Category: FHRP

FHRPs: GLBP

GLBP is also Cisco Proprietary just like HSRP, the difference between GLBP and HSRP/VRRP is that it adds load balancing features in addition to the router redundancy.  Hosts will still point to a default gateway IP address, but GLBP will cause that traffic to be forwarded to one of up to four routers i na GLBP group.

GLBP has an Active Virtual Gateway (AVG) that assignes each router in the GLBP group a virtual MAC address, using the format: 0007.b400.XXYY where XX is the GLBP group and YY is a different number for each router (01,02,03 or 04)

When a client ARPs for the virtual IP address of the default gateway, GLBP AVG replies with one of the four possible routers in the group with their Virtual MAC address.  By doing so in a round robin fashion host traffic is load balanced across all four routers .

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FHRPs: VRRP

VRRP is the standardized FHRP that does exactly what HSRP does, however it works slightly different and can be used in a multi vendor environment.  Here are the differences between HSRP and VRRP:

  • VRRP uses a multicast virtual MAC 0000.5e00.01XX where XX is the hex value of the VRRP group number
  • VRRP uses IOS object tracking to track interface states
  • VRRP defaults with pre-emption, HSRP does not.  Both aare configurable
  • The VRRP Master means the same as HSRP Active
  • VRRP group IP is the interface address of one of the VRRP routers, it is not a virtual IP

 

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FHRPs: HSRP

HSRP allows multiple routers to share a virtual IP and MAC address so that hosts on a network don’t detect or realize a failure if one occurs on the primary gateway router.  Here are some features of HSRP:

  • The Virtual IP and Virtual MAC are active on the HSRP Active router
  • Standby routers listen for Hellos from the Active router, this is defaulted to 3 second hello interval with a 10 sec dead timeout
  • Higher priority configured on an HSRP router determines the Active router, preemption is disabled by default, the priority range is between 1-255, the default priority value is 100
  • HSRP supports tracking, and the tracked objects can be tied to a priority where if an interface that is being tracked fails it will decrease the priority on that router.
  • There can be multiple HSRP groups configured on an interface up to 255
  • The Virtual MAC address is always 0000.0c07.acXX, where XX is the hex conversion of the HSRP group
  • The Virtual IP configured must be in the same subnet as the router interface it’s applied to on the LAN
  • The Virtual IP must be unique from any other device in the subnet or interfaces configured on the two redundant routers
  • HSRP supports clear text and MD5 authentication

HSRP has one Active router at a time, non-Active routers are considered to be in an idle state.  To provide load balancing between the two redundant routers, Multiple HSRP or MHSRP can be configured with multiple HSRP groups for each subnet, and assigning priority for the various groups to prefer one router or the other to be Active and allows for this load balancing.  To further support this method of load balancing the DHCP configuration would define one router as the default gateway and the other half would reference the other router as the default gateway, and they both would failover to each other.

HSRP is Cisco proprietary.

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FHRPs: HSRP, VRRP, GLBP

In today’s modern network implementations DHCP is the preferred choice of assigning hosts an IP address and setting the gateway for which they send all traffic to.  What if the gateway they send  traffic to blows up, or fails in some way and no longer forwards traffic from the hosts on the network, to other outside subnets or even the internet?

Enter the First Hop Redundancy Protocols (FHRPs) Hot Standby Router Protocol, (HSRP), Virtual Router Redundancy Protocol (VRRP), and Gateway Load Balancing Protocol (GLBP) are the three flavors of FHRPs you can use to ensure redundant and transparent gateway connectivity for hosts on your network in the event  the primary gateway router goes down.

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