Layer 3 Redundancy

Question 1

FHRP

Answer 1

first hop redundancy protocol. a general category of protocols containing GLBP, HSRP, and VRRP

Question 2

HSRP

Answer 2

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.

Question 3

VRRP

Answer 3

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.

Question 4

GLBP

Answer 4

Gateway Load Balancing Protocol

an FHRP that is designed by Cisco to allow multiple active forwarders to load-balance outgoing traffic.

Question 5

responsibilities of HSRP primary router

Answer 5

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

Question 6

responsiblities of HSRP backup router

Answer 6

Listens for periodic hello messages from the active router

Assumes the role of default gateway if it does not hear from the active router

Question 7

default HSRP interface priority

Answer 7

100

Question 8

HSRP interface tracking

Answer 8

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.

Question 9

what is preemption in the context of HSRP

Answer 9

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.

Question 10

command to enable HSRP interface tracking on an interface

Answer 10

(config-if)standby [group #] track [interface #] [decrement level, ie 15]

Question 11

command to enable preemption in HSRP

Answer 11

(config-if)standby [group #] preempt

Question 12

command to enable HSRP group

Answer 12

standby [group #] ip [virtual ip address]

Question 13

command to name HSRP group

Answer 13

standby name [group name]

Question 14

HSRP load balancing

Answer 14

can load balance across trunk links sending one vlan over active router and one vlan over passive router

Question 15

command to enable VRRP

Answer 15

the same as HSRP, just replace “standby” with “vrrp”

ie vrrp [group #] ip [virtual ip address]

Question 16

command to name VRRP group

Answer 16

vrrp description [name]

Question 17

command to configure a VRRP tracking

Answer 17

track [object #] interface [int face #] {line-protocol | IP routing}

Question 18

command to enable a VRRP interface to be tracked

Answer 18

vrrp [group] track [object number] [decrement priority]

Question 19

What are the advantages of GLBP over HSRP and VRRP?

Answer 19

fast failover
low overhead
simple configuration
load balancing

Question 20

What is the active router called in GLBP?

Answer 20

active virtual gateway, or AVG

Question 21

What are the failover routers called GLBP?

Answer 21

active virtual forwarder, or AVF

* there can be up to 4 of these

Question 22

GLBP group

Answer 22

Configures up to four routers with the same GLBP group number

Question 23

GLBP gateway

Answer 23

Router that runs GLBP, which may participate in one or more GLBP groups

Question 24

AVG in GLBP

Answer 24

Elected router that is responsible for operation of the protocol (allocating MAC addresses)

Question 25

SVG IN GLBP

Answer 25

Elected router that is the next AVG candidate

Question 26

AVF in GLBP

Answer 26

Router in a GLBP group that forwards packets for a particular virtual MAC address; multiple AVFs may exist in a GLBP group

Question 27

SVF in GLBP

Answer 27

Router that has learned the virtual MAC address of other AVFs

Question 28

GLBP command examples

Answer 28

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

Question 29

commands to configure interface tracking for GLBP

Answer 29

Use the track interface and glbp weighting track commands to configure object tracking for an interface.

Question 30

glbp [group-number] ip [ip-address]

Answer 30

Establishes the VRRP VRID and the virtual router IP address

Question 31

glbp [group-number] load-balancing [host-dependent | round-robin | weighted]

Answer 31

Selects the GLBP load-balancing mode

Question 32

glbp [group-number] name [group-name]

Answer 32

Assigns a user-defined label to the GLBP group

Question 33

track object-number interface type number {line-protocol | ip routing}

Answer 33

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.

Question 34

glbp [group] weighting track object-number [decrement value]

Answer 34

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.

Question 35

GLBP round robin load balancing

Answer 35

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.

Question 36

GLBP weighted load balancing

Answer 36

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.

Question 37

GLBP host-dependent load balancing

Answer 37

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.