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Table Of Contents
Distributed GRE Tunneling Support
Prerequisites for Distributed GRE Tunneling Support
Restrictions for Distributed GRE Tunneling Support
Information About Distributed GRE Tunneling Support
How to Configure Distributed GRE Tunneling Support
Configuration Examples for Distributed GRE Tunneling Support
Distributed GRE Tunneling Support
This feature module describes the Distributed GRE Tunneling Support feature in Cisco IOS Release 12.2(14)S.
History for the Distributed GRE Tunneling Support Feature
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.
Contents
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Prerequisites for Distributed GRE Tunneling Support
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Prerequisites for Distributed GRE Tunneling Support
dCEF must be explicitly enabled on the router.
Restrictions for Distributed GRE Tunneling Support
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Information About Distributed GRE Tunneling Support
To implement distributed GRE tunneling support, you must understand the following concept:
Distributed GRE Tunnels
Distributed GRE Tunneling allows Cisco IOS software to switch packets into and out of the GRE tunnels using distributed Cisco Express Forwarding (dCEF). The tunneling is performed using recursive or "double" switching techniques that are currently deployed on existing nondistributed platforms. The relevant bits are ported into this development.
Double switching is performed by the handling of the received IP packet in the existing code path until it is determined that the packet needs encapsulation or de-encapsulation. Recursively forwarding the IP packet through the IP switching path again explains the "double" aspect of the switching.
The GRE tunneling allows service providers to support a large number of tunnels by forwarding distributed tunneled packets. This feature is an extension of the nondistributed forwarding information base (FIB) forwarding paths.
How to Configure Distributed GRE Tunneling Support
There are no tasks for the Distributed GRE Tunneling Support feature.
Note
Configuration Examples for Distributed GRE Tunneling Support
There are no configuration examples for the Distributed GRE Tunneling Support feature.
Note
Additional References
The following sections provide references related to Distributed GRE Tunneling Support.
Related Documents
dCEF configuration tasks
"Configuring Cisco Express Forwarding" chapter in the Cisco IOS Switching Services Configuration Guide, Release 12.2
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
RFC 1701
Generic Routing Encapsulation (GRE)
RFC 1702
Generic Routing Encapsulation over IPv4 Networks
1 Not all supported RFCs are listed.
Technical Assistance
Command Reference
None
Glossary
CEF—A mode of packet switching in Cisco IOS Software. Also known as FIB-switching.
Note
© 2005 Cisco Systems, Inc. All rights reserved.
