09-10-2010, 05:22 PM
VIRTUAL ROUTER REDUNDANCY PROTOCOL
INTRODUCTION
The Explosive growth of the internet has resulted in a strategic shift in every organization’s communication needs. Internet connectivity is a minimal requirement for almost every organization. There are networks which an outage will cause collapse of a business or loss of considerable amount of money. Such networks are willing or have to invest into redundancy solutions. There are many ways of minimizing network outages and every alternative has its pros and cons. A better choice is to use the Virtual Router Redundancy Protocol (VRRP), which eliminates the single point of failure while maintaining a single router’s ease of administration. In the, network running VRRP all edge switches are “dualhomed.”
HARDWARE COMPONENTS
The basic hardware components of a network includes
• Transmission facilities
• Access devices
• Devices that repeat transmitted signals
Transmission Facilities
Transmission facilities are the media used to transport a network’s signals to their destinations. Media Types can include coaxial cables, twisted pair and optics cabling.
Access Devices
An access device is Responsible for formatting data so that it can be accepted in the network, placing that data on the network, accepting transmitted data that’s addressed to it. LAN the access device is network interface card. In WAN the access device is Router.
Routers operate at Layer 3 and include two types of protocol: Routable and Routing.
VIRTUAL ROUTER REDUNDANCY PROTOCOL
One option is simply to add a second router. This would provide redundancy, but also complicate device and address management. Typically, network managers configure hosts such as PCs and servers with a single static route – the default gateway. It is technically possible for hosts to use dynamic routing protocols, and doing so would allow hosts to recognize a secondary router upon the failure of the primary router. However, this option is difficult to manage and is seldom used in practice.
A better choice is to use the Virtual Router Redundancy Protocol (VRRP), which eliminates the single point of failure while maintaining a single router’s ease of administration. Let’s look at the same network running VRRP. In the figure below, all edge switches are now “dualhomed.” meaning each connects to two routers. As before, the original router normally forwards traffic, but now there is a backup router standing by. The primary router may fail, or the network may face the more common problem of the failure of a link to the primary router. Either way, VRRP helps ensure that the backup router will automatically take over forwarding responsibilities, with no interruption in connectivity.
FUNCTION OF VRRP
VRRP specifies an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. The VRRP router controlling the IP address (es) associated with a virtual router is called the Master, and forwards packets sent to these IP addresses. The election process provides dynamic fail over in the forwarding responsibility should be the Master become unavailable
Virtual Router Redundancy Protocol (VRRP) specifies an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. The VRRP router controlling the IP address (es) associated with a virtual router is called the Master, and forwards packets sent to these IP addresses.
The election process provides dynamic fail over over in the forwarding responsibility should be the Master become unavailable. This allows any of the virtual routers IP addresses on the LAN to be used as the default first hop router by end –hosts. The advantage of using VRRP is a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host. VRRP packets are sent encapsulated in IP packets.
Using VRRP, a virtual IP address can be specified manually or with Dynamic Host Configuration Protocol (DHCP) as a default. A virtual IP address is shared among the routers, with one designed as the master router and the others are backups. In case, the master fails, the virtual IP address is mapped to a backup router’s IP address. (This backup becomes the master router.) VRRP can also be used for load balancing. VRRP is part of both IPv 4 and IPv6.
The Virtual Router Redundancy Protocol (VRRP) transfers the responsibility of routing from one router to another if the original router goes down. In other words, it provides backup for a router connecting a network to the outside world.
Routers are smart machines that are capable of making routing decisions (assuming that some type of Dynamic Routing is enabled) if there are any changes in the topology. On the other hand, hosts cannot make routing decisions on their own, even if there are such changes.
Hosts have a default gateway router configured, and that router is the configured, and that router is the world. Hosts on one network can communicate with hosts on any other network, provided there is a route between them. Everything seems to work well as long as default gateway for the hosts on the LAN is up and running. But what happens if the default gateway goes down? All hosts that have this router configured as the default gateway lose connectivity to the outside world. There is a possibility that there is another router that has a connection to this LAN and to the rest of the network. Can this working router take the responsibilities of the router that went down?
It can, but only if you change the default gateway on the hosts. When a host needs to communicate with a host on a different LAN, it sends the information to the default gateway address. If that address is down, then the connection is lost. To transfer the responsibilities of this router to the working router, you need to point the traffic to the IP address of the working router. This means that you need to change the default gateway on the hosts and the connection will be resumed. You need to keep in mind that it will take a long time to reconfigure the default gateway on a large number of hosts.
When a router is defined as a static default gateway and no other dynamic routing protocol or router discovery protocol is used, the gateway becomes a critical point on the network. If that router fails, that critical link would be broken and the LAN would be disconnected from the other networks. The standard network consists of LAN, Router and WAN. If this router is down connection cannot be established between the LAN and WAN.