isis route redistribution

fonque

When redistributing into ISIS, what is the difference between an isis metric type of internal and an isis metric type of exteral? I cannot seem to find any documentation to explain this.

is this the same as L1 or L2??

btowntech

"Routes may be redistributed into IS-IS with either internal or external metrics (internal is the default) and as either level 1 or leve 2 routes (level 2 is the default). The metric type determines the base metric value of the redistributed routes. The metric type of an internal metric type will be lower than 64. The metric value of an external metric will be between 64 and 128." (Routing TCP/IP Vol I, 2nd Ed, pg. 664)

Also here is a link to the redistribution of IS-IS on Cisco:

IS-IS IP Routing

Hope this helps!

fonque

thanks for the reply. So "external" just keeps redistributed routes from being able to compete with routes internal to the isis routing domain?

billscott92787

That's what I take out of it. The link provided: Intermediate System-to-Intermediate System Protocol [IP Routing] - Cisco Systems


Specifies


"Redistribution

The Integrated IS-IS specification describes the way routers are allowed to redistribute external prefixes. The Cisco implementation differs from the specification and allows more flexibility.

Redistribution from any other routing protocol, static configuration, or connected interfaces is allowed in any type of router (Level 1 and Level 2). By default the metric type will be set as internal, which means that the metric of the route will compete with all other internal routes. Metric type may be set to external. In that way the prefix will have a metric equal to the cost specified in the redistribution command plus a value of 64.5 Although the metric is increased if the metric is flagged as external on redistribution, the internal/external bit used to increase the metric is actually ignored when calculating routes unless the use of external metric is specified in the configuration.

It is recommended that the metric type internal always be used when redistributing. Wide-metric TLVs do not use and discriminate between internal and external. "



Which confirms that if the links are set to Internal the metric of the route will compete with all other internal routes, if set to external the metric is used which is specified in the redistribution plus 64.5. The last portion "the internal/external bit used to increase the metric is actually ignored when calculating routes unless the use of external metric is specified in the configuration."

What I get out of that is that unless it is set to external then the 64.5 is ignored when calculating routes.