When to Use First Hop Redundancy Protocols (FHRPs)

Clients like computers can only have ONE default gateway. If that one router crashes the computer is stuck, because his default gateway is unavailable.

Welcome to the reason we have first hop redundancy protocols:

• HSRP
  hot standby redundancy protocol
  cisco proprietary
• VRRP
  virtual router redundancy protocol
  industry standard
• GLBP
  gateway load balancing protocol
  cisco proprietary

All the protocols virtualize the ip address, instead of the router sitting there with the ip address .1 and .2, we could virtualize the .1 ip address and give the routers the .2 and .3 address. So now these routers will send HELLO messages to each other, if the active stops responding the passive one takes action. If the router .2 is currently active, it is responding for the .1 ip address. But there is one point to consider, you must virtualize the ip address, as well as the MAC address! To find its way the client sends an ARP message, the router responds with the MAC address, but it can’t be HIS mac address, it has to be a virtualized MAC address. Because the client caches the mac of the router, and if the router .2 dies, how should the client know how to reach the other router? It doesn’t because the MAC address stays the same cause its virtualized.

Flavors of FHRPs

Preemption means that if router 1 crashed and it failed over, without preemption enabled, it won’t failing back to router 1.

In VRRP you can actually assign the .1 ip address to a router so it automatically gets the master. If the master fails the .2 address still responds to the .1 address.

Question: can you load balance HSRP and VRRP?

Yes, but you have to do it with VLANs. For each virtual interface on a router, you have to choose this interface is the master or backup for that network and so on.

But that means, for every ARP request the clients sends like “hey I want to go to the internet, what is the mac address of the ip address .1?”
The AVG responds: “ it’s this one MAC-adress A”
Another client comes and asks “hey i want to go to the internet, what is the mac address of the ip address .1?”
The AVG responds: “it’s this one; MAC-address B”

And like this happens the load balancing for GLBP. You can adjust the algorithm, which means how much traffic goes over the AVG and the AVF.

Castle Rysen – Configuring HSRPv2

Steps to configure HRSP

1. Configure secondary internet connection + router
2. Convert to HRSP config
3. Test it baby!

IF you want to have a second internet connection, you might consider:

• It is good to go with a second carrier instead of just a second link
  if the carrier has problems you lose both lines.
• How is the physical conduit of this lines.
  Can you run this line on a separate conduit to our building?

Cisco IOS commands learned in this lesson

HSRP Configuration Commands (v1 & v2)

Command	Mode	Description
standby version 2	Interface Config	Enables HSRP Version 2 (supports IPv6, uses multicast 224.0.0.102).
standby <group> ip <virtual-ip>	Interface Config	Sets the virtual IP address shared by the client default gateways (e.g., .1).
standby <group> priority <value>	Interface Config	Sets router priority (Default is 100). Highest priority becomes ACTIVE.
standby <group> preempt	Interface Config	Forces a recovered higher-priority router to reclaim the ACTIVE role.
standby <group> track <interface>	Interface Config	Decrements priority if a tracked WAN/uplink interface goes down.
standby <group> name <group-name>	Interface Config	Assigns a custom text name to the HSRP redundancy group.

VRRP Configuration Commands

Used for Virtual Router Redundancy Protocol (Industry Standard).

Command	Mode	Description
vrrp <group> ip <virtual-ip>	Interface Config	Sets the virtual IP address. Can match the router’s physical IP address.
vrrp <group> priority <value>	Interface Config	Sets router priority (Default is 100). Highest priority becomes MASTER.
vrrp <group> preempt	Interface Config	Enabled by default in VRRP. Forces higher priority to take over as MASTER.
no vrrp <group> preempt	Interface Config	Disables preemption if you want to keep the current MASTER after failover.

GLBP Configuration Commands

Used for Gateway Load Balancing Protocol (Cisco Proprietary).

Command	Mode	Description
glbp <group> ip <virtual-ip>	Interface Config	Sets the virtual IP address. Elects the AVG (Active Virtual Gateway).
glbp <group> priority <value>	Interface Config	Sets priority for AVG election (Highest priority becomes AVG).
glbp <group> preempt	Interface Config	Enables preemption for the AVG role.
glbp <group> load-balancing <method>	Interface Config	Sets the algorithm (round-robin, weighted, or host-dependent).
glbp <group> weighting <value>	Interface Config	Assigns capacity weight for AVF (Active Virtual Forwarder) load distribution.

Verification & Testing Commands (Exec Mode)

Used during “Step 3: Test it baby!” to verify state, failover, ARP tables, and virtual MAC addresses.

Command	Privilege Mode	Description
show standby	Privileged EXEC	Displays full HSRP status, active/standby routers, timers, and virtual MACs.
show standby brief	Privileged EXEC	Summary view of HSRP state (Active, Standby, Local, group, virtual IP).
show vrrp / show vrrp brief	Privileged EXEC	Displays VRRP state, MASTER/BACKUP status, and virtual IP parameters.
show glbp / show glbp brief	Privileged EXEC	Displays GLBP state, AVG router, and AVF virtual MAC assignments.
show ip arp	Privileged EXEC	Checks the ARP cache for virtual IP-to-virtual MAC mappings on local interfaces.
show mac address-table	Privileged EXEC	Displays layer 2 forwarding table entries for virtual MAC addresses.

Troubleshooting & Debugging Commands

Used to observe real-time state changes, failovers, and hello messages between routers.

Command	Privilege Mode	Description
debug standby events	Privileged EXEC	Triggers real-time alerts for HSRP state changes (e.g., Standby to Active).
debug standby packets	Privileged EXEC	Monitors HELLO packet exchanges between HSRP peers.
debug vrrp	Privileged EXEC	Displays real-time VRRP state machine events and packet exchanges.
debug glbp	Privileged EXEC	Displays real-time GLBP AVG elections and AVF updates.
undebug all / un all	Privileged EXEC	Turns off all active debugging outputs.