HSRP, VRRPd, and GLBP Compared
- Tony Mattke
- Routing
- October 21, 2010
- 5 min read
In the world of first hop redundancy, we have plenty of choices. In order to make the right decision for your network you should know the basics regarding all three. The following chart provides a quick breakdown of each protocol.
Hot Standby Router Protocol
When implementing HSRP, two or more routers are configured with the standby IP on a broadcast interface, usually an Ethernet segment, and a passive election is held to determine the active router. The active router answers ARP requests for the standby IP with a virtual MAC address, so every host that sends packets to the standby IP winds up sending it to the active router. If the active router dies, another election is held.
HSRP Configuration
Configuration Options
Router(config)#int fa 0/0
Router(config-if)#ip address 10.0.1.2 255.255.255.0
Router(config-if)#standby 1 ip 10.0.1.1
Router(config-if)#standby 1 preempt
Router(config-if)#standby version ?
<1-2> Version number
Router(config-if)#standby 1 timers ?
<1-254> Hello interval in seconds
msec Specify hello interval in milliseconds
Router(config-if)#standby 1 timers 10 ?
<11-255> Hold time in seconds
Router(config-if)#standby 1 priority ?
<0-255> Priority value
Router(config-if)#standby 1 authentication md5 key-string ?
0 Specifies an UNENCRYPTED key string will follow
7 Specifies a HIDDEN key string will follow
WORD Key string (64 chars max)Sample Config
interface FastEthernet0/0
ip address 10.0.1.2 255.255.255.0
standby version 2
standby 1 ip 10.0.1.1
standby 1 timers 3 10
standby 1 priority 110
standby 1 preempt
standby 1 authentication md5 key-string r0ut3roneVirtual Router Redundancy Protocol
VRRP is a non-proprietary (read: open standard) first hop redundancy protocol that was actually based off of Cisco’s HSRP. In a VRRP configuration, one router is elected as the virtual router master, with the other routers acting as backups in case the virtual router master fails. One benefit to using VRRP in addition to it being an open standards protocol, is that you can configure an interfaces original IP as the virtual IP address for the group.
VRRP Configuration
Configuration Options
Router(config)#int fa 0/0
Router(config-if)#ip address 10.0.1.2 255.255.255.0
Router(config-if)#vrrp 1 ip 10.0.1.1
Router(config-if)#vrrp 1 timers ?
advertise Set the Advertisement timer
learn Learn timer values from current Master
Router(config-if)#vrrp 1 timers advertise ?
<1-255> Advertisement interval in seconds
msec Specify time in milliseconds
Router(config-if)#vrrp 1 priority ?
<1-254> Priority level
Router(config-if)#vrrp 1 preempt
Router(config-if)#vrrp 1 auth md5 key-string ?
0 Specifies an UNENCRYPTED key string will follow
7 Specifies a HIDDEN key string will follow
WORD Key string (64 chars max)Sample Config
interface FastEthernet0/0
ip address 10.0.1.2 255.255.255.0
vrrp 1 ip 10.0.1.1
vrrp 1 timers 1 4
vrrp 1 priority 110
vrrp 1 preempt
vrrp 1 authentication md5 key-string r0ut3roneGateway Load Balancing Protocol
GLBP provides a standby IP just as HSRP, but it also provides multiple virtual MAC addresses. When a host on the connected network sends an ARP request, one of the routers answers with the virtual MAC address. The next time a host ARPs, a different router answers with a different virtual MAC address. This allows you to load balancing traffic across each router doing GLBP via the virtual MACs, although its impossible for this to pan out in the real world due to the way machines send ARP requests. If a router vanishes, one of the other participating routers takes over for that virtual MAC. GLBP is the only protocol of the three that provides native load balancing.
GLBP Configuration
Configuration Options
Router(config)#int fa 0/0
Router(config-if)#ip address 10.0.1.2 255.255.255.0
Router(config-if)#glbp 1 ip 10.0.1.1
Router(config-if)#glbp 1 timers ?
<1-60> Hello interval in seconds
msec Specify hello interval in milliseconds
redirect Specify timeout values for failed forwarders
Router(config-if)#glbp 1 timers 1 ?
<2-180> Hold time in seconds
msec Specify hold time in milliseconds
Router(config-if)#glbp 1 timers redirect ?
<0-3600> Interval in seconds to redirect to failed forwarders
Router(config-if)#glbp 1 timers redirect 10 ?
<610-64800> Timeout interval in seconds for failed forwarders
Router(config-if)#glbp 1 priority ?
<1-255> Priority value
Router(config-if)#glbp 1 preempt
Router(config-if)#glbp 1 forwarder preempt
Router(config-if)#glbp 1 auth md5 key-string ?
0 Specifies an UNENCRYPTED key string will follow
7 Specifies a HIDDEN key string will follow
WORD Key string (64 chars max)
Router(config-if)#glbp 1 load-balancing ?
host-dependent Load balance equally, source MAC determines forwarder choice
round-robin Load balance equally using each forwarder in turn
weighted Load balance in proportion to forwarder weighting
<cr>Sample Config
interface FastEthernet0/0
ip address 10.0.1.2 255.255.255.0
glbp 1 ip 10.0.1.1
glbp 1 timers 1 4
glbp 1 priority 110
glbp 1 preempt
glbp 1 authentication md5 key-string r0ut3roneConclusion
Do you actually expect me to tell you which one of these is best for your network? The answer is highly subjective and has to fit your needs. While I didn’t cover all the options ( a few that I left out that come to mind are Common Address Redundancy Protocol (CARP) and Routed Split Multi-Link Trunking (RSMLT) — both of which are not implement in IOS), I hope to of given you enough to go on to make an educated decision. As always, please direct any questions you may have to the comments and I’ll try to get back with you as soon as possible.
