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The Virtual Router Redundancy Protocol (VRRP) feature allows for transparent failover at the first-hop IP router, enabling a group of routers to form a single virtual router.
|
Release |
Modification |
|---|---|
| Release 5.0.0 |
This feature was introduced. |
You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
To implement VRRP on Cisco IOS XR software , you need to understand the following concepts:
A LAN client can use a dynamic process or static configuration to determine which router should be the first hop to a particular remote destination. The client examples of dynamic router discovery are as follows:
Proxy ARP—The client uses Address Resolution Protocol (ARP) to get the destination it wants to reach, and a router responds to the ARP request with its own MAC address.
Routing protocol—The client listens to dynamic routing protocol updates (for example, from Routing Information Protocol [RIP]) and forms its own routing table.
IRDP (ICMP Router Discovery Protocol) client—The client runs an Internet Control Message Protocol (ICMP) router discovery client.
The drawback to dynamic discovery protocols is that they incur some configuration and processing overhead on the LAN client. Also, in the event of a router failure, the process of switching to another router can be slow.
An alternative to dynamic discovery protocols is to statically configure a default router on the client. This approach simplifies client configuration and processing, but creates a single point of failure. If the default gateway fails, the LAN client is limited to communicating only on the local IP network segment and is cut off from the rest of the network.
The Virtual Router Redundancy Protocol (VRRP) feature can solve the static configuration problem. VRRP is an IP routing redundancy protocol designed to allow for transparent failover at the first-hop IP router. VRRP enables a group of routers to form a single virtual router . The LAN clients can then be configured with the virtual router as their default gateway. The virtual router, representing a group of routers, is also known as a VRRP group.
For example, Figure 1 shows a LAN topology in which VRRP is configured. In this example, Routers A, B, and C are VRRP routers (routers running VRRP) that compose a virtual router. The IP address of the virtual router is the same as that configured for the interface of Router A (10.0.0.1).
Because the virtual router uses the IP address of the physical interface of Router A, Router A assumes the role of the master virtual router and is also known as the IP address owner. As the master virtual router, Router A controls the IP address of the virtual router and is responsible for forwarding packets sent to this IP address. Clients 1 through 3 are configured with the default gateway IP address of 10.0.0.1.
Routers B and C function as backup virtual routers. If the master virtual router fails, the router configured with the higher priority becomes the master virtual router and provides uninterrupted service for the LAN hosts. When Router A recovers, it becomes the master virtual router again.
 Note |
We recommend that you disable Spanning Tree Protocol (STP) on switch ports to which the virtual routers are connected. Enable RSTP or rapid-PVST on the switch interfaces if the switch supports these protocols. |
You can configure up to 255 virtual routers on a router physical interface. The actual number of virtual routers that a router interface can support depends on the following factors:
Router processing capability
Router memory capability
Router interface support of multiple MAC addresses
In a topology where multiple virtual routers are configured on a router interface, the interface can act as a master for one or more virtual routers and as a backup for one or more virtual routers.
An important aspect of the VRRP redundancy scheme is VRRP router priority. Priority determines the role that each VRRP router plays and what happens if the master virtual router fails.
If a VRRP router owns the IP address of the virtual router and the IP address of the physical interface, this router functions as a master virtual router.
Priority also determines if a VRRP router functions as a backup virtual router and determines the order of ascendancy to becoming a master virtual router if the master virtual router fails. You can configure the priority of each backup virtual router with a value of 1 through 254, using the vrrp priority command.
For example, if Router A, the master virtual router in a LAN topology, fails, an election process takes place to determine if backup virtual Routers B or C should take over. If Routers B and C are configured with the priorities of 101 and 100, respectively, Router B is elected to become master virtual router because it has the higher priority. If Routers B and C are both configured with the priority of 100, the backup virtual router with the higher IP address is elected to become the master virtual router.
By default, a preemptive scheme is enabled whereby a higher-priority backup virtual router that becomes available takes over for the backup virtual router that was elected to become master virtual router. You can disable this preemptive scheme using the no vrrp preempt command. If preemption is disabled, the backup virtual router that is elected to become master virtual router remains the master until the original master virtual router recovers and becomes master again.
