Configuring Stateful Interchassis Redundancy

The Stateful Interchassis Redundancy feature enables you to configure pairs of devices to act as backups for each other.

This module describes conceptual information about and tasks for configuring stateful interchassis redundancy.

Prerequisites for Stateful Interchassis Redundancy

All application redundancy configurations, including Network Address Translation (NAT) rules that have redundancy group associations and mapping IDs, must be identical on both devices, or NAT sessions will not be synchronized between devices and NAT redundancy will not work.

Restrictions for Stateful Interchassis Redundancy

  • By default, Network Address Translation (NAT) high availability (inter and intrabox) does not replicate HTTP sessions to the standby device. To replicate HTTP sessions on the standby device during a switchover, you must configure the ip nat switchover replication http command.

  • During NAT payload translations with certain applications, there can be IP addresses in the payload that require NAT translation. The application-level gateway (ALG) for that specific application parses the packet for these IP addresses, NAT translates these addresses, and the ALG writes the translated addresses back into the packet.

    Fixup denotes the writing of the translated IP address back into the packet. The write back of data can change the length of a packet, which results in the adjustment of the packet's TCP sequence (SEQ) or acknowledgment (ACK) values by NAT for the life of the TCP connection. NAT writes the new TCP SEQ/ACK values into the packet during SEQ/ACK fixup.

    For example, during a TCP ALG session, SEQ/ACK values may require fixup with mainly ASCII applications such as Domain Name System (DNS), FTP/FTP64, H.323, Real Time Streaming Protocol (RTSP), and Session Initiation Protocol (SIP). This SEQ/ACK adjustment information gets associated with the NAT session and is synchronized to the standby device periodically.

    During a stateful switchover, if the SEQ/ACK information is not completely synchronized to the new active device it is likely that the TCP connection would be reset by endpoints of the application.

  • Stateful interchassis redundancy cannot coexist with intrachassis redundancy, including software redundancy.

  • In Service Software Upgrade (ISSU) is not supported.

  • When changing the paired-address-pooling, bulk port-allocation, or NAT mode settings the following steps must be followed:

    1. Shutdown the redundancy group and NAT interfaces on the standby device using the shutdown command. Clear NAT sessions on the standby device after shutting down the redundancy group.

    2. Change the paired-address-pooling, bulk port-allocation, or NAT mode on the standby device first and then on the active device.

    3. Configure the no shutdown command for the redundancy group and NAT interfaces on the standby device.

  • In a NAT Stateful Interchassis Redundancy configuration, it is mandatory that both peers use the same inside and outside NAT interfaces. If the interfaces are not same, it can lead to duplicate NAT entries.

  • The following translations are not synchronized to the standby router :

    • Translations created based on an interface overload rule

    • ICMP requests


Note

For a standalone NAT router, shut down the NAT interfaces before you make a configuration change.

Information About Stateful Interchassis Redundancy

Stateful Interchassis Redundancy Overview

You can configure the Stateful Interchassis Redundancy feature to determine the active device from a group of devices, based on a number of failover conditions. When a failover occurs, the standby device seamlessly takes over, starts performing traffic forwarding services, and maintains a dynamic routing table.


Note
Manually shutting down the control or data interface link on an active NAT router results in traffic outage as the NAT router never transitions to active state.

Stateful Interchassis Redundancy Operation

You can configure pairs of devices to act as hot standbys for each other. Redundancy is configured on an interface basis. Pairs of redundant interfaces are known as redundancy groups (RGs). Redundancy occurs at an application level and does not require a complete physical failure of the interface or device for a switchover of the application to occur. When a switchover occurs, the application activity continues to run seamlessly on the redundant interface.

The figure below depicts an active/standby load-sharing scenario. The figure shows how an RG is configured for a pair of devices that has one outgoing interface. Group A on Router 1 is the active RG and Group A on Router 2 is the standby RG.

Redundant devices are joined by a configurable control link and a data synchronization link. The control link is used to communicate the status of devices. The data synchronization link is used to transfer stateful information from Network Address Translation (NAT) and the firewall and synchronize the stateful database. The pairs of redundant interfaces are configured with the same unique ID number known as the redundant interface identifier (RII).

