First Hop Redundancy Protocols

Done

With this feature a network can have two or more routers in case the active one fails, allowing for redundancy.

Routers using these protocols will both share a virtual IP Address and a virtual MAC Address (each FHRP uses a different format for the virtual MAC).

Also, once the current active router fails, the standby router will send Gratuitous ARP. These are ARP reply without ARP requests, so the switches in the network can update their outgoing interfaces for a given MAC Address. Usually an ARP Reply is a Unicast, but in a Gratuitous ARP, it will be broadcast.

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FHRP are “non-preemptive”. It is similar to OSPF DR/BDR, the current roles will not change until something fails or reloads, by default. This can be changed by settings.

HSRP (Hot Standby Router Protocol)

Cisco proprietary

An active and standby router are elected

There are two versions:
- Version 1
- Version 2
  - This version adds support for IPv6 and increases the number of groups that can be configured.

Multicast IPv4 Address: v1 = 224.0.0.2 v2 = 224.0.0.102

virtual MAC Addresses: v1 = 0000.0c07.acXX (XX = HSRP group number) v2 = 0000.0c9f.fXXX (XXX = HSRP group number)

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IMPORANT: The MAC Address is a hexadecimal number, so the same applies for the group number. For example, it is possible to use the group number 200 in version 1 of HSRP, because it is equal to c8 in hexadecimal.

In a situation with multiple subnets/VLANs, you can assign a different active and standby router for each subnet/VLAN to load balance.

VRRP (Virtual Router Redundancy Protocol)

Open standard

A master and a backup are elected

Multicast IPv4 address: 224.0.0.18

Virtual MAC Address 0000.5e00.01XX (XX = VRRP group number)

GLBP (Gateway Load Balance Protocol)

Cisco proprietary

Load balances between multiple routers in the same subnet

An AVG (Active Virtual Gateway) is elected

Up to four AVFs (Active Virtual Forwarders) are assigned by the AVG (the AVG itself can be an AVF, too)

The AVG in a GLBP group assigns a virtual MAC address to the AVFs. When the AVG receives ARP requests that are sent to the virtual IP address for the GLBP group, the AVG responds with different virtual MAC addresses. This provides load balancing, because each of the primary AVFs will participate by forwarding a portion of the traffic sent to the virtual IP Address.

Multicast IPv4 Address: 224.0.0.102 (the same as HSRPv2)

Virtual MAC Address: 0007.b400.XXYY (XX = GLBP group number, YY = AVF number)

Configure HSRP

configure terminal
interface g0/0
standby {group-number} ip {virtual-ip}

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IMPORTANT: The group-number MUST match between the routers

Choose which router will be the Active

configure terminal
interface g0/0
standby {group-number} priority {0-255}

In order, the active router will be the one with:

Higher Priority (default 100)

Higher IP Address

Enable preemptive behavior

Enabling this will make the right active router take the lead even if another router has the active role. This is used in case the main router comes back up online.

configure terminal
interface g0/0
standby {group-number} preempt

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IMPORTANT: For it to take the role of active router it MUST have a higher priority or IP Address.

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NOTE: You can only enable it on the router you want to be active

Change HSRP version

configure terminal
interface g0/0    //interface configuration mode
standby version {1 | 2}

Verify HSRP

show standby