VRRP (virtual router redundancy protocol)

VRRP (Virtual Router Redundancy Protocol)
VRRP (Virtual Router Redundancy Protocol) is a computer networking protocol that provides for
automatic assignment of available Internet Protocol (IP) routers to participating hosts. This increases the
availability and reliability of routing paths via automatic default gateway selections on an IP subnetwork.
The Virtual Router Redundancy Protocol (VRRP) eliminates the single point of failure inherent in the
static default routed environment. VRRP specifies an election protocol that dynamically assigns
responsibility for a virtual router (a VPN 3000 Series Concentrator cluster) to one of the VPN
Concentrators on a LAN. The VRRP VPN Concentrator that controls the IP address(es) associated with a
virtual router is called the Master, and forwards packets sent to those IP addresses. When the Master
becomes unavailable, a backup VPN Concentrator takes the place of the Master.
VRRP (Virtual Router Redundancy Protocol) Points to Remember:
1. Open Standard Protocol (1999)
2. Hello Timer 1 sec
3. Hold Timer 3 sec
4. It use IP Protocol no 112
5. It sends multicast hellos on 224.0.0.18
6. Default Preempt enable
7. Default Priority 100
8. No inbuilt Track command
9. Default decrement in priority using external track = 10
10. VRRP Mac 000.5e00.01xx (xx is group ID)
11. It supports two types of authentication MD-5, Plain Txt.
Figure 1 Basic VRRP Terminology

VRRP Roles
(i) Master
(ii) Backup
Master – A router which gives the reply of ARP request of clients for gateway.
Master Requirement –
(i) High Priority
(ii) Higher IP
Load balancing is Possible using multiple groups like HSRP
Group ID – 1 to 255
Restrictions for VRRP
VRRP is designed for use over multiaccess, multicast, or broadcast capable Ethernet LANs. VRRP is not
intended as a replacement for existing dynamic protocols.
VRRP is supported on Ethernet, Fast Ethernet, Bridge Group Virtual Interface (BVI), and Gigabit Ethernet
interfaces, and on Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs), VRF-aware
MPLS VPNs, and VLANs.
Because of the forwarding delay that is associated with the initialization of a BVI interface, you must
configure the VRRP advertise timer to a value equal to or greater than the forwarding delay on the BVI
interface. This setting prevents a VRRP router on a recently initialized BVI interface from unconditionally
taking over the master role. Use the bridge forward-time command to set the forwarding delay on the
BVI interface. Use the vrrp timers advertise command to set the VRRP advertisement timer.
Enhanced Object Tracking (EOT) is not stateful switchover (SSO)-aware and cannot be used with VRRP in
SSO mode.
VRRP Operation
There are several ways a LAN client can determine which router should be the first hop to a particular
remote destination. The client can use a dynamic process or static configuration. Examples of dynamic
router discovery are as follows:
1. Proxy ARP— The client uses Address Resolution Protocol (ARP) to get the destination it wants to
reach, and a router will respond to the ARP request with its own MAC address.
2. Routing protocol— The client listens to dynamic routing protocol updates (for example, from
Routing Information Protocol [RIP]) and forms its own routing table.

3. ICMP Router Discovery Protocol (IRDP) 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.
VRRP can solve the static configuration problem. 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.
VRRP is supported on Ethernet, Fast Ethernet, BVI, and Gigabit Ethernet interfaces, and on MPLS VPNs,
VRF-aware MPLS VPNs, and VLANs.
Figure 2 LAN topology in which VRRP is configured. In this example, Routers A, B, and C are VRRP routers
(routers running VRRP) that comprise a virtual router. The IP address of the virtual router is the same as that
configured for the Ethernet interface of Router A (10.0.0.1)

