Rtr 1 has the highest priority so will it become the forwarding router again? The answer to that question depends on the preempt command. In short, for an FHRP router to take over from a currently-forwarding router, two parameters need to be True:. When a router first comes up, it does not have a complete routing table. Consequently, if that router preempts immediately, it will become the forwarding router immediately but with an incomplete routing table, so packets will be dropped.
The solution to this problem is to configure a delay on the preempt command so that the router that has just come up will wait a number of seconds before taking over from the currently forwarding router:. In figure 7 above, Rtr2 is currently the Active router. A second delay is typically more than enough time for an Interior Gateway Protocol to build the routing table so Rtr 1 will forward IP packets as soon as it becomes the Active router.
Then, no longer will packets drop when a new forwarding router takes over from a currently forwarding router. This means that for multiple routers inside a network, there is a framework readily established by HSRP to make a default gateway, in the event that the main gateway inadvertently becomes inaccessible.
It acts as a fail-safe, to put it in simple terms. This ensures a sustained connectivity even if certain problems are encountered. It was actually in when Cisco created a redundancy router protocol for its own use. This also utilizes a default hello countdown timer for 3 seconds, along with a hold timer that spans for 10 seconds. This protocol is said to work for a wide range of systems.
It even boasts of a faster timer of 1 second for its default hello, and a 3-second hold timer as well. In regards to VRRP, there is a backup router that supports the role of the master router, in the event that the latter fails to function. Spotlight Award Nomination. Content for Community-Ad. Follow our Social Media Channels.
RFC Separate IP Address needed for the Virtual. One Master, One Standby, all others are listening. One Master, all other routers are backup. More familiar to most network engineers. Can track an interface for failover depending on operating system and version, it can also track the reachability of an IP address. All HSRP routers use multicast hello packets to When applying multicast services such as video-on-demand, multimedia conferences and other heavy traffic, and the data generated by the network itself, it will cause local network "traffic jam" at a certain moment, and even become an incentive for the formation of multicast storms.
In the network shown in Figure 2, a large amount of application data traffic in the network preempts the bandwidth on the link, which increases the processing pressure of the core switch and prevents the trunk port from forwarding VRRP packets and BPDU packets in time, which results in the Switch -A does not receive the BPDU packet of Switch-B the forwarding delay is 15 seconds , and the switch port of Switch-A enters the learning and forwarding state from the blocked state.
After the multicast reaches the access layer switch, the access layer switch forwards it to Switch-B. After receiving this multicast, Switch-B forwards it to Switch-A through the interconnection port, forming a loop. Therefore, the normal link bandwidth is a guarantee for the normal VRRP network.
If this time is extended, the VRRP broadcast volume of each port will be reduced exponentially. However, due to the extension of the VRRP announcement interval, the time for the master-slave switchover in the VRRP network will be longer, and it is more difficult for the core switch to detect changes in the topology of the network.
Therefore, it is not possible to extend this time blindly, but to make appropriate adjustments according to the actual situation of the network. Ensure the status of the root switch and the master routing switch until the network topology changes. Figure 2. The process of forming a multicast storm. Access layer switches use port redundancy. Cisco, Avaya, 3Com, and other manufacturers have access port switches that have port redundancy, or elastic link features: on the port of the switch, through the manufacturer Proprietary technology to achieve failover on hardware.
When the main link is interrupted, the backup link will switch to the working state within 1 to 5 seconds. This technique does not require the operation of the spanning tree protocol, no BPDU overhead, and the switching time is much lower than the convergence time of the spanning tree the default convergence time of the spanning tree is 50 seconds, and with the complexity of the network topology, The convergence time will also increase.
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