The master virtual router sends VRRP advertisements to other VRRP routers in the same group. The advertisements communicate the priority and state of the master virtual router. The VRRP advertisements are encapsulated in IP packets and sent to the IP Version 4 multicast address assigned to the VRRP group. The advertisements are sent every second by default; the interval is configurable.
The benefits of VRRP are as follows:
Redundancy— VRRP enables you to configure multiple routers as the default gateway router, which reduces the possibility of a single point of failure in a network.
Load Sharing—You can configure VRRP in such a way that traffic to and from LAN clients can be shared by multiple routers, thereby sharing the traffic load more equitably among available routers.
Multiple Virtual Routers—VRRP supports up to virtual routers (VRRP groups) on a router interface, subject to the platform supporting multiple MAC addresses. Multiple virtual router support enables you to implement redundancy and load sharing in your LAN topology.
Multiple IP Addresses—The virtual router can manage multiple IP addresses, including secondary IP addresses. Therefore, if you have multiple subnets configured on an Ethernet interface, you can configure VRRP on each subnet.
Preemption—The redundancy scheme of VRRP enables you to preempt a backup virtual router that has taken over for a failing master virtual router with a higher-priority backup virtual router that has become available.
Text Authentication—You can ensure that VRRP messages received from VRRP routers that comprise a virtual router are authenticated by configuring a simple text password.
Advertisement Protocol—VRRP uses a dedicated Internet Assigned Numbers Authority (IANA) standard multicast address (224.0.0.18) for VRRP advertisements. This addressing scheme minimizes the number of routers that must service the multicasts and allows test equipment to accurately identify VRRP packets on a segment. The IANA assigns VRRP the IP protocol number 112.
This section contains instructions for configuring VRRP for IPv4 and IPv6 networks.
Note |
The VRRP virtual router id (vrid) has to be different for different sub-interfaces, for a given physical interface. |
This section describes the procedure for configuring and verifying VRRP for IPv4 networks.
Use the following configuration for configuring VRRP for IPv4 networks.
Note |
Certain customizations (as mentioned) are recommended to control the behavior of the VRRP group on committing the VRRP configuration on the Router. If the following customizations are not configured, then the Router seizes control of the VRRP group, and immediately assumes the role of the master virtual Router. |
/* Enter the interface configuration mode and configure an IPv4 address for the interface. */
Router(config)# interface gigabitEthernet 0/0/0/1
Router(config-if)# ipv4 address 10.10.10.1 255.255.255.0
Router(config-if)# no shut
Router(config-if)# commit
Fri Dec 8 13:49:24.142 IST
Router:Dec 8 13:49:24.285 : ifmgr[402]: %PKT_INFRA-LINK-3-UPDOWN : Interface GigabitEthernet0/0/0/1, changed state to Down
Router:Dec 8 13:49:24.711 : ifmgr[402]: %PKT_INFRA-LINK-3-UPDOWN : Interface GigabitEthernet0/0/0/1, changed state to Up
Router(config-if)# exit
Router(config)# do show ip int brief
Fri Dec 8 13:50:05.505 IST
Interface IP-Address Status Protocol Vrf-Name
GigabitEthernet0/0/0/0 unassigned Shutdown Down default
GigabitEthernet0/0/0/1 10.10.10.1 Up Up default
GigabitEthernet0/0/0/2 unassigned Shutdown Down default
GigabitEthernet0/0/0/3 unassigned Shutdown Down default
GigabitEthernet0/0/0/4 unassigned Shutdown Down default
/* Enter the VRRP configuration mode and add the configured interface. */
Router(config)# router vrrp
Router(config-vrrp)# interface GigabitEthernet 0/0/0/1
/* CUSTOMIZATION: Configure a delay for the startup of the state machine when the interface comes up. */
Router(config-vrrp)# delay minimum 2 reload 10 */
/* Configure VRRP version 3 for IPv4 */
Router(config-vrrp-if)# address-family ipv4 vrrp 100 version 3
Router(config-vrrp-virtual-router)# address 10.10.10.1
/* CUSTOMIZATION: Disable the installation of routes for the VRRP virtual addresses. */
Router(config-vrrp-virtual-Router)# accept-mode disable
/* CUSTOMIZATION: Set a priority for the virtual Router. */
Router(config-vrrp-virtual-Router)# priority 254
/* CUSTOMIZATION: Configure a preempt delay value that controls the selection of the master virtual Router. */
Router(config-vrrp-virtual-Router)# preempt delay 15
/* CUSTOMIZATION: Configure the interval between successive advertisements by the master virtual Router. */
Router(config-vrrp-virtual-Router)#timer 4
/* CUSTOMIZATION: Configure VRRP to track an interface. */
Router(config-vrrp-virtual-Router)# track interface GigabitEthernet0/0/0/1 30
/* Commit the configuration */
Router(config-vrrp-virtual-Router)# commit
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––-You have successfully configured VRRP for IPv4 networks.
