Configuring UDP Forwarding Support for IP Redundancy Virtual Router Groups
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Configuring UDP Forwarding Support for IP Redundancy Virtual Router GroupsLast Updated: November 16, 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, 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 forwarde only to the active router in the VRG. This module explains the concepts related UDP forwarding and VRG support and describes how to configure UDP forwarding support for IP Redundancy Virtual Router Groups in a network.
Finding Feature InformationYour 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 Table at the end of this document. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Information About UDP Forwarding Support for IP Redundancy Virtual Router GroupsBenefits of the UDP Forwarding Support for Virtual Router Groups FeatureForwarding 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. The UDP Forwarding Support for VRGs feature limits forwarding to the active router in the VRG. VRG awareness is achieved with IP Redundancy Service (IRS). The IRS application programming interface (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 GroupsConfiguring UDP Forwarding Support for IP Redundancy Virtual Router GroupsSUMMARY STEPS
DETAILED STEPS Configuration Examples for UDP Forwarding Support for IP Redundancy Virtual Router GroupsExample: Configuring UDP Forwarding Support for IP Redundancy Virtual Router GroupsThe 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 vrg1 Router(config-if)# standby 1 ip 172.16.10.254 Router(config-if)# standby 1 name vrg1 Router(config-if)# end Additional ReferencesRelated DocumentsMIBsTechnical Assistance
Feature Information for UDP Forwarding Support for IP Redundancy Virtual Router GroupsThe following table provides release information about the feature or features described in this module. This table 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. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned 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. (1110R) 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. © 2011 Cisco Systems, Inc. All rights reserved.
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