Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring Routing Information (Rev. 03)
Controlling and Modifying Routing Information
© 2008 Foundry Networks, Inc.
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Access list statements are entered one per line, and the list is scanned for a match in the order at
which the statements were entered. Once the first match is found the rest of the access list is
ignored. Therefore, the most specific matches should appear early in the list.
NOTE
To create a routing access list the user should specify the protocol to filter, assign a
name to the access list, and define filtering criteria.
To create an IP access list the user should specify the protocol to filter, assign a
unique number
to the access list and define filtering criteria.
Understanding IP Prefix
A prefix list provides a powerful prefix-based filtering mechanism. The user can use prefix lists as
an alternative to access lists in many route-filtering commands.
The
ip prefix-list
command allows the following options:
•
The user can specify a lower and/or an upper range-limit to the prefix mask, using integer
values between 0 and 32.
•
The user can place the configured prefix-list entry in a specified position in the prefix-list, by
using sequential numbering in the range <1-4294967295>. To use this option, the user must
first enable sequence numbering.
By default, sequence numbers are generated automatically (unless the user enables sequence
numbering). If the user enables sequence numbering, the user must specify the sequence number
(in the range <1-4294967295>) for each entry of the IP prefix-list command.
Whether sequence numbers are generated automatically or entered manually, they determine the
order in which all prefix-list entries are scanned (proceeding in natural order from the lowest
sequence number to the highest).
Automatically generated sequence numbering is done according to the following rules:
•
The increment between two consecutive numbers that are automatically sequenced is 5.
•
If the user creates an automatically sequenced prefix-list entry following a manually sequenced
one, the new sequence number is the next available multiple of 5 that follows the highest
existing sequence number. For example, if a prefix-list entry with number 2 already exists and
the user creates a new entry without specifying a sequence number, the next entry will be
numbered 5. If lists 2 and 7 already exist and a new list is created without specifying a
sequence number, the new list will be numbered 10.
Route Maps Overview
Route maps provide an advanced filtering mechanism used both to control and modify routing
information and to specify the criteria for permitting or denying redistribution of routes between
routing devices. Route maps consist of a list of match and set clauses that specify the required
criteria and the actions to perform if these criteria are met.
In addition to the access lists and prefix lists functions, the user can use route maps to set up rules
for changing the routing information.
Configuring Routing Filters
Filtering Commands
Table 11
lists the commands that are used for filtering routing information.