Downloads |
Table Of Contents
EIGRP Support for Leaking Routes
Prerequisites for EIGRP Route Leaking
Information About EIGRP Route Leaking
EIGRP Automatic Summarization to the Network Level
Benefit of EIGRP Route Leaking
Behavior if EIGRP Route Leaking Is Configured Incompletely
How to Configure EIGRP Route Leaking
Configuring an EIGRP Summary Address to Leak a Component Route
Configuration Examples for EIGRP Route Leaking
Feature Information for EIGRP Route Leaking
EIGRP Support for Leaking Routes
First Published: November 16, 2006Last Updated: October 26, 2007The EIGRP Support for Leaking Routes feature introduces the capability to advertise a component route of a manual summary address that would otherwise be suppressed. Any component subset of the summary address can be leaked. The benefit of route leaking is that the leaked route is more specific than a summarized route and is therefore preferred.
Finding Feature Information in This Module
Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for EIGRP Route Leaking" section.
Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•
Prerequisites for EIGRP Route Leaking
•
•
•
•
Prerequisites for EIGRP Route Leaking
•
•
http://www.ciscopress.com/articles/article.asp?p=174107&seqNum=38rl=1&rl=1Information About EIGRP Route Leaking
You should understand the following concepts before configuring EIGRP route leaking:
•
•
•
EIGRP Automatic Summarization to the Network Level
EIGRP summarizes routes to the network level by default. Summarization is controlled by the auto-summary command; use the no form of this command to enable subnet-level route summarization.
Benefit of EIGRP Route Leaking
The benefit of route leaking (advertising a route) is that the leaked route is more specific than a summarized route and is therefore the preferred route. By using route leaking, you can prefer one path over another. Suppose you have a network with Routers A, B, and C, as shown in Figure 1.
Figure 1 EIGRP Route Leaking
You want to summarize routes to Router A for destinations within the summary, but you want to prefer the path through Router B for one subnet contained within the summary. Configure Router C to send only the summary 10.1.2.0/23. The longer match of 10.1.3.0/24 that is leaked through Router B is preferred and the 10.1.2.0/23 is available as a backup through Router C.
If we look at Router B, Router B would advertise a summary address of 10.1.2.0/23, as well as the more specific 10.1.3.0/24 permitted in the leak list specified in the ip summary-address eigrp command as 10.1.2.0 with a mask of 255.255.254.0 in the following configuration file:
Router B
interface serial 1ip address 10.1.3.4 255.0.0.0ip summary-address eigrp 3 10.1.2.0 255.255.254.0 leak-map LEAK-10-1-0!router eigrp 3network 10.1.0.0 0.0.255.255no auto-summary!access-list 2 permit 10.1.3.0 255.255.255.0route-map LEAK-10-1-0 permitmatch ip address 2Router C
interface serial 1ip address 10.1.3.5 255.0.0.0ip summary-address eigrp 3 10.1.2.0 255.255.254.0!router eigrp 3network 10.1.0.0 0.0.255.255no auto-summaryBehavior if EIGRP Route Leaking Is Configured Incompletely
The following default behavior occurs if the ip summary-address eigrp command is configured using the leak-map keyword and either the route map or access list is not configured:
•
•
How to Configure EIGRP Route Leaking
This section contains the following task:
•
Configuring an EIGRP Summary Address to Leak a Component Route
There might be times when you have summarized routes, but you want a particular route to be advertised. The benefit of route leaking (advertising a route) is that the leaked route is more specific than a summarized route and is therefore the preferred route. Perform this task to leak an EIGRP route that would otherwise be suppressed by a summary route.
In general, leaking an EIGRP route is achieved by defining a standard IP access list (or IP prefix list) to identify the component route as a source address. Then the access list is referenced in a route map (in a match ip address command), and the route map is referenced by the leak-map keyword in the ip summary-address eigrp command.
You can use a single access list to permit all the routes that you want to leak through a single summary.
