3.1.1.1. Virtual router

A virtual router is a logical entity managed by VRRP that acts as a default router for hosts on a shared LAN. It consists of a Virtual Router Identifier (VRID) and a set of associated IP addresses (or an address) across a common LAN. A VRRP router can backup one or more virtual routers.

The purpose of supporting multiple IP addresses within a single virtual router is for multi-netting. This is a common mechanism that allows multiple local subnet attachment on a single routing interface. Up to four virtual routers are possible on a single IP interface. The virtual routers must be in the same subnet. Each virtual router has its own VRID, state machine, and messaging instance.

3.1.1.2. IP address owner

VRRP can be configured in either the owner or non-owner mode. The owner is the VRRP router whose virtual router IP address is the same as the real interface IP address. The VRRP router configured as the owner responds to packets that are addressed to one of the IP addresses for ICMP pings, TCP connections, and others. Other virtual router instances participating in this message domain must have the same VRID configuration and cannot be configured as owner.

The 7210 SAS allows the virtual routers to be configured as non-owners of the IP address. VRRP on a router can be configured to allow non-owners to respond to ICMP echo requests when they become the virtual router in master state for the VRRP instance. Telnet and other connection-oriented protocols can also be configured for master. However, the individual application conversations (connections) will not survive a VRRP failover. A non-owner VRRP router operating as a backup will not respond to any packets addressed to any of the virtual router IP addresses.

3.1.1.3. Primary and secondary IP addresses

A primary address is an IP address selected from the set of real interface address. VRRP advertisements are always sent using the primary IP address as the source of the IP packet.

To be active, an IP interface must always have a primary IP address assigned for VRRP. Nokia routers support both primary and secondary IP addresses (multi-netting) on the IP interface. The virtual router VRID primary IP address is always the primary address on the IP interface. VRRP places this primary IP address in the source IP address field of the IP header for all VRRP messages sent on that interface.

3.1.1.4. Virtual router master state

The VRRP router that controls the IP addresses associated with a virtual router is considered to be in the master state, is the active router for the VRRP instance, and is responsible for forwarding packets sent to the VRRP IP address. An election process provides dynamic failover of the forwarding responsibility if the master becomes unavailable. In such an event, any of the virtual router IP addresses on the LAN can be used as the default first hop router by end-hosts. This capability enables a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end host.

If the active router is unavailable, each backup virtual router for the VRID compares the configured priority values to determine the master role. In case of a tie, the virtual router with the highest primary IP address becomes master.

Setting the preempt parameter to false prevents a backup virtual router configured with a better priority value from becoming master when an existing non-owner virtual router is the current master. This is determined on a first-come, first-served basis.

While master, a virtual router originates all IP packets and routes them into the LAN using the physical MAC address for the IP interface as the Layer 2 source MAC address, not the VRID MAC address. ARP packets also use the parent IP interface MAC address as the Layer 2 source MAC address and insert the virtual router MAC address in the appropriate hardware address field. VRRP messages are the only packets transmitted using the virtual router MAC address as the Layer 2 source MAC.

3.1.1.5. Virtual router backup

A new virtual router master is selected from the set of VRRP routers available to assume forwarding responsibility for a virtual router in case the current master fails.

3.1.1.6. Owner and non-owner VRRP

The owner controls the IP address of the virtual router and is responsible for forwarding packets sent to this IP address. The owner assumes the role of the master virtual router. Only one virtual router in the domain can be configured as owner. All other virtual router instances participating in this message domain must have the same VRID configured.

Priority is the most important parameter to be defined on a non-owner virtual router instance and defines the virtual router selection order in the master election process. The priority value and the preempt mode are used to determine the virtual router with the highest priority that can become the master virtual router.

The base priority is used to derive the in-use priority of the virtual router instance as modified by any optional VRRP priority control policy. VRRP priority control policies can be used to either override or adjust the base priority value depending on events or conditions within the chassis.

See VRRP non-owner accessibility for information about non-owner access parameters.

3.1.2.1. Virtual router ID (VRID)

The VRID must be configured with the same value on each virtual router associated with the redundant IP address (IP addresses). It is placed in all VRRP advertisement messages sent by each virtual router.

3.1.2.2. Priority

The priority value affects the interaction between this VRID and the same VRID of other virtual routers participating on the same LAN. A higher priority value defines a greater priority in becoming the virtual router master for the VRID. The priority value can only be configured when the defined IP address on the IP interface is different from the virtual router IP address (non-owner mode).

When the IP address on the IP interface matches the virtual router IP address (owner mode), the priority value is fixed at 255, the highest value possible. This virtual router member is considered the owner of the virtual router IP address. There can only be one owner of the virtual router IP address for all virtual router members.

The priority value 0 is reserved for VRRP advertisement message purposes. It is used to tell other virtual routers in the same VRID that this virtual router is no longer acting as master, triggering a new election process. When this happens, each backup virtual router sets its master down timer equal to the skew time value. This shortens the time until one of the backup virtual routers becomes master.

