How does hsrp link its virtual ip to mac address bindings

In a further aspect, operation c is periodically repeated. In yet a further aspect, operations a and b are repeated for a plurality of received pairs of a request and a response that each include an internet protocol IP address and a media access control MAC address for a particular node, and a plurality of binding entries are received into the first network device from the second network device, wherein the received binding entries include pairs of corresponding IP and MAC addresses for particular nodes and interface information for the particular nodes.

At the first network device, each received binding entry is also stored in the DHCP Snooping Database along with an indication that the each received binding entry was not locally learned. Similarly binding entries learned on the first network device may be received into the second network device from the first network device. At the second network device too, each received binding entries may also be stored in the DHCP Snooping Database along with an indication that each received binding entry was not locally learned.

In another implementation, the first network device is in a different chassis than the second network device. In another aspect, operation c is repeated for a plurality of other network devices that belong to the same redundancy group as the first network device. In yet another implementation, operation c is triggered by the first network device receiving a request for DHCP binding entries from the second network device. In another embodiment, the invention pertains to a computer system is operable to facilitate DHCP dynamic host configuration protocol Snooping data.

The computer system includes one or more processors and one or more memory. The one or more processors and memory are configured for performing any combination of the above described method operations. These and other features of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention. Reference will now be made in detail to a specific embodiment of the invention. An example of this embodiment is illustrated in the accompanying drawings.

While the invention will be described in conjunction with this specific embodiment, it will be understood that it is not intended to limit the invention to one embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details.

In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. However, embodiments of the present invention may be implemented using any suitable redundant router protocol, besides HSRP. In general, the present invention provides techniques for facilitating the use of DHCP dynamic host configuration protocol binding data in a redundant router group, where the routers may reside in separate boxes or chassis.

The redundant router group may include any suitable number and type of routers configured to communicate with each other and provide backup for the group while also providing routing capabilities for a plurality of hosts in the same or different virtual local area networks VLAN's. In this arrangement, the distribution layer includes two or more distribution routers A plurality of hosts are coupled through access switches to each of the two or more distribution routers The distribution routers form a redundancy group and this redundancy group may be utilized by one or more VLAN's.

Each router may also have a plurality of interfaces, and each interface may support one or more VLAN's.

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When a router in the redundancy router group fails, another router in such group takes over for the failed router. In the illustrated example, router a is currently active for VLAN 1 devices, and router b serves as a standby for these VLAN 1 devices when router a fails. Each DHCP Snooping Database may include one or more physical storage devices that are located at the same location or different physical locations. Embodiments of the present invention provide mechanisms for sharing DHCP information between routers in a redundancy group.

The particular router then receives a response containing the IP address for the particular MAC address in operation The request for an IP address may be for the requesting node or another node. In alternative embodiments, a request may be made for a MAC address for a particular IP address with respect to a particular host.

How to configure Hot Standby Router Protocol (HSRP) with Cisco routers

In one example, host a of FIG. This response is seen by router a as it is sent from the DHCP Server to the requesting host a. The binding between the IP address and corresponding MAC address is then stored in a DHCP Snooping Database along with interface information and a status field indicating whether the binding was locally learned in operation Each database entry includes an IP address field , a corresponding MAC address field , an interface identifier , an indicator as to whether the binding was locally learned, and an age field As shown in FIG.

Likewise in FIG. Referring FIG.

The exporting of DHCP Snooping binding information may be initiated by either the sending or the receiving router. In an alternative implementation, when a switchover is occurring or imminent, the binding information is sent once by the failing router or grabbed by the router that is taking over the active role. However, the former embodiment of periodically sending this binding information prior to a switchover will likely be more reliable since each router in the redundancy group is more likely to obtain the necessary DHCP binding information in periodic updates prior to complete shut down of the failing router.

The locally learned binding data may be sent from a first router to one or more peer routers using any suitable mechanism. For example, each router can be configured with the each peer router address, or multicasting can be set up for a router group so that they learn about their peers. As each router in a redundancy group comes up, it is configured as belonging to the particular redundancy group and informs the routers around it that it belongs to such group. Then the routers in the same redundancy group exchange information to determine which is active, etc. Since each active router is sending its locally learned binding information to its peers, each received set of binding and corresponding interface information is stored, along with an indication that such binding were not locally learned, in operation As shown, each binding entry may also have an age field This age field may be used to determine whether the binding has timed out or been relinquished by the corresponding host.