Use the following commands to validate the configuration.
/* Validate the configuration */
Router(config-vrrp-virtual-router)# do show run interface GigabitEthernet 0/0/0/1
Fri Dec 8 15:04:38.140 IST
interface GigabitEthernet0/0/0/1
ipv4 address 10.10.10.1 255.255.255.0
!
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––--
Router(config)# show running-config router vrrp
Fri Dec 8 13:50:18.959 IST
router vrrp
interface GigabitEthernet0/0/0/1
delay minimum 2 reload 10
address-family ipv4
vrrp 100 version 3
priority 254
preempt delay 15
timer 4
track interface GigabitEthernet0/0/0/2 30
address 10.10.10.1
accept-mode disable
!
!
!
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––--
Router(config-vrrp-virtual-router)# do show vrrp ipv4 interface gigabitEthernet 0/0/0/1
Fri Dec 8 15:02:56.952 IST
IPv4 Virtual Routers:
A indicates IP address owner
| P indicates configured to preempt
| |
Interface vrID Prio A P State Master addr VRouter addr
Gi0/0/0/1 100 255 A P Master local 10.10.10.1
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––--
Router(config-vrrp-virtual-router)# end
Router# show vrrp detail
Fri Dec 8 15:08:36.469 IST
GigabitEthernet0/0/0/1 - IPv4 vrID 100
State is Master, IP address owner
1 state changes, last state change 01:19:06
State change history:
Dec 8 13:49:30.147 IST Init -> Master Delay timer expired
Last resign sent: Never
Last resign received: Never
Virtual IP address is 10.10.10.1
Virtual MAC address is 0000.5E00.0164, state is active
Master router is local
Version is 3
Advertise time 1 secs
Master Down Timer 3.003 (3 x 1 + (1 x 1/256))
Minimum delay 1 sec, reload delay 5 sec
Current priority 255
Configured priority 100, may preempt
minimum delay 0 secs
You have successfully validated VRRP for IPv4 networks.
This section describes the procedure for configuring and verifying VRRP for IPv6 networks.
The following sample includes the configuration and customization of VRRP for IPv6 networks.
