IP Services: HSRP, VRRP, GLBP

HSRP:

  • sends it’s multicast hello messages to 224.0.0.2 (all routers) UDP port 1985
  • Primary router with the highest configured priority will act as a virtual router with its own IP and MAC address.
  • single router, elected from the group is responsible for forwarding the packets that hosts send to the virtual router. The router is known as the Active router. Another router is elected as the standby router.
  • only the active and standby routers send periodic HSRP messages once the protocol has completed election.
  • HSRP default is 100.
  • Hello Messages: 3 seconds, dead interval: 10 seconds.
  • Coup: when standby router takes over, it sends a coup message
  • Resign: when active router is shut down or when a router with higher priority sends its hello message. Active router sends “Resign”
  • Upto 255 HSRP groups per interface
  • MAC of 0000.0C07.ACxx, where xx is hex HSRP group.
  • Virtual IP address MUST be different from any routers’ individual interface IP address.
  • Tracking interface: A tracking object can track based on the line protocol or the IP routing table. “track 13 interface s0/0.1 line-protocol
  • Configuring HSRP: (int) standby 21 ip 10.1.1.21 à standby 21 preempt à standby 21 track 13
  • default decrement is 10, meaning that configured priority will be decremented by 10 if the interface fails.
  • MHSRP: load sharing in an HSRP configuration. Each host is issued a default gateway corresponding to one of the HSRP groups and requires they’re distributed properly.

VRRP:

  • based on standard, has exact same features as HSRP.
  • Multicast MAC of 0000.5E00.01xx (x is the hex VRRP group number)
  • uses IOS object tracking feature rather that its own internal tracking mechanism. HSRP can use both, it’s internal or IOS object tracking feature.
  • VRRP default to pre-emption, HSRP does not default to pre-emption.
  • Master == Active
  • VRRP IP address is the interface IP address of one of the VRRP routers.

GLBP:

  • Cisco proprietary
  • adds load-balancing in addition to gateway redundancy
  • Causes different hosts to send their traffic to one of up to four routers in a GLBP group.
  • Active Virtual Gateway (AVG) assigns each router in the group a unique virtual MAC address, following the format: 0007.B400.xxyy (where xx is the GLBP group number and yy is the different number of each router, 01, 02…)
  • when client ARPs, for the virtual IP, it can get different virtual MAC, the host can effectively balance traffic.
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