Layer 3 Redundancy Flashcards
FHRP
first hop redundancy protocol. a general category of protocols containing GLBP, HSRP, and VRRP
HSRP
Hot Standy Router Protocol
Designed by Cisco. Provides high network availability and transparent network topology changes. HSRP creates a hot standby router group with a lead router that services all packets sent to the hot standby address. The lead router is monitored by other routers in the group. If it fails, one of the standby routers inherits both the lead position and the hot standby address.
VRRP
Virtual Router Redundancy Protocl
an open FHRP standard that is characterized by the ability to add more than two routers for additional redundancy. Only one router forwards traffic. VRRP is defined in RFC 5798.
GLBP
Gateway Load Balancing Protocol
an FHRP that is designed by Cisco to allow multiple active forwarders to load-balance outgoing traffic.
responsibilities of HSRP primary router
Responds to ARP requests for the default gateway with the MAC address of the virtual router
Assumes the role of active default gateway for the virtual router
Sends periodic hello messages
Knows the virtual router IP address
responsiblities of HSRP backup router
Listens for periodic hello messages from the active router
Assumes the role of default gateway if it does not hear from the active router
default HSRP interface priority
100
HSRP interface tracking
If a tracked interface (member of hsrp) goes down a hello packet is sent out with a decremented priority for the interface. Must be explicitly configured on each participating interface.
what is preemption in the context of HSRP
Preemption allows one HSRP peer to proactively elevate itself to the Active router role if its peer has a lower HSRP priority. Must be explicitly configured on each participating interface.
command to enable HSRP interface tracking on an interface
(config-if)standby [group #] track [interface #] [decrement level, ie 15]
command to enable preemption in HSRP
(config-if)standby [group #] preempt
command to enable HSRP group
standby [group #] ip [virtual ip address]
command to name HSRP group
standby name [group name]
HSRP load balancing
can load balance across trunk links sending one vlan over active router and one vlan over passive router
command to enable VRRP
the same as HSRP, just replace “standby” with “vrrp”
ie vrrp [group #] ip [virtual ip address]
command to name VRRP group
vrrp description [name]
command to configure a VRRP tracking
track [object #] interface [int face #] {line-protocol | IP routing}
command to enable a VRRP interface to be tracked
vrrp [group] track [object number] [decrement priority]
What are the advantages of GLBP over HSRP and VRRP?
fast failover
low overhead
simple configuration
load balancing
What is the active router called in GLBP?
active virtual gateway, or AVG
What are the failover routers called GLBP?
active virtual forwarder, or AVF
* there can be up to 4 of these
GLBP group
Configures up to four routers with the same GLBP group number
GLBP gateway
Router that runs GLBP, which may participate in one or more GLBP groups
AVG in GLBP
Elected router that is responsible for operation of the protocol (allocating MAC addresses)
SVG IN GLBP
Elected router that is the next AVG candidate
AVF in GLBP
Router in a GLBP group that forwards packets for a particular virtual MAC address; multiple AVFs may exist in a GLBP group
SVF in GLBP
Router that has learned the virtual MAC address of other AVFs
GLBP command examples
R2#config t R2(config)#interface e0/0 R2(config-if)#ip address 10.10.1.3 255.255.255.0 R2(config-if)#glbp 1 ip 10.10.1.1 R2(config-if)#glbp 1 load-balancing host-dependent R2(config-if)#glbp 1 name GLBP-1 R2(config-if)#end R2#
show glbp
commands to configure interface tracking for GLBP
Use the track interface and glbp weighting track commands to configure object tracking for an interface.
glbp [group-number] ip [ip-address]
Establishes the VRRP VRID and the virtual router IP address
glbp [group-number] load-balancing [host-dependent | round-robin | weighted]
Selects the GLBP load-balancing mode
glbp [group-number] name [group-name]
Assigns a user-defined label to the GLBP group
track object-number interface type number {line-protocol | ip routing}
To configure an interface to be tracked and to enter tracking configuration mode, use the track interface command in global configuration mode. To remove the tracking, use the no form of this command.
glbp [group] weighting track object-number [decrement value]
To specify a tracking object where the GLBP weighting changes based on the availability of the object being tracked, use the glbp weighting track command in interface configuration mode. To remove the tracking, use the no form of this command.
GLBP round robin load balancing
Each virtual forwarder MAC address takes turns being included in address resolution replies for the virtual lP address. Round-robin load balancing is recommended for situations where there are a small number of end hosts.
GLBP weighted load balancing
The amount of load that is directed to an AVF depends on the weighting value that is advertised by the gateway that contains that AVF.
GLBP host-dependent load balancing
The MAC address of a host is used to determine which virtual forwarder MAC address that host is directed toward. This ensures that a host will be guaranteed to use the same virtual MAC address as long as that virtual MAC address is participating in the GLBP group.
Host-dependent load balancing is required for IP redundancy. IP redundancy is used for stateful failover, and this requires that each host receive the same virtual MAC address each time it uses ARP to get the virtual IP address.
