12/10/2023 0 Comments 8 minute timer high resolution .pngIf the active router fails, the standby router takes over as the active router. Additional routers in the HSRP group remain in the Listen state. In order to minimize network traffic, only the active and the standby routers send periodic HSRP messages after the protocol has completed the election process. Although an arbitrary number of routers can run HSRP, only the active router forwards the packets that are sent to the virtual router IP address. If the active router fails, the standby assumes the packet forwarding duties. Another router is elected as the standby router. This router is known as the active router. A single router that is elected from the group is responsible to forward the packets that hosts send to the virtual router. This set of routers is known as an HSRP group or standby group. Basic OperationĪ set of routers that run HSRP works in concert to present the illusion of a single default gateway router to the hosts on the LAN. The system only selects an additional configured default gateway at boot time if the first configured default gateway is determined unreachable by Internet Control Management Protocol (ICMP). The OS only uses one single default gateway at a time. But the multiple default gateways are not dynamic. Note: You can configure host workstations that run Microsoft OS for multiple default gateways. The changeover of devices that do the routing is transparent to the end workstations. Hosts are configured with a single default gateway and continue to forward IP packets to a consistent IP and MAC address. One router can assume the routing responsibility of another if a router goes out of commission for either planned or unplanned reasons. With HSRP, members of the virtual router group continually exchange status messages. This address is known as a default gateway. Most host workstations do not contain routing tables and use only a single next hop IP and MAC address. The address is necessary for host workstation default gateway redundancy. Two or more routers can act as a single, virtual router if they share an IP address and a MAC (Layer 2 ) address. HSRP, which is unique to Cisco platforms, provides network redundancy for IP networks in a manner that ensures that user traffic immediately and transparently recovers from first-hop failures in network edge devices or access circuits. Customers can satisfy their demands for near-100 percent network uptime if they leverage the HSRP in Cisco IOS® Software. This document is not intended to be a design guide, software-recommendation document, or a best practices document.īusinesses and consumers that rely on intranet and Internet services for their mission-critical communications require and expect their networks and applications to be continuously available to them. Nevertheless, the sole purpose of this document is to facilitate and guide engineers on who to troubleshoot HSRP. The document contains many references to software versions and network topology design. Note: This document details how to troubleshoot HSRP in Catalyst switch environments. Switch error messages that relate to HSRPĮxcessive network unicast flooding to the HSRP configuration Router report of a duplicate HSRP standby IP addressĬonstant HSRP state changes (active, standby, speak) This document covers these most-common issues that relate to HSRP: If your network is live, ensure that you understand the potential impact of any command. All of the devices used in this document started with a cleared (default) configuration. The information in this document was created from the devices in a specific lab environment. This document is not restricted to specific software and hardware versions. There are no specific requirements for this document. This document describes common issues and ways to troubleshoot Hot Standby Router Protocol (HSRP) problems.
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