Multiple Virtual Router Support
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:
1. Router processing capability
2. Router memory capability
3. 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 virtual router and as a backup for one or more virtual routers.
VRRP Router Priority and Preemption
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 virtual router master fails.
If a VRRP router owns the IP address of the virtual router and the IP address of the physical interface,
this router will function as a virtual router master.
Priority also determines if a VRRP router functions as a virtual router backup and the order of
ascendancy to becoming a virtual router master if the virtual router master fails. You can configure the
priority of each virtual router backup with a value of 1 through 254 using the vrrp priority command.
For example, if Router A, the virtual router master in a LAN topology, fails, an election process takes
place to determine if virtual router backups 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 virtual router master
because it has the higher priority. If Routers B and C are both configured with the priority of 100, the
virtual router backup with the higher IP address is elected to become the virtual router master.
By default, a preemptive scheme is enabled whereby a higher priority virtual router backup that
becomes available takes over for the virtual router backup that was elected to become virtual router
master. You can disable this preemptive scheme using the no vrrp preempt command. If preemption is
disabled, the virtual router backup that is elected to become virtual router master remains the master
until the original virtual router master recovers and becomes master again.
VRRP Advertisements
The virtual router master sends VRRP advertisements to other VRRP routers in the same group. The
advertisements communicate the priority and state of the virtual router master. 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.

Although the VRRP protocol as per RFC 3768 does not support millisecond timers, Cisco routers allow
you to configure millisecond timers. You need to manually configure the millisecond timer values on
both the primary and the backup routers. The master advertisement value displayed in the show vrrp
command output on the backup routers is always 1 second because the packets on the backup routers
do not accept millisecond values.
You must use millisecond timers where absolutely necessary and with careful consideration and testing.
Millisecond values work only under favorable circumstances, and you must be aware that the use of the
millisecond timer values restricts VRRP operation to Cisco devices only.
VRRP Object Tracking
Object tracking is an independent process that manages creating, monitoring, and removing tracked
objects such as the state of the line protocol of an interface. Clients such as the Hot Standby Router
Protocol (HSRP), Gateway Load Balancing Protocol (GLBP), and VRRP register their interest with specific
tracked objects and act when the state of an object changes.
Each tracked object is identified by a unique number that is specified on the tracking CLI. Client
processes such as VRRP use this number to track a specific object.
The tracking process periodically polls the tracked objects and notes any change of value. The changes in
the tracked object are communicated to interested client processes, either immediately or after a
specified delay. The object values are reported as either up or down.
VRRP object tracking gives VRRP access to all the objects available through the tracking process. The
tracking process allows you to track individual objects such as a the state of an interface line protocol,
state of an IP route, or the reachability of a route.
VRRP provides an interface to the tracking process. Each VRRP group can track multiple objects that may
affect the priority of the VRRP device. You specify the object number to be tracked and VRRP is notified
of any change to the object. VRRP increments (or decrements) the priority of the virtual device based on
the state of the object being tracked.
VRRP Authentication
VRRP ignores unauthenticated VRRP protocol messages. The default authentication type is text
authentication.
You can configure VRRP text authentication, authentication using a simple MD5 key string, or MD5 key
chains for authentication.
MD5 authentication provides greater security than the alternative plain text authentication scheme.
MD5 authentication allows each VRRP group member to use a secret key to generate a keyed MD5 hash

of the packet that is part of the outgoing packet. A keyed hash of an incoming packet is generated and if
the generated hash does not match the hash within the incoming packet, the packet is ignored.
The key for the MD5 hash can either be given directly in the configuration using a key string or supplied
indirectly through a key chain.
A router will ignore incoming VRRP packets from routers that do not have the same authentication
configuration for a VRRP group. VRRP has three authentication schemes:
1. No authentication
2. Plain text authentication
3. MD5 authentication
VRRP packets will be rejected in any of the following cases:
1. The authentication schemes differ on the router and in the incoming packet.
2. MD5 digests differ on the router and in the incoming packet.
3. Text authentication strings differ on the router and in the incoming packet.
Customizing VRRP
Customizing the behavior of VRRP is optional. Be aware that as soon as you enable a VRRP group, that
group is operating. It is possible that if you first enable a VRRP group before customizing VRRP, the
router could take over control of the group and become the virtual router master before you have
finished customizing the feature. Therefore, if you plan to customize VRRP, it is a good idea to do so
before enabling VRRP.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip address ip-address mask
5. vrrp group description text
6. vrrp group priority level
7. vrrp group preempt [delay minimum seconds]
8. vrrp group timers advertise [msec] interval
9. vrrp group timers learn
10. exit
11. no vrrp sso