Note |
Certain customizations (as mentioned) are recommended to control the behavior of the VRRP group on committing the VRRP configuration on the Router. If the following customizations are not configured, then the Router seizes control of the VRRP group, and immediately assumes the role of the master virtual Router. |
/* Enter the interface configuration mode and configure an IPv6 address */
Router# interface GigabitEthernet 0/0/0/2
Router(config-if)# ipv6 address 10::1/64
Router(config-if)# no shut
/* Exit the interface configuration mode and enter the vrrp configuration mode */
Router(config-if)# exit
Router(config)# Router vrrp
/* Add the configured interface for VRRP */
Router(config-vrrp)# interface GigabitEthernet 0/0/0/2
/* CUSTOMIZATION: Configure a delay for the startup of the state machine when the interface comes up. */
Router(config-vrrp)# delay minimum 2 reload 10 */
/* Enable the IPv6 global and link local address family on the interface */
Router(config-vrrp-if)# address-family ipv6 vrrp 50
Router(config-vrrp-virtual-Router)# address linklocal autoconfig
/* CUSTOMIZATION: Disable the installation of routes for the VRRP virtual addresses. */
Router(config-vrrp-virtual-Router)# accept-mode disable
/* CUSTOMIZATION: Set a priority for the virtual Router. */
Router(config-vrrp-virtual-Router)# priority 254
/* CUSTOMIZATION: Configure a preempt delay value that controls the selection of the master virtual Router. */
Router(config-vrrp-virtual-Router)# preempt delay 15
/* CUSTOMIZATION: Configure the interval between successive advertisements by the master virtual Router. */
Router(config-vrrp-virtual-Router)#timer 4
/* CUSTOMIZATION: Configure VRRP to track an interface. */
Router(config-vrrp-virtual-Router)# track interface GigabitEthernet0/0/0/2 30
/* Commit the configuration */
Router(config-vrrp-virtual-Router)# commit
You have successfully configured VRRP for IPv6 networks.
Use the following commands to validate the configuration.
/* Validate the configuration */
Router(config-vrrp-virtual-router)# do show run interface GigabitEthernet 0/0/0/2
Fri Dec 8 14:55:48.378 IST
interface GigabitEthernet0/0/0/2
ipv6 address 10::1/64
!
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––-
Router(config-vrrp-virtual-router)# do show running-config router vrrp
...
router vrrp
interface GigabitEthernet0/0/0/2
delay minimum 2 reload 10
address-family ipv6
vrrp 50
priority 254
preempt delay 15
timer 4
track interface GigabitEthernet0/0/0/2 30
address linklocal autoconfig
accept-mode disable
!
!
!
!
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––-
Router(config-vrrp-virtual-router)# do show vrrp ipv6 interface gigabitEthernet 0/0/0/2
Fri Dec 8 14:59:25.547 IST
IPv6 Virtual Routers:
A indicates IP address owner
| P indicates configured to preempt
| |
Interface vrID Prio A P State Master addr VRouter addr
Gi0/0/0/2 50 254 P Master local
fe80::200:5eff:fe00:203
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––-
Router(config-vrrp-virtual-router)# end
Router# show vrrp detail
Fri Dec 8 15:08:36.469 IST
GigabitEthernet0/0/0/2 - IPv6 vrID 50
State is Master
2 state changes, last state change 00:18:01
State change history:
Dec 8 14:50:23.326 IST Init -> Backup Virtual IP configured
Dec 8 14:50:35.365 IST Backup -> Master Master down timer expired
Last resign sent: Never
Last resign received: Never
Virtual IP address is fe80::200:5eff:fe00:203
Virtual MAC address is 0000.5E00.0203, state is active
Master router is local
Advertise time 4 secs
Master Down Timer 12.031 (3 x 4 + (2 x 4/256))
Minimum delay 2 sec, reload delay 10 sec
Current priority 254
Configured priority 254, may preempt
minimum delay 15 secs
Tracked items: 1/1 up: 0 decrement
Object name State Decrement
GigabitEthernet0/0/0/2 Up 30
You have successfully validated VRRP for IPv6 networks.
Use the clear vrrp statistics command to clear all the software counters for the specified virtual router.
| Command or Action | Purpose |
|---|---|
|
clear vrrp statistics [interface type interface-path-id [vrid ]] Example: |
Clears all software counters for the specified virtual router.
|
VRRP enables one or more IP addresses to be assumed by a router when a failure occurs. For example, when IP traffic from a host reaches a failed router because the failed router is the default gateway, the traffic is transparently forwarded by the VRRP router that has assumed control. VRRP does not require configuration of dynamic routing or router discovery protocols on every end host. The VRRP router controlling the IP address(es) associated with a virtual router is called the master, and forwards packets sent to these IP addresses. The election process provides dynamic fail over(standby) in the forwarding responsibility should the master become unavailable. This allows any of the virtual router IP addresses on the LAN to be used as the default first hop router by end-hosts.The advantage gained from using VRRP is a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host. SNMP traps provide information of the state changes, when the virtual routers(in standby) are moved to master state or if the standby router is made master.
