HSRP OperationĪ large class of legacy host implementations that don't support dynamic discovery are capable of configuring a default router. There is no mechanism for switching to an alternative router if the default gateway fails. This configuration information typically comprises an IP address and a default gateway. A host that runs a DHCP client requests configuration information from a DHCP server when it boots onto the network. Dynamic Host Configuration Protocolĭynamic Host Configuration Protocol (DHCP) ( RFC 1531) provides a mechanism for passing configuration information to hosts on a TCP/IP network. The default advertisement rate is once every 7 to 10 minutes, and the default lifetime is 30 minutes. The default timer values of IRDP mean that it's not suitable for detection of failure of the first hop. A host that runs IRDP listens for hello multicast messages from its configured router and uses an alternate router when it no longer receives those hello messages. Some newer IP hosts use ICMP Router Discovery Protocol (IRDP) ( RFC 1256) to find a new router when a route becomes unavailable. Running a dynamic routing protocol on every host may not be feasible for a number of reasons, including administrative overhead, processing overhead, security issues, or lack of a protocol implementation for some platforms. The drawback of using RIP is that it is slow to adapt to changes in the topology. Some IP hosts run (or snoop) a dynamic routing protocol such as the Routing Information Protocol (RIP) or Open Shortest Path First (OSPF) to discover routers. In either case, for a significant period of time, the host can't communicate with the remote host, even though the routing protocol has converged, and Router B is prepared to transfer packets that would otherwise go through Router A.
#HSRP CISCO MAC ADDRESS MAC#
You can either wait for ARP to acquire the MAC address of another router, Router B, on the local segment by sending another ARP request, or reboot the host to force it to send an ARP request. If Router A fails, the host continues to send packets destined for the remote host to the MAC address of Router A even though those packets have nowhere to go and are lost. With proxy ARP, the host behaves as if the remote host were connected to the same segment of the network. A router, Router A, on the network replies on behalf of the remote host and provides its own MAC address. When a host runs proxy ARP, it sends an ARP request for the IP address of the remote host it wants to contact. Some IP hosts use proxy Address Resolution Protocol (ARP) to select a router. In addition to what is listed below, it is important to note that many hosts only allow you to configure a default-gateway. This may be because the protocol wasn't initially intended to provide network resiliency or because it isn't feasible for every host on a network to be running the protocol. Many of these mechanisms don't provide the network resiliency required by network administrators. Dynamic Router Discovery Mechanismsīelow are descriptions of dynamic router discovery mechanisms that are available to hosts. Hosts continue to forward IP packets to a consistent IP and MAC address, and the changeover of devices doing the routing is transparent. This way, one router can assume the routing responsibility of another, should it go out of commission for either planned or unplanned reasons. The members of the virtual router group continually exchange status messages. One way to achieve near-100 percent network uptime is to use HSRP, which provides network redundancy for IP networks, ensuring that user traffic immediately and transparently recovers from first hop failures in network edge devices or access circuits.īy sharing an IP address and a MAC (Layer 2) address, two or more routers can act as a single "virtual" router. Conventionsįor more information on document conventions, refer to Cisco Technical Tips Conventions.
#HSRP CISCO MAC ADDRESS SOFTWARE#
This document is not restricted to specific software and hardware versions. There are no specific requirements for this document. This document describes the features and functionality of Hot Standby Router Protocol (HSRP).
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