Enabling VRRP
SUMMARY STEPS
1. enable
5. vrrp group ip ip-address [secondary]
6. end
7. show vrrp [brief] | group]
8. show vrrp interface type number [brief]
Disabling a VRRP Group on an Interface
Disabling a VRRP group on an interface allows the protocol to be disabled, but the configuration to be
retained. This ability was added with the introduction of the VRRP MIB, RFC 2787, Definitions of
Managed Objects for the Virtual Router Redundancy Protocol .
You can use a Simple Network Management Protocol (SNMP) management tool to enable or disable
VRRP on an interface. Because of the SNMP management capability, the vrrp shutdown command was
introduced to represent a method via the command line interface (CLI) for VRRP to show the state that
had been configured using SNMP.
When the show running-config command is entered, you can see immediately if the VRRP group has
been configured and set to enabled or disabled. This is the same functionality that is enabled within the
MIB.
The no form of the command enables the same operation that is performed within the MIB. If the vrrp
shutdown command is specified using the SNMP interface, then entering the no vrrp shutdown
command reenables the VRRP group.
SUMMARY STEPS
1. enable
5. vrrp group shutdown

Configuring VRRP Object Tracking
(Note: If a VRRP group is the IP address owner, its priority is fixed at 255 and cannot be reduced through
object tracking.)
SUMMARY STEPS
1. enable
3. track object-number interface type number {line-protocol | ip routing}
5. vrrp group ip ip-address
6. vrrp group priority level
7. vrrp group track object-number [decrement priority]
8. end
9. show track [object-number]
Configuring VRRP MD5 Authentication Using a Key String
(Note: Interoperability with vendors that may have implemented the RFC 2338 method is not enabled.
Text authentication cannot be combined with MD5 authentication for a VRRP group at any one time.
When MD5 authentication is configured, the text authentication field in VRRP hello messages is set to all
zeroes on transmit and ignored on receipt, provided the receiving router also has MD5 authentication
enabled.)
SUMMARY STEPS
1. enable
4. ip address ip-address mask [secondary]
5. vrrp group priority priority
6. vrrp group authentication md5 key-string [0 | 7] key-string [timeout seconds]
7. vrrp group ip [ip-address[secondary]]
8. Repeat Steps 1 through 7 on each router that will communicate.
9. end
Configuring VRRP MD5 Authentication Using a Key Chain
Perform this task to configure VRRP MD5 authentication using a key chain. Key chains allow a different
key string to be used at different times according to the key chain configuration. VRRP will query the
appropriate key chain to obtain the current live key and key ID for the specified key chain.

SUMMARY STEPS
1. enable
3. key chain name-of-chain
4. key key-id
5. key-string string
6. exit
9. vrrp group priority priority
10. vrrp group authentication md5 key-chain key-chain
11. vrrp group ip [ip-address[secondary]]
13. end
Verifying the VRRP MD5 Authentication Configuration
SUMMARY STEPS
1. show vrrp
2. debug vrrp authentication
Configuring VRRP Text Authentication
Before You Begin
Interoperability with vendors that may have implemented the RFC 2338 method is not enabled. Text
authentication cannot be combined with MD5 authentication for a VRRP group at any one time. When
MD5 authentication is configured, the text authentication field in VRRP hello messages is set to all zeros
on transmit and ignored on receipt, provided the receiving router also has MD5 authentication enabled.
SUMMARY STEPS
1. enable
3. terminal interface type number
5. vrrp group authentication text text-string
6. vrrp group ip ip-address
8. end

Enabling the Router to Send SNMP VRRP Notifications
The VRRP MIB supports SNMP Get operations, which allow network devices to get reports about VRRP
groups in a network from the network management station.
Enabling VRRP MIB trap support is performed through the CLI, and the MIB is used for getting the
reports. A trap notifies the network management station when a router becomes a Master or backup
router. When an entry is configured from the CLI, the RowStatus for that group in the MIB immediately
goes to the active state.
SUMMARY STEPS
1. enable
3. snmp-server enable traps vrrp
4. snmp-server host host community-string vrrp
VRRP Benefits
 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 255 virtual routers (VRRP groups) on a router physical 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 virtual router backup that has taken over for
a failing virtual router master with a higher priority virtual router backup that has become available.