In one implementation, the age field indicates the amount of time that has passed since the last response from the corresponding host. In this example, a binding entry is determined to be timed out when the time is greater than a predefined value. In another implementation, the age field may indicate a timer value that is updated with each corresponding host response.

In this case, the binding is aged out when the timer has timed out. The above described mechanisms for maintaining a DHCP database in each router of a redundancy group works for routers that have separate boxes and do not have the use of backplane signals for communicating state information.

In the simplest implementation, the active router simply sends a custom packet to inform the one or more standby router s in its peer group about updates to its DHCP Snooping database. One example of such a packet but not limited to would be UDP. Hot Standby Router Protocol HSRP , a proprietary protocol developed by Cisco , allows to decouple the IP addresses from the physical interfaces and to associate them to groups of interfaces, providing hardware redundancy.

Technically speaking, HSRP sends its hello message to the multicast address We are going to see how to mirror a business gateway to assure Internet access even in case of failure of the primary router. We can check the configuration of the HSRP group with the show standby command. It allows multiple routers to be deployed in hot standby mode to eliminate network interruption caused by a single device failure. To achieve HSRP, two or more routers on a network form a hot standby group, which is a virtual router. If a router has a higher priority than all other routers, the router becomes the active router in the corresponding standby group.

When Hello messages sent from the active router fail to be received within the hold time, the standby router with the highest priority becomes the active router.

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None of the hosts on the network detects the packets exchanged between routers. The destination IP address is the multicast IP address The first replacement method is not commonly used because service is interrupted for about 3 seconds during Step 3. Therefore, you are advised to use the second replacement method. In Figure , Cisco switches are deployed. Two core switches constitute a stack. Two aggregation switches establish an Eth-Trunk in manual load balancing mode, and also establish OSPF neighbor relationships with core switches to receive and transmit routes.

HSRP is used to implement virtual gateway backup. CiscoA is the master gateway and CiscoB is the backup gateway. Huawei switches are used to replace two aggregation switches in the networking without changing the original network planning. Configure link aggregation in manual load balancing mode between Huawei switches to load balance traffic. Configure Huawei switches to achieve interworking with other Cisco switches to prevent loops.

Configure service forwarding functions for the Huawei switches by following the original network planning.

S2700, S3700, S5700, S6700, S7700, and S9700 Series Switches Typical Configuration Examples

Processes the IP packets destined for the virtual IP address if the device is the IP address owner, and discards them if it is not. Becomes the backup if the device receives a VRRP Advertisement packet with the same priority as its VRRP priority and the IP address of the local interface is smaller than that of the connected interface on the remote device. Receives VRRP Advertisement packets from the master and determines whether the master is working properly.

Processes the IP packets destined for the virtual IP address based on the Layer 2 forwarding process. If the backup does not receive Advertisement packets after the timer expires, the backup becomes the master. The calculation formula is as follows: Devices in a VRRP group select the master based on their priorities. If the master fails, the backup with the highest priority becomes the new master.

If the original master is replaced by another device in the group, the new master sends gratuitous ARP packets carrying the virtual MAC address and virtual IP address of the virtual router. The new master uses these packets to update the MAC address entry on the connected network devices or hosts. User traffic is then switched to the new master. This process is transparent to users. When the original master recovers and is the IP address owner with priority , the original master reverts to the Master state.

If the priority of the original master is smaller than , the device switches to the Backup state. The priority of the device is then restored to its original value before the failure. HSRP uses the priority to determine the active router.

Secondary IP addresses and HSRP

The HSRP priority can be set manually. Basic Concepts Standby group: Active router: Standby router: Hello Time: If the value is not specified, the Hello time depends on the interval when the active router successfully sends two Hello messages.

Otherwise, the default value 3s is used. Hold Time: If the routers have the same priority, the router with the largest IP address becomes the active router. Vendor ID: HSRP code: HSRP group number: In this example, 2f is a hexadecimal value, which equals to the decimal value This message indicates that the active router does not want to be the active router again.


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