© 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-1

Implementing Layer 3 High Availability

Configuring Layer 3 Redundancy with VRRP and GLBP

© 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-2

HSRP vs. VRRP

HSRP VRRPCisco proprietary, 1994. IETF 1998–2005, RFC 3768.

16 groups max. 255 groups max.

1 active, 1 standby, several candidates.

1 active, several backups.

Virtual IP is different from active and standby real IP addresses.

Virtual IP address can be the same as the real IP address of one of the group members.

Uses 224.0.0.2. Uses 224.0.0.18.

Can track interfaces or objects. Can track only objects.

Default timers: hello, 3 sec; hold time, 10 sec.

Default timers: hello, 1 sec; hold time, 3 sec.

Authentication supported. Authentication no longer supported.

© 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-3

About VRRP

© 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-4

VRRP Operations Process

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VRRP Configuration

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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—6-7

GLBP vs. HSRP

HSRP GLBP

Cisco proprietary, 1994. Cisco proprietary, 2005.

16 groups max. 1024 groups max.

1 active, 1 standby, several candidates.

1 AVG, several AVFs; AVG load-balances traffic among AVFs and AVG.

Virtual IP is different from active and standby real IP addresses.

Virtual IP is different from AVG and AVF real IP addresses.

1 virtual MAC address for each group.

1 virtual MAC address per AVF or AVG in each group.

Uses 224.0.0.2. Uses 224.0.0.102.

Can track interfaces or objects. Can track only objects.

Default timers: hello, 3 sec; hold time, 10 sec.

Default timers: hello, 3 sec; hold time, 10 sec.

Authentication supported. Authentication supported.

© 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-8

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—6-9

GLBP Operation

© 2009 Cisco Systems, Inc. All rights reserved. SWITCH v1.0—6-10

GLBP Operation (Cont.)

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GLBP Interface Tracking

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GLBP Interface Tracking (Cont.)

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GLBP Weights and Decrements

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GLBP Configuration

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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—6-16

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—6-17