 Authentication
VRRP message digest 5 (MD5) algorithm authentication protects against VRRP-spoofing software and
uses the industry-standard MD5 algorithm for improved reliability and security.
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 assigned VRRP the IP protocol number 112.
VRRP Object Tracking
VRRP object tracking provides a way to ensure the best VRRP router is the virtual router master for the
group by altering VRRP priorities to the status of tracked objects such as the interface or IP route states.
Example for VRRP
Figure 3 VRRP Topology

R1 (config) #int fa0/0
R1 (config-if) #ip add 192.168.101.2 255.255.255.0
R1 (config-if) #no shut
R1 (config-if) #int s0/0
R1 (config-if) #ip add 192.168.1.1 255.255.255.0
R1 (config) #router ei 100
R1 (config-router) #no auto
R1 (config-router) #network 0.0.0.0
Ho (config) #int fa0/0
Ho (config-if) #ip add 192.168.102.1 255.255.255.0
Ho (config-if) #no shut
Ho (config-if) #int s0/0
Ho (config-if) #int s0/1
Ho (config-if) #router ei 100
Ho (config-router) #no auto
Ho (config-router) #network 0.0.0.0
R2 (config-if) #ip add 192.168.101.3 255.255.255.0
R2 (config-if) #int s0/0
R2 (config-if) #ip add 192.168.2.2 255.255.255.0
R2 (config-if) #router ei 100
R2 (config-router) #no auto
R2 (config-router) #network 0.0.0.0
Ho #sh ip route
R1#sh ip int br
R2#sh ip int br
Now we will provide the IP add to the PC, which is 192.168.101.10. And computer Gateway would
192.168.101.1.
R1 (config-if) #vrrp 1 ip 192.168.101.1

Now we can see the R2 will become Master and R1 will go into Backup, because R2s IP address is higher
and by default preemption is enabled in VRRP.
Comp# tracert –d 192.168.102.1
Here we can see all the data is going via R2. Because R2 is Master
R2 (config-if) #shut
Now R1 will become Master
All the traffic going via R1
Once R2s Fa0/0 comes up, it will become once again Master
R1#sh vrrp
Default Hello timer 1 sec
Hold – 3 sec
Preempt – enabled by default
Default Priority 100
Virtual Mac 0000.5e00.0101
Now if the WAN link goes down
R2 (config) #int s0/0
First data will reach R2 and then R1
R1 will not become master here in case of serial link failure. For that we need to enable Track
command.

R2 (config-if) #int fa0/0
R2 (config-if) #vrrp 1 track?
R2 (config-if) #exit
R2 (config) #track ?
1 to 500
R2 (config) #track 1 ?
R2 (config) #track 1 int s0/0 ?
R2 (config) #track 1 int s0/0 line protocol
R2 (config-if) #vrrp 1 track 1
R2#sh vrrp
Track obj 1 state up decrement 10
Data is going via R2
R2#sh vrrp
Priority 90
All data will go via R1
Load Balancing
For load balancing we will create one more group
Till now for Group 1, Master is R2
R1 (config-if) #vrrp 2 priority 101
R1 (config) # track 1 int s0/0 line protocol
R1 (config-if) #vrrp 2 track 1
R2#sh vrrp

Group 1 Master, Group 2 Backup
R1#sh vrrp
Group 1 Backup, Group 2 Master
R2 #sh vrrp
R1#sh vrrp
For load balancing if we provide clients default gateway is 192.168.101.1 then the data will go via R2, if
we provide clients gateway 192.168.101.4 then data will go via R1.

VRRP (virtual router redundancy protocol)

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