Networking Software (IOS & NX-OS)

Table Of Contents

Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

Finding Feature Information

Contents

Prerequisites for UDP Forwarding Support for IP Redundancy Virtual Router Groups

Information About UDP Forwarding Support for IP Redundancy Virtual Router Groups

Benefits of the UDP Forwarding Support for Virtual Router Groups Feature

How to Configure UDP Forwarding Support for IP Redundancy Virtual Router Groups

Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

Configuration Examples for UDP Forwarding Support for IP Redundancy Virtual Router Groups

Example: Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for UDP Forwarding Support for IP Redundancy Virtual Router Groups

Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

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First Published: February 10, 2008
Last Updated: January 25, 2011

User Datagram Protocol (UDP) forwarding is a feature used in Cisco IOS software to forward broadcast and multicast packets received for a specific IP address. Virtual Router Group (VRG) support, currently implemented with the Hot Standby Routing Protocol (HSRP), allows a set of routers to be grouped as a logical router that answers to a well-known IP address. The UDP Forwarding Support for IP Redundancy Virtual Router Groups feature enables UDP forwarding to be VRG aware; this results in packets getting forwarded only to the active router in the VRG.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for UDP Forwarding Support for IP Redundancy Virtual Router Groups" section.

Use Cisco Feature Navigator to find information about platform support and Cisco 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

•Information About UDP Forwarding Support for IP Redundancy Virtual Router Groups

•Prerequisites for UDP Forwarding Support for IP Redundancy Virtual Router Groups

•How to Configure UDP Forwarding Support for IP Redundancy Virtual Router Groups

•Configuration Examples for UDP Forwarding Support for IP Redundancy Virtual Router Groups

•Additional References

•Feature Information for UDP Forwarding Support for IP Redundancy Virtual Router Groups

Prerequisites for UDP Forwarding Support for IP Redundancy Virtual Router Groups

The UDP Forwarding Support for Virtual Router Groups feature is available only on platforms that support VRGs.

Information About UDP Forwarding Support for IP Redundancy Virtual Router Groups

•Benefits of the UDP Forwarding Support for Virtual Router Groups Feature

Benefits of the UDP Forwarding Support for Virtual Router Groups Feature

Forwarding is limited to the active router in the VRG instead of all routers within the VRG. Prior to the implementation of this feature, the only VRG support was HSRP. Within a VRG that is formed by HSRP, the forwarding of UDP-based broadcast and multicast packets is done by all the routers within the VRG. This process can cause some DHCP servers to operate incorrectly. By making the UDP forwarding code VRG aware, forwarding will be limited to the active router in the VRG.

VRG awareness is achieved with IP Redundancy Service (IRS). The IRS API provides notification updates of a specific VRG, addition and deletion of a VRG, and querying of the current state of a VRG. A state change notification is provided to avoid the performance impact of querying the state of the VRG each time it is needed. The UDP forwarding code caches the VRG state for each required helper address that is defined. Each time the UDP forwarding code needs to execute, it checks the current state of the VRG associated with the helper address and forwards packets only to VRGs that are active.

How to Configure UDP Forwarding Support for IP Redundancy Virtual Router Groups

•Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. no shutdown

5. ip address ip-address mask

6. ip helper-address address redundancy vrg-name

7. standby group-number ip ip-address

8. standby group-number name group-name

9. end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface fastethernet 0/0	Specifies an interface and enters interface configuration mode.
Step 4	no shutdown Example: Router(config-if)# no shutdown	Restarts a disabled interface.
Step 5	ip address ip-address mask Example: Router(config-if)# ip address 172.16.10.1 255.255.255.0	Sets a primary address for the interface.
Step 6	ip helper-address address redundancy vrg-name Example: Router(config-if)# ip helper-address 10.1.1.1 redundancy shop	Enables UDP forwarding support for the VRG.
Step 7	standby group-number ip ip-address Example: Router(config-if)# standby 1 ip 172.16.10.254	Activates HSRP.
Step 8	standby group-number name group-name Example: Router(config-if)# standby 1 name shop	Configures the name of the standby group.
Step 9	end Example: Router(config-if)# end	Exits the current configuration mode and returns to privileged EXEC mode.

Configuration Examples for UDP Forwarding Support for IP Redundancy Virtual Router Groups

•Example: Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

Example: Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups

The following example shows how to configure UDP Forwarding Support for IP Redundancy Virtual Router Groups:

Router(config)# interface fastethernet 0/0

Router(config-if)# no shutdown

Router(config-if)# ip address 172.16.10.1 255.255.255.0

Router(config-if)# ip helper-address 10.1.1.1 redundancy shop

Router(config-if)# standby 1 ip 172.16.10.254

Router(config-if)# standby 1 name shop

Router(config-if)# end

Additional References

Related Documents

Related Topic	Document Title
IP application services commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples	Cisco IOS IP Application Services Command Reference

Standards

Standard	Title
No new or modified standards are supported, and support for existing standards has not been modified	—

MIBs

MIB	MIBs Link
No new or modified MIBs are supported, and support for existing MIBs has not been modified	To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFC	Title
No new or modified RFCs are supported, and support for existing RFCs has not been modified	—

Technical Assistance

Description	Link
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.	http://www.cisco.com/cisco/web/support/index.html

Feature Information for UDP Forwarding Support for IP Redundancy Virtual Router Groups

Table 1 lists the features in this module.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which 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.

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Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

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Table 1 Feature Information for UDP Forwarding Support for IP Redundancy Virtual Router Groups

Feature Name	Releases	Feature Information
UDP Forwarding Support for IP Redundancy Virtual Router Group	Cisco IOS XE 3.1.0SG 12.2(15)T	User Datagram Protocol (UDP) forwarding is a feature used in Cisco IOS software to forward broadcast and multicast packets received for a specific IP address. Virtual Router Group (VRG) support is currently implemented with the Hot Standby Routing Protocol (HSRP) and it allows a set of routers to be grouped as a logical router that answers to a well known well-known IP address. The UDP Forwarding Support for IP Redundancy Virtual Router Groups feature enables UDP forwarding to be VRG aware, resulting in forwarding only to the active router in the VRG. The following command was introduced or modified: ip helper-address.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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