First Hop Redudancy Protocols Flashcards
FHRP Availble
Hot Standby Router Protocl (HSRP):
Cisco proprietary
Active and Standby routers
Virtual Router Redudancy Protocol (VRRP):
IEEE variation, behaves like HSRP
Gateway Load Balancing Protocol (GLBP):
Cisco Proprietary
Uses Active Virtual Forwarding (AVF) routers
Multiple AVFs can exist in a GLBP group
HSRP
Has one active and one standby router
Both routers know the virtual IP address and use a virtual MAC address, which is used in ARP requests.
Only the active router will respond to the ARP request.
HSRP with STP
STP root switch and HSRP active router should be configured on the same switch, otherwise traffic flow is not optimal.
HSRP and vPC
Whenever a vPC peer switch needs to forward traffic for a vPC, it will forward it to a local vPC port if possible.
Normally, only the active HSRP router forwards traffic that is received for the virtual default gateway MAC address
For vPCs, Cisco enhanced the forwarding rules to allow the standby router to forward frames destined for the virtual MAC address.
The result is that the vPC peer linnk between the active and standby routers does not carry vPC traffic unless there is a failure.
HSRP Election
Router with highest priority will be assigned as active
If both have same priority, router with the highest active IP address will be assigned active
HSRP Configuration
feature hsrp
interface x
ip address x.x.x.x x.x.x.x
hsrp 40
priority 100
preempt (router with highest priority will always be active i.e. will take over from
an active router with lower priority)
preempt delay minimum 60 (delays active takeover for specified number of
seconds, to ensure all services ready etc)
ip [virtual ip address]
HSRP Interface Tracking
Allows monitoring of uplink ports to prevent active router having no uplinks to use for forwarding traffic.
HSRP Interface Tracking Configuration
track 1 interface eth 1/1 line-protocol
track 2 interface eth 1/2 line-protocol
!
interface vlan 40
ip-address 10.40.40.2
hsrp 40
priority 100
track 1 decrement 15 (if track 1 interface goes down, priority decreases by
specified decrement amount)
track 2 decrement 15VRRP
Virtual Router Redundancy Protocol
Used in multi-vendor environment, standardized in IEEE.
Fowarding router is the master and the standby are backup.
The virtual VRRP address can be one of the physical IP addresses of the VRRP group members.
VRRP Master
Device with its physical address assigned as the group virtual address will be the master router whenever it is available.
The master is the only device that sends advertisements every second to 244.0.0.18 with protocol number 112.
Default hold time is 3 seconds. Compared to HSRP which sends hellos every 3 seconds and has a hold time of 10 seconds.
Use milliisecond timers only when necessary and with careful consideration, testing and only under favorable circumstances.
FHRP on IPv6
Uses ICMP 134 packers, known as router advertisements to advertise themselves as a default gateway.
In the event a router goes down however it can take 40 seconds to move to using another.
FHRP on IPv6 Considerations
Native IPv6 redundancy is slow, not viable for modern datacentres.
Failover is not possible, have to wait for route to timeout.
Can use technology like DHCPv6 instead, which can provide endpoints with multiple gateways.
FHRP offers more features and control such as preemption (one router will be active whenever it is available), timers (subsecond failovers) and tracking (give up active role in the event uplink goes down).
HSRP and VRRP have support for IPv6, but not in all releases. VRRP for IPv6 is less frequently supported, but it is supported on all recent Nexus releases.
Gateway Load Balancing Protocol (GLBP)
All routers in the group participate in forwarding
More resilient and efficient than HSRP but not supported on all nexus releases.
One router will become the active virtual gateway (AVG), which responds to ARP requests with its virtual MAC address, and the virtual MAC address of other active virtual forwarders (AVF) in a round robin fashion to distribute traffic load.