Figure 1. Redundancy Group Configuration—One Outgoing Interface

The status of redundancy group members is determined through the use of hello messages sent over the control link. The software considers either device not responding to a hello message within a configurable amount of time to be a failure and initiates a switchover. For the software to detect a failure in milliseconds, control links run the failover protocol that is integrated with the Bidirectional Forwarding Detection (BFD) protocol. You can configure the following parameters for hello messages:

  • Hello time—Interval at which hello messages are sent.
  • Hold time—Amount of time before which the active or standby device is declared to be down.

The hello time defaults to 3 seconds to align with the Hot Standby Router Protocol (HSRP), and the hold time defaults to 10 seconds. You can also configure these timers in milliseconds by using the timers hellotime msec command.

To determine the pairs of interfaces that are affected by the switchover, you must configure a unique ID for each pair of redundant interfaces. This ID is known as the RII that is associated with the interface.

A switchover to the standby device can occur when the priority setting that is configured on each device changes. The device with the highest priority value acts as the active device. If a fault occurs on either the active or standby device, the priority of the device is decremented by a configurable amount known as the weight. If the priority of the active device falls below the priority of the standby device, a switchover occurs and the standby device becomes the active device. This default behavior can be overridden by disabling the preemption attribute for the RG. You can also configure each interface to decrease the priority when the Layer 1 state of the interface goes down. The priority that is configured overrides the default priority of an RG.

Each failure event that causes a modification of an RG priority generates a syslog entry that contains a time stamp, the RG that was affected, the previous priority, the new priority, and a description of the failure event cause.

A switchover also can occur when the priority of a device or interface falls below a configurable threshold level.

A switchover to the standby device occurs under the following circumstances:

  • Power loss or a reload occurs on the active device (including reloads).
  • The run-time priority of the active device goes below that of the standby device (with preempt configured).
  • The run-time priority of the active device goes below that of the configured threshold.
  • The redundancy group on the active device is reloaded manually. Use the redundancy application reload group rg-number command for a manual reload.

Associations with Firewalls and NAT

Firewalls use the association of the redundancy group with a traffic interface.

Network Address Translation (NAT) associates the redundancy group with a mapping ID.

LAN-LAN Topology

The figure below shows the LAN-LAN topology. In a LAN-LAN topology, all participating devices are connected to each other through LAN interfaces on both the inside and the outside. In this scenario, traffic is often directed to the correct firewall if static routing is configured on the upstream or downstream devices to an appropriate virtual IP address. This plaform participate in dynamic routing with upstream or downstream devices. The dynamic routing configuration supported on LAN-facing interfaces must not introduce a dependency on the routing protocol convergence; otherwise, fast failover requirements will not be met.

Figure 2. LAN-LAN Topology

How to Configure Stateful Interchassis Redundancy

Configuring the Control Interface Protocol

The configuration for the control interface protocol consists of the following elements:

  • Authentication information

  • Group name

  • Hello time

  • Hold time

  • Protocol instance

  • Use of the bidirectional forwarding direction (BFD) protocol

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. redundancy
  4. mode none
  5. application redundancy
  6. protocol number
  7. name instance-name
  8. timers hellotime [msec ] number holdtime [msec ] number
  9. authentication {text string | md5 key-string [0 | 7 ] key | md5 key-chain key-chain-name }
  10. bfd
  11. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

redundancy

Example:

Device(config)# redundancy

Enters redundancy configuration mode.

Step 4

mode none

Example:

Device(config-red)# mode none

Sets the redundancy mode to none, which is required for this feature.

Step 5

application redundancy

Example:

Device(config-red)# application redundancy

Enters redundancy application configuration mode.

Step 6

protocol number

Example:

Device(config-red-app)# protocol 4

Specifies the protocol instance that will be attached to a control interface, and enters redundancy application protocol configuration mode.

Step 7

name instance-name

Example:

Device(config-red-app-prot)# name rg1

(Optional) Specifies an optional alias for the protocol instance.

