prex lists, as described in the following sections.
• Conguring a prex list
• Use a prex list for route redistribution
For a complete listing of all commands related to prex lists, refer to the Dell Networking OS Command Line Interface Reference
Guide.
Creating a Prex List
To create a prex list, use the following commands.
1. Create a prex list and assign it a unique name.
You are in PREFIX LIST mode.
CONFIGURATION mode
ip prefix-list prefix-name
2. Create a prex list with a sequence number and a deny or permit action.
CONFIG-NPREFIXL mode
seq sequence-number {deny | permit} ip-prefix [ge min-prefix-length] [le max-prefix-
length]
The optional parameters are:
• ge min-prefix-length: the minimum prex length to match (from 0 to 32).
• le max-prefix-length: the maximum prex length to match (from 0 to 32).
Example of Assigning Sequence Numbers to Filters
If you want to forward all routes that do not match the prex list criteria, congure a prex list lter to permit all routes (permit
0.0.0.0/0 le 32). The “permit all” lter must be the last lter in your prex list. To permit the default route only, enter permit
0.0.0.0/0.
Access Control Lists (ACLs)
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