As Andres says, gratuitous arp will take care of this situation. Here's the info from the documentation: http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_hsrp_ps6441_TSD_Products_Configuration_Guide_Chapter.html HSRP Gratuitous ARP
The HSRP Gratuitous ARP feature configures HSRP to check that the entries in the ARP cache are correct and to send periodic gratuitous ARP packets from one or more HSRP active groups. By default, HSRP sends out three gratuitous ARP packets from an HSRP group when the group state changes to Active. HSRP sends the first gratuitous ARP packet when the group becomes active. The second two gratuitous ARP packets are sent 2 and 4 seconds later. The HSRP Gratuitous ARP feature enhances the capability of HSRP so that the number and frequency of gratuitous ARP packets sent by an active HSRP group are configurable. Use the *standby arp gratuitous* command in interface configuration mode to configure a specific number of gratuitous ARP packets to be sent at a specified interval. Use the *standby send arp *command in EXEC mode to configure HSRP to send a single gratuitous ARP packet for each active group. When the *standby send arp* command is configured, HSRP checks that the entries in the ARP cache are correct prior to sending a gratuitous ARP packet. If an ARP entry is incorrect, HSRP will try to re-add it. Static or alias ARP entries cannot be overwritten by HSRP. Configuring the *standby send arp *command ensures that a host ARP cache is updated prior to heavy CPU-usage processes or configurations are started. When CPU usage is above 50% due to heavy ARP traffic combined with moderate software switched IP traffic, ARP refresh requests could fail, causing some application servers to lose their default gateway ARP entries and fail to communicate with the rest of the network. In some scenarios, operations such as enabling a large access list, can cause ARP requests from hosts to be delayed, causing the host to have no default gateway for a short time. A periodic gratuitous ARP packet sent from the HSRP active router refreshes the host ARP cache before it expires. -Dave On Tue, Jan 25, 2011 at 12:03 PM, Nilesh Mehta <[email protected]> wrote: > Whta is the configuration on routers/Switches ? > Lets say router A: > Int Fa0/0 > standby 1 ip 10.10.10.1 > Standby 1 priority 110 > standby 1 preempt > -------------------------- > Router B: > int fa0/0 > > standby 1 ip 10.10.10.1 > standby 1 preempt > > Switch A & B configured with > > ip defualt-gateway 10.10.10.1 > > and if you have proper cabling done with both routers > then layer 2 switches should be able to pass > traffic to active/standby routers wiht out any problem ? > I think it should work with this configuration. > Please correct me if I misunderstood anything > > Thanks > > Nilesh > On Mon, Jan 24, 2011 at 11:09 PM, Andres Villalva <[email protected] > >wrote: > > > Hi Nitin, > > > > The switch itself doesn't know. It only knows what mac address is > connected > > to it. Hsrp uses gratuitous arp to rewrite the existing mac address in > the > > arp table with the mac address of the standby router (which is about to > > become the active router). > > > > Hope that helps, > > > > Andres > > > > On 25/01/2011 4:19 PM, "Nitin Kumar" <[email protected]> wrote: > > > > Dear All, > > > > I have slight confusion on working of HSRP for redundant gateway. I have > > two access-switch/stack connected to both HSRP active and standby > routers. > > All access switches are sending traffic to HSRP active gateway. But if > for > > some reason HSRP state changes on Active gateway and standby becomes > > active... > > > > How does Access switches know when HSRP gateway has changed from active > to > > standby and they need to send traffic over other link. > > > > Regards > > Nitin > > _______________________________________________ > > For more information regarding industry leading CCIE Lab training, please > > visit www.ipexpert.com > > _______________________________________________ > > For more information regarding industry leading CCIE Lab training, please > > visit www.ipexpert.com > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
