Section 8-5. MSFC Redundancy with Configuration Synchronization

8-5. MSFC Redundancy with Configuration Synchronization

• In config-sync mode, both MSFCs are active at all times; all interfaces and routing processes are available and active on both modules.

• One MSFC is "designated" and maintains the master copies of startup and running configurations. The other is "nondesignated" and receives its configurations from the designated module.

• The nondesignated MSFC can be monitored through an EXEC session, but doesn't allow the configuration mode.

• Config-sync mode allows an immediate failover because both MSFCs are always active. All VLAN interfaces are up, and any configured routing protocols are active on both modules.

• For MLS, either of two redundant MSFC modules can be involved in setting up a flow cache entry. The PFC is aware of both RP modules.

• For CEF, only the designated MSFC downloads the FIB and adjacency table information to the other modules. The designated MSFC is the one that initializes first, in the lowest module slot position.

• HSRP should be used to provide a redundant gateway address on each VLAN. Both MSFCs share a common gateway address, while operating their own unique interface addresses. (See section "8-6: Router Redundancy with HSRP" for more information about HSRP.)

• After config-sync mode has been enabled and is active, any configuration changes that are made on the designated MSFC are automatically synchronized with the nondesignated module:

  - Whenever you enter the write mem or copy source startup-config commands, the startup configuration is updated across MSFCs.

  - Whenever you enter the copy source running-config command, the running configuration is updated across MSFCs.

  - As you enter commands in configuration mode, they are also sent to and executed on the nondesignated MSFC.

Config-sync Redundancy Configuration

1.

Enable config-sync mode on the designated MSFC:

COS	N/A
IOS	(global) redundancy (redundancy) high-availability (highavailability) config-sync

The designated MSFC can be arbitrarily chosen and is the first module to be initialized with config-sync enabled. Generally, it is easier to start with the MSFC located in chassis slot 1 (session 15).

TIP

The config-sync mode will be administratively enabled at this point. However, config-sync mode requires that the designated MSFC have configuration information for both MSFCs because it keeps the master configuration. This requires some commands to have the alt keyword to specify parameters for the nondesignated MSFC.

The operational config-sync state will not become active until the alternate information is configured and the nondesignated MSFC has config-sync enabled.

2.

Configure any alternate parameters on the designated MSFC.

TIP

If you have already configured the designated MSFC for some features, you will have to enter some commands again to provide alternate values for the nondesignated MSFC. Remember that the designated MSFC keeps the master configuration for both MSFCs. The command syntax for some commands is changed to allow both the slot 1 MSFC (before the alt keyword) and the slot 2 MSFC (after the alt keyword) values to be given in the same command line.

If you begin with the slot 1 MSFC as the designated module, it will be intuitive that the command parameters are laid out as "designated alt nondesignated."

Notice that in most cases the whole command is repeated after the alt keywordnot just the command parameters.

a. (Optional) MSFC host name:

COS	N/A
IOS	(global) hostname hostname alt hostname hostname

b. (Optional) Default IP gateway:

COS	N/A
IOS	[View full width] (global) ip default-gateway ip-address alt ip default-gateway ip-address

c. (Optional) BGP router ID:

COS	N/A
IOS	(global) router bgp as-number (router-bgp) bgp router-id ip-address [alt ip-address]

d. (Optional) OSPF router ID:

COS	N/A
IOS	(global) router ospf process-id (router-ospf) router-id ip-address [alt ip-address]

e. (Optional) Interface IP address:

COS	N/A
IOS	[View full width] (interface) ip address ip-address mask [secondary] alt [no] ip address ip-address mask [secondary]

This command must be repeated for every interface. If the slot 2 MSFC doesn't have a corresponding active interface, use the no keyword.

TIP

Be careful when you are entering this command for secondary addresses. It is very easy to remember the secondary keyword on the designated portion but forget to type the secondary keyword for the alternate portion. If you forget the secondary keyword, the IP address you enter displaces any previously assigned primary address.

f. (Optional) HSRP group number and IP address:

COS	N/A
IOS	[View full width] (interface) standby [group] ip [ip-address [secondary]] alt [no] standby [group] ip [ip-address [secondary]]

Again, if you are using secondary addresses, make sure you enter the secondary keyword for both MSFC interfaces.

g. (Optional) HSRP priority and delay:

COS	N/A
IOS	[View full width] (interface) standby [group] priority priority [preempt [delay delay]] alt standby [group] priority priority [preempt [delay delay]]

The HSRP priorities (1 to 255, default 100) should be set to different values for the two MSFC interfaces. Choose a higher value for the interface that will become the active HSRP address.

h. (Optional) IPX network:

COS	N/A
IOS	[View full width] (interface) ipx network network [encapsulation encap-type [secondary]] alt ipx network network [encapsulation encap-type [secondary]]

3.

Save the configuration on the designated MSFC:

COS	N/A
IOS	(exec) copy running-config startup-config

4.

Enable config-sync mode on the nondesignated MSFC:

COS	N/A
IOS	(global) redundancy (redundancy) high-availability (highavailability) config-sync

Config-sync mode will not become operational until both MSFC modules have it configured and enabled. As soon as both modules have config-sync mode enabled, a 1-minute timer starts to allow the modules to stabilize and communicate. When this period ends, the designated MSFC copies its running configuration to the non-designated MSFC.

Displaying Information About Config-sync Redundancy

You can use the switch commands in Table 8-6 to display helpful information about config-sync redundancy.

Table 8-6. Commands to Display the Config-sync Redundancy Status

Display Function	Switch OS	Command
Config-sync status	COS	N/A
	IOS	(exec) show redundancy