Step 8

timers hellotime [msec ] number holdtime [msec ] number

Example:

Device(config-red-app-prot)# timers hellotime 3 holdtime 10
Specifies the interval between hello messages sent and the time before a device is declared to be down.

  • The default time for hello time is 3 seconds and for hold time is 10 seconds.

Step 9

authentication {text string | md5 key-string [0 | 7 ] key | md5 key-chain key-chain-name }

Example:

Device(config-red-app-prot)# authentication text password

Specifies authentication information.

Step 10

bfd

Example:

Device(config-red-app-prot)# bfd
(Optional) Enables the integration of the failover protocol running on the control interface with the BFD protocol to achieve failure detection in milliseconds.

  • BFD is enabled by default.

Step 11

end

Example:

Device(config-red-app-prot)# end

Exits redundancy application protocol configuration mode and enters privileged EXEC mode.

Tracking a Redundant Traffic Interface

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. track object-number interface type number {line-protocol | ip | routing | ipv6 routing}
  4. redundancy
  5. application redundancy
  6. group {1 | 2}
  7. track object-number [decrement number | shutdown]
  8. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

track object-number interface type number {line-protocol | ip | routing | ipv6 routing}

Example:

Device(config)# track 44 interface Gi0/1/5 line-protocol0

Tracks the interface and enters tracking configuration mode of a router. Tracks the state of the interface line protocol before failing over to a redundant traffic interface in the group.

Step 4

redundancy

Example:

Device(config-track)# redundancy

Enters redundancy configuration mode.

Step 5

application redundancy

Example:

Device(config-trac-red)# application redundancy

Enters redundancy application configuration mode.

Step 6

group {1 | 2}

Example:

Device(config-track-red-app)# group 1

Specifies the redundancy group instance and enters redundancy application group configuration mode.

Step 7

track object-number [decrement number | shutdown]

Example:

Device(config-trac-red-app-grp)# track 44 decrement 20
Specifies the amount by which the priority of a redundancy group will be decremented if an event occurs.

  • You can track multiple objects that influence the priority of the redundancy group.

Step 8

end

Example:

Device(config-if)# end

Exits interface configuration mode and enters privileged EXEC mode.

Configuring a Redundancy Group

Redundancy groups consist of the following configuration elements:

  • The amount by which the priority will be decremented for each object.

  • Faults (objects) that will decrement the priority.

  • Failover priority.

  • Failover threshold.

  • Group instance.

  • Group name.

  • Initialization delay timer.

  • The interface that is associated with the redundancy group (RG).

  • The interface that is used as the control interface.

  • The interface that is used as the data interface.

  • The redundancy interface identifier (RII) number of the RG interface.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. redundancy
  4. application redundancy
  5. group {1 | 2}
  6. name group-name
  7. preempt
  8. priority number failover-threshold number
  9. timers delay seconds [reload seconds]
  10. control interface-name protocol instance
  11. data interface-name
  12. To create another redundancy group, repeat Steps 3 through 12.
  13. end
  14. configure terminal
  15. interface type number
  16. redundancy group number ip address exclusive [decrement number]
  17. redundancy rii number
  18. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

redundancy

Example:

Device(config)# redundancy

Enters redundancy configuration mode.

Step 4

application redundancy

Example:

Device(config-red)# application redundancy

Enters redundancy application configuration mode.

Step 5

group {1 | 2}

Example:

Device(config-red-app)# group 1

Specifies the redundancy group instance and enters redundancy application group configuration mode.

Step 6

name group-name

Example:

Device(config-red-app-grp)# name rg1

(Optional) Specifies an optional alias for the protocol instance.

Step 7

preempt

Example:

Device(config-red-app-grp)# preempt

Enables preemption on the group and enables the standby device to preempt the active device regardless of which device has higher priority.

Step 8

priority number failover-threshold number

Example:

Device(config-red-app-grp)# priority 120 failover-threshold 80

Specifies the initial priority and failover threshold for the redundancy group.

Step 9

timers delay seconds [reload seconds]

Example:

Device(config-red-app-grp)# timers delay 10 reload 20

Specifies the amount of time by which the redundancy group will delay role negotiations that start after a fault occurs or after the system is reloaded.