The snmp-server traps vrrp events command enables the Simple Network Management Protocol (SNMP) server notifications (traps) for VRRP.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
snmp-server traps vrrp events Example: |
Enables the SNMP server notifications for VRRP. |
| Step 3 |
commit |
In the event of failure of a VRRP process in one group, forced failovers in peer VRRP master router groups should be prevented. Hot restartability supports warm RP failover without incurring forced failovers to peer VRRP routers.
This section provides the following VRRP configuration examples:
This section provides the following configuration example of Router A and Router B, each belonging to three VRRP groups:
Router A:
config
interface tenGigE 0/4/0/4
ipv4 address 10.1.0.1/24
exit
router vrrp
interface tenGigE 0/4/0/4
vrrp 1 priority 120
vrrp 1 text-authentication cisco
vrrp 1 timer 3
vrrp 1 ipv4 10..0.
vrrp 5 timer 30
vrrp 5 ipv4 10..0.
preempt disable
vrrp 100 ipv4 10..0.
commit
Router B:
config
interface HundredGigE 0/4/0/4
ipv4 address 10.1.0.2/24
exit
router vrrp
interface HundredGigE 0/4/0/4
vrrp 1 priority 100
vrrp 1 text-authentication cisco
vrrp 1 timer 3
vrrp 1 ipv4 10..0.
vrrp 5 priority 200
vrrp 5 timer 30
vrrp 5 ipv4 10..0.
preempt disable
vrrp 100 ipv4 10..0.
commit
In the configuration example, each group has the following properties:
Virtual IP address is 10. .0. .
Router A will become the master for this group with priority 120.
Advertising interval is 3 seconds.
is .
is enabled.
is .
is .
Advertising interval is the default 1 second.
Preemption is .
is disabled.
The clear vrrp statistics command produces no output of its own. The command modifies the statistics given by show vrrp statistics command so that all the statistics are reset to zero.
The following section provides examples of the output of the show vrrp statistics command followed by the clear vrrp statistics command:
RP/0/RP0/CPU0:router# show vrrp statistics
show vrrp statistics
Invalid packets:
Invalid checksum: 0
Unknown/unsupported versions: 0
Invalid vrID: 10
Too short: 0
Protocol:
Transitions to Master 6
Packets:
Total received: 155
Bad TTL: 0
Failed authentication: 0
Unknown authentication: 0
Conflicting authentication: 0
Unknown Type field: 0
Conflicting Advertise time: 0
Conflicting Addresses: 0
Received with zero priority: 3
Sent with zero priority: 3
RP/0/RP0/CPU0:router# clear vrrp statistics
RP/0/RP0/CPU0:router
The following sections provide references related to VRRP.
|
Related Topic |
Document Title |
|---|---|
|
QoS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
Quality of Service Commands on Modular QoS Command Reference for Cisco NCS 6000 Series Routers |
|
Class-based traffic shaping, traffic policing, low-latency queuing, and Modified Deficit Round Robin (MDRR) |
Configuring Modular Quality of Service Congestion Management on Modular QoSConfiguration Guide for Cisco NCS 6000 Series Routers |
|
WRED, RED, and tail drop |
Configuring Modular QoS Congestion Avoidance on Modular QoSConfiguration Guide for Cisco NCS 6000 Series Routers |
|
VRRP commands |
VRRP Commands on IP Addresses and Services Command Reference for Cisco NCS 6000 Series Routers |
|
Information about user groups and task IDs |
Configuring AAA Services on System Security Configuration Guide for Cisco NCS 6000 Series Routers |
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Standards |
Title |
|---|---|
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
— |
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MIBs |
MIBs Link |
|---|---|
| — |
To locate and download MIBs, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: https://mibs.cloudapps.cisco.com/ITDIT/MIBS/servlet/index |
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RFCs |
Title |
|---|---|
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No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
— |
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Description |
Link |
|---|---|
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The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content. |
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