The current master virtual router must transmit a VRRP advertisement message immediately upon receipt of a VRRP message with priority set to 0. This prevents another backup from becoming master for a short period of time.

Non-owner virtual routers may be configured with a priority of 254 through 1. The default value is 100. Multiple non-owners can share the same priority value. When multiple non-owner backup virtual routers are tied (transmit VRRP advertisement messages simultaneously) in the election process, both become master simultaneously, the one with the best priority will win the election. If the priority value in the message is equal to the master local priority value, then the primary IP address of the local master and the message is evaluated as the tie breaker. The higher IP address becomes master. (The primary IP address is the source IP address of the VRRP advertisement message.)

The priority is also used to determine when to preempt the existing master. If the preempt mode value is true, VRRP advertisement messages from inferior (lower priority) masters are discarded, causing the master down timer to expire and the transition to master state.

The priority value also dictates the skew time added to the master timeout period.

3.1.2.3. IP addresses

Each virtual router participating in the same VRID should be defined with the same set of IP addresses. These are the IP addresses being used by hosts on the LAN as gateway addresses.

Multi-netting supports a total of 64 primary and secondary IP addresses on the IP interface. Up to 64 addresses can be assigned to a specific a virtual router instance.

3.1.2.4. Message interval and master inheritance

Each virtual router is configured with a message interval per VRID within which it participates. This parameter must be the same for every virtual router on the VRID.

For IPv4, the default advertisement interval is 1 s and can be configured between 1 s and 255 s 900 ms. For IPv6, the default advertisement interval is 1 s and can be configured between 1 s and 40 s 950 ms.

Note: 7210 SAS supports a minimum message interval of 1 second. It does not support use of sub-second message intervals.

As specified in the RFCs, the advertisement interval field in every received VRRP advertisement message must match the locally configured advertisement interval. If a mismatch occurs, depending on the inherit configuration, the current master's advertisement interval setting can be used to operationally override the locally configured advertisement interval setting. If the current master changes, the new master setting is used. If the local virtual router becomes master, the locally configured advertisement interval is enforced.

If a VRRP advertisement message is received with an advertisement interval set to a value different from the local value and the inherit parameter is disabled, the message is discarded without processing.

The master virtual router on a VRID uses the advertisement interval to load the advertisement timer, specifying when to send the next VRRP advertisement message. Each backup virtual router on a VRID uses the advertisement interval (with the configured local priority) to derive the master down timer value.

VRRP advertisements messages that are fragmented, or contain IP options (IPv4) or extension headers (IPv6) require a longer message interval.

3.1.2.5. Skew time

The skew time is used to add a time period to the master down interval. This is not a configurable parameter. It is derived from the current local priority of the virtual router VRID. To calculate the skew time, the virtual router evaluates the following formula:

The higher the priority value, the smaller the skew time will be. This means that virtual routers with a lower priority will transition to master slower than virtual routers with higher priorities.

3.1.2.6. Master down interval

The master down interval is a calculated value used to load the master down timer. When the master down timer expires, the virtual router enters the master state. To calculate the master down interval, the virtual router evaluates the following formula:

Master Down Interval = (3 x Operational Advertisement Interval) + Skew Time

The operational advertisement interval is dependent upon the state of the inherit parameter. When the inherit parameter is enabled, the operational advertisement interval is derived from the current master advertisement interval field in the VRRP advertisement message. When inherit is disabled, the operational advertisement interval must be equal to the locally configured advertisement interval.

The master down timer is only operational when the local virtual router is operating in backup mode.

3.1.2.7. Preempt mode

Preempt mode is a true or false configured value which controls whether a specific backup virtual router preempts a lower priority master. The IP address owner will always become master when available. Preempt mode cannot be set to false on the owner virtual router. The default value for preempt mode is true.

When preempt mode is true, the advertised priority from the incoming VRRP advertisement message from the current master is compared to the local configured priority. If the local priority is higher, the received VRRP advertisement message is discarded. This will result in the eventual expiration of the master down timer causing a transition to the master state. If the received priority is equal to the local priority, the message is not discarded and the current master will not be discarded. Note that when in the backup state, the received primary IP address is not part of the decision to preempt and is not used as a tie breaker when the received and local priorities are equal.

When preempt is enabled, the virtual router instance overrides any non-owner master with an in-use message priority value less than the virtual router instance in-use priority value. If preempt is disabled, the virtual router only becomes master if the master down timer expires before a VRRP advertisement message is received from another virtual router.

3.1.2.8. VRRP message authentication

The authentication type parameter defines the type of authentication used by the virtual router in VRRP advertisement message authentication. VRRP message authentication is applicable to IPv4 only. The current master uses the configured authentication type to indicate any egress message manipulation that must be performed in conjunction with any supporting authentication parameters before transmitting a VRRP advertisement message. The configured authentication type value is transmitted in the message authentication type field with the appropriate authentication data field filled in. Backup routers use the authentication type message field value in interpreting the contained authentication data field within received VRRP advertisement messages.

