Gateway Redundancy

The Need for Gateway Redundancy

• Ideally there is more than one exit in your house or at any building!
  • "a backup solution"

First Hop Redundancy Protocols

• Hot Standby Routing Protocol (HSRP)

• Virtual Router Redundancy Protocol (VRRP)

• Gateway Load Balancing Protocol (GLBP)

• If your first hop goes away what can you get to?

  • Nothing.

Understanding FHRPs

• HSRP
  • Cisco
  • Load sharing
    • Active forwarder and an standby forwarder
• VRRP
  • Standard
  • Load sharing
• GLBP
  • Cisco
  • Load Balancing
    • Devices participating and talking at the same time

HSRP Example Topology

• There is two routers but they work as a team to present the illusion to the world of a separate virtual router "A".
• We give the virtual router which is the result of the effort of routers A and B a virtual MAC address associated with it.
• Down the road you may have a failure and the other device will come up and replace it.
  • When you see that the standby device will become active.

• Virtual IP and virtual MAC can be moved to either of the actual routers depending on which one is active on which one is standby
• VRRP does this very similarly

GLBP

• A device that is in control looks at the load on each router and delivers the ARP reply to talk to the gateway that has less load to it.
• Cisco proprietary

• We can take our VLANs and architect our network for load distribution using Spanning Tree Protocol (STP)
• By splitting them up half and half through Spanning Tree we can get efficient link utilization
• The upstream switches: (60 VLANs)
  • Master device to the top half (1-30)
  • Standby device to the bottom (31-60)
• This gives us load distribution.