SUMMARY STEPS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
DETAILED STEPS
Configuration Examples for EIGRP Route Leaking
This section contains the following example:
EIGRP Route Leaking: Example
The following example configures the 10.1.1.0/24 subnet to be leaked through the 10.0.0.0 summary address:
Router(config)# router eigrp 1Router(config-router)# exitRouter(config)# access-list 3 permit 10.1.1.0 0.0.0.255Router(config)# !Router(config)# route-map LEAK-10-1-1 permit 10Router(config-route-map)# match ip address 3Router(config-route-map)# exitRouter(config)# interface Serial 0/0Router(config-if)# ip summary-address eigrp 1 10.0.0.0 255.0.0.0 leak-map LEAK-10-1-1Router(config-if)# endAdditional References
The following sections provide references related to the EIGRP Support for Leaking Routes feature.
Related Documents
EIGRP commands
•
EIGRP configuration tasks
•
Route summarization
•
•
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
—
Technical Assistance
Command Reference
This section documents the following modified command only:
•
ip summary-address eigrp
To configure a summary aggregate address for a specified interface, use the ip summary-address eigrp command in interface configuration mode. To disable the summarization, use the no form of this command.
ip summary-address eigrp as-number ip-address mask [admin-distance] [leak-map name]
no ip summary-address eigrp as-number ip-address mask
Syntax Description
Defaults
No summary addresses are predefined.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
12.0(7)T
The admin-distance argument was added.
12.3(14)T
The leak-map keyword and name argument were added.
Usage Guidelines
The ip summary-address eigrp command is used to configure interface-level address summarization. EIGRP summary routes are given an administrative distance value of 5. The administrative distance metric is used to advertise a summary without installing it in the routing table.
By default, EIGRP summarizes subnet routes to the network level, even for a single host route. The no auto-summary command can be entered to configure subnet level summarization.
EIGRP Support for Leaking Routes
Configuring the leak-map keyword allows the router to advertise a component route that would otherwise be suppressed by the manual summary. Any component subset of the summary can be leaked. A route map and access list must be defined to source the leaked route.
The following default behavior occurs if the ip summary-address eigrp command is configured using the leak-map keyword and either the route map or access list is not configured:
•
•
Examples
The following example configures an administrative distance of 95 on Ethernet interface 0/0 for the 192.168.0.0/16 summary address:
Router(config)# router eigrp 1Router(config-router)# exitRouter(config)# interface Ethernet 0/0Router(config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.0.0 95The following example configures the 10.1.1.0/24 subnet to be leaked through the 10.0.0.0 summary address:
Router(config)# router eigrp 1Router(config-router)# exitRouter(config)# access-list 1 permit 10.1.1.0 0.0.0.255Router(config)# route-map LEAK-10-1-1 permit 10Router(config-route-map)# match ip address 1Router(config-route-map)# exitRouter(config)# interface Serial 0/0Router(config-if)# ip summary-address eigrp 1 10.0.0.0 255.0.0.0 leak-map LEAK-10-1-1Router(config-if)# endRelated Commands
auto-summary (EIGRP)
Configures automatic summarization of subnet routes to network-level routes (default behavior).
Feature Information for EIGRP Route Leaking
Table 1 lists the release history for this feature.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note
CCVP, the Cisco Logo, and the Cisco Square Bridge logo are trademarks of Cisco Systems, Inc.; Changing the Way We Work, Live, Play, and Learn is a service mark of Cisco Systems, Inc.; and Access Registrar, Aironet, BPX, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Enterprise/Solver, EtherChannel, EtherFast, EtherSwitch, Fast Step, Follow Me Browsing, FormShare, GigaDrive, GigaStack, HomeLink, Internet Quotient, IOS, IP/TV, iQ Expertise, the iQ logo, iQ Net Readiness Scorecard, iQuick Study, LightStream, Linksys, MeetingPlace, MGX, Networking Academy, Network Registrar, Packet, PIX, ProConnect, RateMUX, ScriptShare, SlideCast, SMARTnet, StackWise, The Fastest Way to Increase Your Internet Quotient, and TransPath are registered trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries.
All other trademarks mentioned in this document or Website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0609R)
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2006 Cisco Systems, Inc. All rights reserved.