VRRP supports two message authentication methods that provide different degrees of security. The supported authentication types are:

3.1.2.9. Authentication data

This feature is different from the VRRP advertisement message field with the same name. This is any required authentication information that is pertinent to the configured authentication type. The type of authentication data used for each authentication type is listed in the following table.

3.1.2.10. Virtual MAC address

On 7210 SAS, the MAC address is not configurable. 7210 SAS derives the MAC address to use from the VRID assigned as defined in the standard.

3.1.2.11. VRRP advertisement message IP address list verification

VRRP advertisement messages contain an IP address count field that indicates the number of IP addresses listed in the sequential IP address fields at the end of the message.

The implementation always logs mismatching events. The decision on where and whether to forward the generated messages depends on the configuration of the event manager.

To facilitate the sending of mismatch log messages, each virtual router instance keeps the mismatch state associated with each source IP address in the VRRP master table. Whenever the state changes, a mismatch log message is generated indicating the source IP address within the message, the mismatch or match event and the time of the event.

With secondary IP address support, multiple IP addresses may be found in the list and it should match the IP address on the virtual router instance. Owner and non-owner virtual router instances have the supported IP addresses explicitly defined, making mismatched supported IP address within the interconnected virtual router instances a provisioning issue.

3.1.2.12. IPv6 virtual router instance operationally up

If the IPv6 virtual router is configured with a minimum of one link-local backup address, the router advertisement of the parent interface must be configured to use the virtual MAC address for the virtual router to be considered operationally up.

3.1.2.13. Policies

Policies can be configured to control VRRP priority with the virtual router instance. VRRP priority control policies can be used to override or adjust the base priority value depending on events or conditions within the chassis.

The policy can be associated with more than one virtual router instance. The priority events within the policy override or diminish the base priority dynamically affecting the in-use priority. As priority events clear in the policy, the in-use priority can eventually be restored to the base priority value.

Policies can only be configured in the non-owner VRRP context. For non-owner virtual router instances, if policies are not configured, then the base priority is used as the in-use priority.

3.2.4.1. Priority event hold-set timers

Hold-set timers are used to dampen the effect of a flapping event. A flapping event is where the event continually transitions between clear and set. The hold-set value is loaded into a hold-set timer that prevents a set event from transitioning to the cleared state until it expires.

Each time an event transitions between cleared and set, the timer is loaded and begins to count down to zero. If the timer reaches zero, the event will be allowed to enter the cleared state again. Entering the cleared state is always dependent on the object controlling the event conforming to the requirements defined in the event. It is possible, on some event types, to have a further set action reload the hold-set timer. This extends the amount of time that must expire before entering the cleared state.

See LAG degrade priority event for an example of a hold-set timer setting.

3.2.4.2. Port down priority event

The port down priority event is tied to either a physical port or a SONET/SDH channel. The port or channel operational state is evaluated to determine a port down priority event or event clear.

When the port or channel operational state is up, the port down priority event is considered false or cleared. When the port or channel operational state is down, the port down priority event is considered true or set.

3.2.4.3. LAG degrade priority event

The LAG degrade priority event is tied to an existing Link Aggregation Group (LAG). The LAG degrade priority event is conditional to percentage of available port bandwidth on the LAG. Multiple bandwidth percentage thresholds may be defined, each with its own priority value.

If the LAG transitions from one threshold to the next, the previous threshold priority value is subtracted from the total delta sum while the new threshold priority value is added to the sum. The new sum is then subtracted from the base priority and compared to the delta in-use priority limit to derive the new in-use priority on the virtual router instance.

The following example illustrates a LAG priority event and interaction with the hold-set timer in changing the in-use priority.

The following state and timer settings are used for the LAG events listed in the following table:

3.2.4.4. Host unreachable priority event

The host unreachable priority event creates a continuous ping task that is used to test connectivity to a remote host. The path to the remote host and the remote host must be capable and configured to accept ICMP echo request and replies for the ping to be successful.

The ping task is controlled by interval and size parameters that define how often the ICMP request messages are transmitted and the size of each message. A historical missing reply parameter defines when the ping destination is considered unreachable.

When the host is unreachable, the host unreachable priority event is considered true or set. When the host is reachable, the host unreachable priority event is considered false or cleared.

3.2.4.5. Route unknown priority event

The route unknown priority event defines a task that monitors the existence of a specific route prefix in the system routing table.

The route monitoring task can be constrained by a condition that allows a prefix that is less specific than the defined prefix to be considered as a match. The source protocol can be defined to indicate the protocol the installed route must be populated from. To further define match criteria when multiple instances of the route prefix exist, an optional next hop parameter can be defined.

When a route prefix exists within the active route table that matches the defined match criteria, the route unknown priority event is considered false or cleared. When a route prefix does not exist within the active route table matching the defined criteria, the route unknown priority event is considered true or set.