Step 10

control interface-name protocol instance

Example:

Device(config-red-app-grp)# control GigabitEthernet0/1/0 protocol 1
Specifies the control interface that is used by the redundancy group.

  • This interface is also associated with an instance of the control interface protocol.

Step 11

data interface-name

Example:

Device(config-red-app-grp)# data GigabitEthernet0/1/2

Specifies the data interface that is used by the redundancy group.

Step 12

To create another redundancy group, repeat Steps 3 through 12.

—

Step 13

end

Example:

Device(config-red-app-grp)# end

Exits redundancy application group configuration mode and enters privileged EXEC mode.

Step 14

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 15

interface type number

Example:

Device(config)# interface gigabitethernet 0/0/1

Selects an interface to associate with the redundancy group and enters interface configuration mode.

Step 16

redundancy group number ip address exclusive [decrement number]

Example:

Device(config-if)# redundancy group 1 ip 10.10.1.1 exclusive decrement 20

Associates the interface with the redundancy group identified by the number argument.

Step 17

redundancy rii number

Example:

Device(config-if)# redundancy rii 40
Specifies a number for the RII associated with this interface.

  • This number must match the RII of the other interface in the redundancy group.

Step 18

end

Example:

Device(config-if)# end

Exits interface configuration mode and enters privileged EXEC mode.

Configuring a Redundant Traffic Interface

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. ip address ip-address mask
  5. ip nat outside
  6. ip virtual-reassembly
  7. negotiation auto
  8. redundancy rii number
  9. redundancy group number ip address exclusive [decrement number]
  10. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

interface type number

Example:

Device(config)# interface gigabitethernet 0/1/5

Configures an interface and enters interface configuration mode.

Step 4

ip address ip-address mask

Example:

Device(config-if)# ip address 10.1.1.2 255.0.0.0

Sets a primary or secondary IP address for an interface.

Step 5

ip nat outside

Example:

Device(config-if)# ip nat outside

Configures the outside interface for IP address translation.

Step 6

ip virtual-reassembly

Example:

Device(config-if)# ip virtual-reassembly

Enables Virtual Fragmentation Reassembly (VFR) on an interface.

Step 7

negotiation auto

Example:

Device(config-if)# negotiation auto

Enables the autonegotiation protocol to configure the speed, duplex, and automatic flow control of the Gigabit Ethernet interface.

Step 8

redundancy rii number

Example:

Device(config-if)# redundancy rii 200
Specifies a number for the redundancy interface identifier (RII) that is associated with this interface.

  • This number must match the RII of the other interface in the redundancy group.

Step 9

redundancy group number ip address exclusive [decrement number]

Example:

Device(config-if)# redundancy group 1 ip 10.1.1.200 exclusive decrement 10

Associates the interface with the redundancy group identified by the number argument.

Step 10

end

Example:

Device(config-if)# end

Exits interface configuration mode and enters privileged EXEC mode.

Configuring NAT with Stateful Interchassis Redundancy

You must use a mapping ID to associate Network Address Translation (NAT) with a redundancy group.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length}
  4. ip nat inside source list {{access-list-number | access-list-name} | route-map name} pool name [redundancy redundancy-id [mapping-id map-id | overload | reversible | vrf name]]
  5. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length}

Example:

Device(config)# ip nat pool VPN-18 10.10.0.0 10.10.255.255 netmask 255.255.0.0

Defines a pool of IP addresses for NAT.

Step 4

ip nat inside source list {{access-list-number | access-list-name} | route-map name} pool name [redundancy redundancy-id [mapping-id map-id | overload | reversible | vrf name]]

Example:

Device(config)# ip nat inside source list acl-18 pool VPN-18 redundancy 2 mapping-id 152
Enables NAT of the inside source address.

  • You must use a mapping ID to associate NAT with the redundancy group.

Step 5

end

Example:

Device(config)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Managing and Monitoring Stateful Interchassis Redundancy

All configuration commands in this task are optional. You can use the show commands in any order.

