Cisco Systems 6503 manual Single Router Mode, SRM Operation

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		Model	Sub	Status
---	----	----- -------------------------		-------------------	---	--------
1	1	2	1000BaseX Supervisor	WS-X6K-SUP2-2GE	yes	ok
15	1	1	Multilayer Switch Feature	WS-F6K-MSFC2	no	ok
2	2	2	1000BaseX Supervisor	WS-X6K-SUP2-2GE	yes	standby
16	2	1	Multilayer Switch Feature	WS-F6K-MSFC2	no	standby

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 engine 2/PFC2. 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.

Cisco Systems, Inc.

All contents are Copyright © 1992–2002 Cisco Systems, Inc. All rights reserved. Important Notices and Privacy Statement.

Page 14 of 19