%STANDBY-6-STATECHANGE: Vlan11 Group 11 state
Listen -> Active
*Mar 1 00:16:43.299: SB11: Vl11 Hello
out 172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1
00:16:43.303: SB11: Vl11 Hello in 172.16.11.112 Speak pri 50 ip
172.16.11.115
*Mar 1 00:16:44.095: %LINEPROTO-5-UPDOWN:
Line protocol on Interface Vlan11, changed state to up
*Mar
1 00:16:46.187: SB11: Vl11 Hello in 172.16.11.112 Speak pri 50
ip 172.16.11.115
*Mar 1 00:16:46.207: SB11: Vl11 Hello out
172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1
00:16:49.095: SB11: Vl11 Hello in 172.16.11.112 Speak pri 50 ip
172.16.11.115
*Mar 1 00:16:49.195: SB11: Vl11 Hello out
172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1
00:16:52.079: SB11: Vl11 Hello in 172.16.11.112 Speak pri 50 ip
172.16.11.115
*Mar 1 00:16:52.147: SB11: Vl11 Hello out
172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1
00:16:53.303: SB11: Vl11 Hello in 172.16.11.112 Standby pri 50
ip 172.16.11.115
*Mar 1 00:16:53.303: SB11: Vl11 Standby
router is 172.16.11.112
*Mar 1 00:16:55.083: SB11: Vl11
Hello out 172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1 00:16:56.231: SB11: Vl11 Hello in 172.16.11.112 Standby
pri 50 ip 172.16.11.115
*Mar 1 00:16:58.023: SB11: Vl11
Hello out 172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1 00:16:59.223: SB11: Vl11 Hello in 172.16.11.112 Standby
pri 50 ip 172.16.11.115
*Mar 1 00:17:00.983: SB11: Vl11
Hello out 172.16.11.111 Active pri 100 ip 172.16.11.115
*Mar 1 00:17:02.211: SB11: Vl11 Hello in 172.16.11.112 Standby
pri 50 ip 172.16.11.115
*Mar 1 00:17:03.847: SB11: Vl11
Hello out 172.16.11.111 Active pri 100 ip 172.16.11.115
Content 5.3 Configuring Layer 3
Redundancy with VRRP and GLBP 5.3.1 Describing
Virtual Router Redundancy Like HSRP, Virtual Router
Redundancy Protocol (VRRP) allows a group of routers to form a
single virtual router. In an HSRP or VRRP group, one router is
elected to handle all requests sent to the virtual IP address.
With HSRP, this is the active router. An HSRP group has one
active router, at least one standby router, and perhaps many
listening routers. A VRRP group has one master router and one
or more backup routers. The LAN workstations are then
configured with the address of the virtual router as their
default gateway. VRRP differs from HSRP in the following ways:
- VRRP is an IEEE standard (RFC 2338) for router
redundancy; HSRP is a Cisco-proprietary protocol.
- The
virtual router represents a group of routers, known as a VRRP
group or virtual router group.
- The active router is
referred to as the master virtual router.
- The master
virtual router may have the same IP address as the virtual
router group.
- Multiple routers can function as backup
routers.
- VRRP is supported on Ethernet, Fast
Ethernet, and Gigabit Ethernet interfaces, and with
Multiprotocol Label Switching (MPLS), virtual private networks
(VPNs), and VLANs.
In Figure , routers A, B, and C
are members of a VRRP group. The IP address of the virtual
router is the same as that of the LAN interface of router A
(10.0.0.1). Router A is responsible for forwarding packets sent
to this IP address. The clients have a gateway address of
10.0.0.1. Routers B and C are backup routers. If the master
router fails, the backup router with the highest priority
becomes the master router. When router A recovers, it resumes
the role of master router. VRRP provides redundancy for the
real IP address of a router or for a virtual IP address shared
among the VRRP group members. If a real IP address is used, the
router with that address becomes the master. If a virtual IP
address is used, the master is the router with the highest
priority. The master router uses VRRP messages to inform group
members that it is the master.
Content
5.3 Configuring Layer 3 Redundancy
with VRRP and GLBP 5.3.2 Identifying the VRRP
Operations Process Figure shows a LAN topology in which
VRRP is configured so that routers A and B share the load of
being the default gateway for clients 1 through 4. Routers A
and B act as backup virtual routers to one another should
either one fail. In this example, two virtual router groups are
configured. For virtual router 1, router A is the owner of IP
address 10.0.0.1, and therefore the master virtual router for
clients configured with that default gateway address. Router B
is the backup virtual router to router A. For virtual router 2,
router B is the owner of IP address 10.0.0.2 and is the master
virtual router for clients configured with the default gateway
IP address of 10.0.0.2. Router A is the backup virtual router
to router B. Given that the IP address of the VRRP group is
that of a physical interface on one of the group members, the
router owning that address is the master in the group. Its
priority is set to 255. Backup router priority values can range
from 1 to 254; the default is 100. A priority value of 0
indicates that the current master has stopped participating in
VRRP. This setting is used to trigger backup routers to
transition quickly to the master without having to wait for the
current master to time out. With VRRP, only the master sends
advertisements (the equivalent of HSRP hellos). Advertisements
are sent on multicast 224.0.0.18 protocol number 112 at a
default interval of 1 second. When the master becomes
unavailable, the dynamic failover uses three timers: the
advertisement interval, the master down interval, and the skew
time. - The advertisement interval is the time between
advertisements in seconds. The default is 1 second.
-
The master down interval is the number of seconds for the
backup to declare the master down. The default is 3 x
advertisement interval + skew time.
- The skew time,
(256 - priority) / 256 ms, ensures that the backup router with
the highest priority becomes the new master.
Figure
lists the steps involved in the VRRP transition. Note:
If the VRRP master has an orderly shutdown, it sends an
advertisement with a priority of 0. This priority setting then
triggers the backup router to take over quicker by waiting only
the skew time instead of the master down interval.
Content 5.3 Configuring Layer 3
Redundancy with VRRP and GLBP 5.3.3 Configuring
VRRP VRRP is supported on select Cisco Catalyst platforms
and can be configured using the commands in Figure . Figure
describes the VRRP command parameters. Figure describes how to
configure VRRP. Example: Implementing VRRP
SwitchA(config)#interface vlan10
SwitchA(config-if)#ip address 10.1.10.5
255.255.255.0
SwitchA(config-if)#vrrp 10 ip
10.1.10.1
SwitchA(config-if)#vrrp 10 priority
150
SwitchA(config-if)#vrrp 10 timer advertise
4 SwitchB(config)#interface vlan10
SwitchB(config-if)#ip address 10.1.10.6
255.255.255.0
SwitchB(config-if)#vrrp 10 ip
10.1.10.1
SwitchB(config-if)#vrrp 10 priority
100
SwitchB(config-if)#vrrp 10 timer advertise
4
Content 5.3 Configuring Layer 3
Redundancy with VRRP and GLBP 5.3.4 Describing
GLBP While HSRP and VRRP provide gateway resiliency, the
upstream bandwidth is not used for the standby members of the
redundancy group while the device is in standby mode. Only the
active router for HSRP and VRRP groups forwards traffic for the
virtual MAC. Resources associated with the standby router are
not fully utilized. Some load balancing can occur by creating
multiple groups and assigning multiple default gateways, but
this configuration creates an administrative burden. Cisco
designed the Gateway Load Balancing Protocol (GLBP) to allow
automatic selection, simultaneous use of multiple gateways, and
automatic failover between those gateways. Multiple routers
share the load of frames that, from a client perspective, are
sent to a single default gateway address. With GLBP, resources
can be fully utilized without the administrative burden of