SUMMARY STEPS

  1. enable
  2. redundancy application reload group number [peer | self]
  3. show redundancy application group [group-id | all]
  4. show redundancy application transport {clients | group [group-id]}
  5. show redundancy application protocol {protocol-id | group [group-id]}
  6. show redundancy application faults group [group-id]
  7. show redundancy application if-mgr group [group-id]
  8. show redundancy application control-interface group [group-id]
  9. show redundancy application data-interface group [group-id]
  10. show monitor event-trace rg_infra all

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

redundancy application reload group number [peer | self]

Example:

Device# redundancy application reload group 2 self
Forces the active redundancy group (RG) to reload and the standby RG to become the active RG.

  • Use the redundancy application reload command to verify if the redundancy configuration is working. You must enter this command on the active RG.

Step 3

show redundancy application group [group-id | all]

Example:

Device# show redundancy application group 2

Displays summary information for the specified group or for all groups.

Step 4

show redundancy application transport {clients | group [group-id]}

Example:

Device# show redundancy application transport group 2

Displays transport information for the specified group or for all groups.

Step 5

show redundancy application protocol {protocol-id | group [group-id]}

Example:

Device# show redundancy application protocol 2

Displays protocol information for the specified group or for all groups.

Step 6

show redundancy application faults group [group-id]

Example:

Device# show redundancy application faults group 2

Displays information about faults for the specified group or for all groups.

Step 7

show redundancy application if-mgr group [group-id]

Example:

Device# show redundancy application if-mgr group 2

Displays information about the interface manager (if-mgr) for the specified group or for all groups.

Step 8

show redundancy application control-interface group [group-id]

Example:

Device# show redundancy application control-interface group IF-2

Displays interface information associated with redundancy groups for the specified control interface.

Step 9

show redundancy application data-interface group [group-id]

Example:

Device# show redundancy application data-interface group IF-2

Displays interface information associated with redundancy groups for the specified data interface.

Step 10

show monitor event-trace rg_infra all

Example:

Device# show monitor event-trace rg_infra all

Displays event trace information associated with all redundancy groups.

Configuration Examples for Stateful Interchassis Redundancy

Example: Configuring the Control Interface Protocol 

Device# configure terminal
Device(config)# redundancy
Device(config-red)# mode none
Device(config-red)# application redundancy
Device(config-red-app)# protocol 4
Device(config-red-app-prot)# name rg1
Device(config-red-app-prot)# timers hellotime 3 holdtime 10
Device(config-red-app-prot)# authentication text password
Device(config-red-app-prot)# bfd

Example: Configuring a Redundancy Group

Device# configure terminal
Device(config)# redundancy
Device(config-red)# application redundancy
Device(config-red-app)# group 1
Device(config-red-app-grp)# name rg1
Device(config-red-app-grp)# preempt
Device(config-red-app-grp)# priority 120 failover-threshold 80
Device(config-red-app-grp)# track 44 decrement 20
Device(config-red-app-grp)# timers delay 10 reload 20
Device(config-red-app-grp)# control GigabitEthernet0/1/0 protocol 1
Device(config-red-app-grp)# data GigabitEthernet0/1/2
Device(config-red-app-grp)# end
Device# configure terminal
Device(config)# interface GigabitEthernet 0/0/1
Device(config-if)# redundancy group 1 ip 10.10.1.1 exclusive decrement 20
Device(config-if)# redundancy rii 40

Example: Configuring a Redundant Traffic Interface

Device# configure terminal
Device(config)# interface GigabitEthernet 0/1/5
Device(config-if)# ip address 10.1.1.2 255.0.0.0
Device(config-if)# ip nat outside
Device(config-if)# ip virtual-reassembly
Device(config-if)# negotiation auto
Device(config-if)# redundancy rii 200
Device(config-if)# redundancy group 1 ip 10.1.1.200 exclusive decrement 10

Example: Configuring NAT with Stateful Interchassis Redundancy

Device# configure terminal
Device(config)# ip nat pool VPN-18 10.10.0.0 10.10.255.255 netmask 255.255.0.0
Device(config)# ip nat inside source list acl-18 pool VPN-18 redundancy 2 mapping-id 152

Additional References for Stateful Interchassis Redundancy

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Technical Assistance

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