Cisco 6503 White Paper page 14

For these scenarios, SRM is now available.
Single Router Mode
SRM is provided as an option for customers who wish to implement redundant supervisor engines or MSFCs in a system with
only one active router in a chassis. SRM has the ability to use the Layer 2 and Layer 4 redundancy of Cisco Catalyst OS on
the supervisor engine as well as a streamlined approach to Layer 3 redundancy. The minimum software requirements are Cisco
Catalyst OS 6.3.1 and Cisco IOS Software Release 12.1(8)E2 for the MSFC.
SRM improves upon DRM. Specifically, SRM provides the following:
• A reduction in Layer 3 complexities for IP addressing and routing protocol neighbor relationships.
• A fix for the non-RPF traffic issue with having two active multicast routers on the same segment (because there is only
one active router in the chassis with SRM).
• A simpler configuration for the user as only a single command set is entered from one CLI and it applies to the active
router. This eliminates the challenge of ensuring that both MSFCs have the same configurations.
The following commands enable SRM:
MSFC-Sup-15 (config)# redundancy
MSFC-Sup-15 (config-r)# high-availability
MSFC-Sup-15 (config-r-ha)# single-router-mode
SRM Operation
In this mode, only the designated router will be visible to the network at any given time. The nondesignated router will be
started and will maintain exactly the same configuration as the designated router (the configurations are automatically
synchronized when SRM is active). However, the nondesignated router's interfaces will be kept in a line-down state and not
visible to the network. Routing protocol processes are also created on the nondesignated router, but they do not send or receive
updates from the network because all the interfaces are down. This is verified from the Cisco Catalyst OS command line
below. Note that both the supervisor engine and the MSFC in slot 2 are listed as standby.
SRM> (enable) show module
Mod Slot Ports Module-Type
--- ---- ----- ------------------------- ------------------- --- --------
1 1 2 1000BaseX Supervisor
15 1 1 Multilayer Switch Feature WS-F6K-MSFC2
2 2 2 1000BaseX Supervisor
16 2 1 Multilayer Switch Feature WS-F6K-MSFC2
If the designated router fails in an SRM configuration, the other MSFC changes state from nondesignated router to designated
router. This new designated router changes its interface state to link up and begins to build its routing table. It follows that the
control plane failover time will be proportional to the routing protocol configuration and complexity. However, there do exist
Layer 3 forwarding entries in the PFCx, which are used to forward routed traffic in the hardware path. The high availability
functions of the Catalyst OS are used to maintain this forwarding information after a failover. This allows for minimal impact
to the Layer 3 data plane traffic while the Layer 3 control plane converges. After the MSFC builds its routing table, the entries
in the PFCx can be updated.
Beginning in Cisco Catalyst OS version 12.1(11b)E, there is a transition timer feature for running SRM on the supervisor
2
engine 2/PFC . This timer configures the time that the new designated router will wait before downloading any new hardware
Cisco Express Forwarding entries to the PFC2. Due to differences in routing convergence times, the default of 120 seconds
might not be long enough to allow for complete convergence before programming the PFC2 hardware.
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Model
WS-X6K-SUP2-2GE
WS-X6K-SUP2-2GE
Cisco Systems, Inc.
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Sub Status
yes ok
no ok
yes standby
no standby