From the course: CompTIA Network+ (N10-009) Cert Prep

First hop redundancy protocol (FHRP)

From the course: CompTIA Network+ (N10-009) Cert Prep

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First hop redundancy protocol (FHRP)

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- Let's say you are working on an important assignment and accessing content on the web, when all of a sudden, access to the internet goes away. Of course, you try everything you can to get reconnected, but to no avail. So you check the physical hardware, after all you work in IT, right? You should be able to do that, and you find that the gateway router has failed. The remedy for this problem is to replace the network card in the router, or maybe even replace the router altogether. Well, let's hope you have the card you need, or at least a spare router, because otherwise, you're not really going to be up anytime soon. It's not really going to be likely you've got the hardware just hanging around. Wouldn't it be wonderful though if the gateway router would automagically fix itself and keep access to the internet available even when there's a failure? Well, it might be asking too much for automatic repairs, but there is a way to provide seemingly uninterrupted network service through the use of what we call first hop redundancy protocol, otherwise known as FHRP. FHRP provides a failover redundant virtual gateway that is activated when the primary gateway router fails. By the way, it's called first hop because on any network, the first hop is going to be the router. It's going to be your default gateway. So packets headed out to the internet on the web come to that gateway or edge router in order to leave the network. And redundancy refers to a configuration in which two or more routers can serve as a backup to each other and be activated when needed. In a fairly common configuration, only a single gateway router connects to the internal network and to a WAN or to the internet. Sometimes it looks a little like this. An FHRP implementation though looks something like this. Two or more gateway routers with associated standby routers, each of which is configured with a unique IP address. All routers in an FHRP set are assigned the same virtual IP address and a virtual MAC address. The virtual IP address serves as the default gateway address for all of the devices on that network segment. One of the routers is designated as the default and the others are backups. Something that looks a little like this. FHRP is a failover protocol. When the active gateway router is operating, all network traffic is forwarded to the default gateway address, which is the virtual IP address. If it fails, the standby router, which has the same virtual IP assigned, begins servicing that network traffic. In FHRP, it takes care of designating one router as the active gateway versus the other standbys as peers. FHRP is implemented in one of these different option modes. There's going to be three of 'em. Hot standby router protocol, otherwise known as HSRP, VRRP, or what we call virtual router redundancy protocol, or GLBP, gateway load balancing protocol. Let's take a look at each one of these solutions. HSRP is a proprietary router redundancy protocol by Cisco Systems, and it operates essentially, as I've described, with the functions of FHRP. However, HSRP and the other FHRP protocol uses IP addresses, the virtual IPs. Each one of the routers in the group are assigned the same virtual IP, which has all the properties of a public IP address. The virtual IP address is configured to the node in a gateway router group as the address of the default gateway. That's what everybody is going to be using on that segment. Now, when we're talking about VRRP, the virtual router redundancy protocol, that's going to be a little bit different. It's vendor neutral, a vendor neutral redundancy protocol that groups a cluster of physical routers, which is going to be two or more, to produce a new single virtual router. It enables redundancy by assigning the same virtual gateway IP address and MAC address on all physical routers within the VRRP group. VRRP has almost the same operating function as HSRP. The major difference is that VRRP by default performs the process used to select the master router and the backup router or routers. This feature is preemption. On VRRP systems, preemption is enabled by default. On HSRP, preemption must be manually configured. VRRP assigns two states to routers, master and a backup. A master router is the current default gateway. The third FHRP protocol is going to be GLBP, otherwise known as gateway load balancing protocol, and it differs from the other two FHRP protocols that we've talked about. GLBP is another Cisco proprietary, first hop redundancy protocol that expands on the other FHRP protocols with a load balancing capacity, so it's going to be a different capability that's thrown in there. A priority weight is assigned to each of the gateway router groups. This weighting is used to balance the processing load of the routers. ARP request return MAC addresses that point to the weighted rotation of the active router in the gateway router group. However, this load balancing process doesn't assign routers based on the volume of traffic coming to the gateway, but rather it's based on the number of nodes associated with each gateway router group. So in a group of routers, in a virtual router JLBP selects an active virtual gateway. That's going to be the main one. The other routers in the group, they're all backups. If there are two or more backup routers, the router with the next highest priority is set to a standby state, and the others are put into a listening state. The virtual Mac address assigned to each one of the virtual routers in the group are assigned by the AVG. By default, GLBP routers are configured with a local multicast IPv4 address of 224.0.0.102. This is the address used to send hello packets to peers every three seconds on UDP Port 3222.

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