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Chapter 6

ECE495 Chapter Notes - Chapter 6: Private Network, Border Gateway Protocol, Logical Conjunction


Department
Electrical and Computer Engineering
Course Code
ECE495
Professor
mint
Chapter
6

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Route Filtering and Route-Maps v1.12 – Aaron Balchunas
* * *
All original material copyright © 2007 by
Aaron Balchunas (aaron@routeralley.com),
unless otherwise noted. All other material copyright © of their respective owners.
This material may be copied and used freely, but may not be altered or sold without the expressed written
consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
1
- Route Filtering and Route-Maps -
Prefix-Lists
Prefix-lists are used to match routes as opposed to traffic. Two things are
matched:
The prefix (the network itself)
The prefix-length (the length of the subnet mask)
Consider the following prefix-list:
Router(config)# ip prefix-list MYLIST 10.1.1.0/24
The above prefix-list matches the 10.1.1.0/24 network exactly. It will not
match 10.1.0.0/16, or 10.1.1.4/30.
A range of prefix-lengths can be specified:
Router(config)# ip prefix-list MYLIST 10.1.1.0/24 le 30
Router(config)# ip prefix-list MYLIST 10.1.1.0/24 ge 26 le 30
The first command dictates that the first 24 bits of the prefix must match
(meaning, the prefix must begin 10.1.1), and the subnet mask must be less
than or equal to 30 bits.
The second command dictates again that the first 24 bits of the prefix must
match, and the subnet mask must be between 26 to 30 bits (or equal to).
To match all prefixes:
Router(config)# ip prefix-list MYLIST 0.0.0.0/0 le 32
To view information about all prefix lists:
Router# show ip prefix-list detail

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

Route Filtering and Route-Maps v1.12 – Aaron Balchunas
* * *
All original material copyright © 2007 by
Aaron Balchunas (aaron@routeralley.com),
unless otherwise noted. All other material copyright © of their respective owners.
This material may be copied and used freely, but may not be altered or sold without the expressed written
consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
2
Distribute-Lists
Distribute-lists are used to filter routing updates, either inbound or
outbound. Routes must first be matched using an access-list or prefix-list,
and then applied using a distribute-list under the routing process:
To use an access-list to identify routes:
Router(config)# access-list 10 permit ip 172.16.0.0 0.0.255.255
Router(config)# router rip
Router(config-router)# distribute-list 10 in serial0/0
The above distribute-list will control routes sent inbound on serial0/0.
Specifically, the referenced access-list will only permit routes matching
172.16 in the first two octets.
To use a prefix-list to identify routes:
Router(config)# ip prefix-list MYLIST 10.1.0.0/16
Router(config)# router rip
Router(config-router)# distribute-list prefix MYLIST out fastethernet0/0
The above distribute-list will control routes sent outbound on
fastethernet0/0. Specifically, the referenced prefix-list will only match the
exact 10.1.0.0/16 route.
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