Pre-Upgrade Instructions for IS-IS Metric Type

The command used to redistribute routes into IS-IS supports a parameter called metric-type, which can take one of two values: internal or external. In releases that do not support the external metric type, the routes are always advertised into IS-IS as internal, irrespective of whether you configure the metric-type to internal or external. The saved configuration itself correctly shows the value that you selected.

If the configuration file has redistribution commands that set the metric-type to external, after you upgrade to a release that supports the external metric type, the routes will be advertised into IS-IS as external routes. This constitutes a change in how the routes are advertised into IS-IS after the upgrade as compared to before the upgrade. This configuration can cause unintended traffic issues if the other switches in the network are not yet upgraded to a release that recognizes external routes in IS-IS.

To know which release supports the external metric type on your platform, see VOSS Release Notes for interoperability considerations.

To avoid unintentionally impacting traffic immediately following an upgrade, as a best practice, check the existing IS-IS redistribution configuration of a switch to determine if the metric-type is set to external in the redistribution commands. If metric-type external is not used in the redistribution, the switch can be upgraded using the normal upgrade procedures. If the metric-type external is used with any redistribution command, change it to internal, and then save the configuration. After this the switch can be upgraded using the normal upgrade procedures.

Commands to Check metric-type in Redistribution Configuration:

Switch:1(config-isis)#show ip isis redistribute [vrf WORD<1-16>]
================================================================================
  ISIS Redistribute List - GlobalRouter
================================================================================
SOURCE MET MTYPE      SUBNET   ENABLE LEVEL  RPOLICY
--------------------------------------------------------------------------------
RIP    0   internal   allow    TRUE   l1
OSPF   0   external   allow    TRUE   l1
LOC    0   external   allow    TRUE   l1

Commands to Change metric-type to Internal for GRT:

router isis
isis redistribute <protocol> metric-type internal
save config

The protocol can be one of the following: direct, ospf, static, rip or bgp.

Commands to Change metric-type to Internal for VRF:

router vrf WORD<1-16>
isis redistribute <protocol> metric-type internal
save config

The protocol can be one of the following: direct, ospf, static, rip or bgp.