Configuring Layer 3
Redundancy with
VRRP and GLBP
Implementing Layer 3 High Availability
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-1
HSRP vs. VRRP
HSRP
VRRP
Cisco proprietary, 1994.
IETF 1998–2005, RFC 3768.
16 groups max.
255 groups max.
1 active, 1 standby, several
candidates.
Virtual IP is different from active and
standby real IP addresses.
1 active, several backups.
Uses 224.0.0.2.
Virtual IP address can be the same
as the real IP address of one of the
group members.
Uses 224.0.0.18.
Can track interfaces or objects.
Can track only objects.
Default timers: hello, 3 sec; hold
time, 10 sec.
Authentication supported.
Default timers: hello, 1 sec; hold
time, 3 sec.
Authentication no longer supported.
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-2
About VRRP
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-3
VRRP Operations Process
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-4
VRRP Configuration
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-5
About GLBP
 Allows full use of resources on all devices without the
administrative burden of creating multiple groups
 Provides a single virtual IP address and multiple virtual MAC
addresses
 Routes traffic to single gateway distributed across routers
 Provides automatic rerouting in the event of any failure
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-6
GLBP vs. HSRP
HSRP
Cisco proprietary, 1994.
16 groups max.
1 active, 1 standby, several
candidates.
Virtual IP is different from active and
standby real IP addresses.
1 virtual MAC address for each
group.
Uses 224.0.0.2.
Can track interfaces or objects.
Default timers: hello, 3 sec; hold
time, 10 sec.
Authentication supported.
© 2009 Cisco Systems, Inc. All rights reserved.
GLBP
Cisco proprietary, 2005.
1024 groups max.
1 AVG, several AVFs; AVG loadbalances traffic among AVFs and
AVG.
Virtual IP is different from AVG and
AVF real IP addresses.
1 virtual MAC address per AVF or
AVG in each group.
Uses 224.0.0.102.
Can track only objects.
Default timers: hello, 3 sec; hold
time, 10 sec.
Authentication supported.
SWITCH v1.0—6-7
GLBP Operations
 GLBP group members elect one AVG.
 AVG assigns a virtual MAC address to each member of the group.
 AVG replies to the ARP requests from clients with different virtual
MAC addresses, thus achieving load balancing.
 Each router becomes an AVF for frames that are addressed to
that virtual MAC address.
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-8
GLBP Operation
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-9
GLBP Operation (Cont.)
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-10
GLBP Interface Tracking
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-11
GLBP Interface Tracking (Cont.)
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-12
GLBP Weights and Decrements
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-13
GLBP Configuration
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-14
GLBP and VLAN Spanning
 Both distribution switches act as a default gateway.
 Blocked uplink causes traffic to take a less-than-optimal path.
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-15
Summary
 VRRP provides router redundancy in a manner similar to that of
HSRP.
 VRRP supports a master router and one or more backup routers.
 VRRP is configured per interface.
 GLBP provides router redundancy and load balancing.
 GLBP balances traffic by allocating a virtual MAC address to each
AVF.
 The GLBP configuration steps are very similar to those of HSRP
and VRRP.
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-16
© 2009 Cisco Systems, Inc. All rights reserved.
SWITCH v1.0—6-17