IS-IS Single-Topology Support for IPv6



I have a question, which I am hoping someone can help clarify.

When running ISIS in ST for IPv6,  "wide metrics" are not required.  Thats is my understand,  thats how I tested, as well,  confirmed in the document output below.   

However that documentation continues on to say,   that IPv6 reachability is advertises using extended metrics?     This is where I am confused...how can that be if they are not enabled?

 

IS-IS Single-Topology Support for IPv6


When single-topology support for IPv6 is being used, either old- or new-style TLVs may be used. However, the TLVs used to advertise reachability to IPv6 prefixes use extended metrics. Cisco routers do not allow an interface metric to be set to a value greater than 63 if the configuration is not set to support only new-style TLVs for IPv4. In single-topology IPv6 mode, the configured metric is always the same for both IPv4 and IPv6.

IS-IS Multitopology Support for IPv6


When multitopology support for IPv6 is used, use the metric-style wide command to configure IS-IS to use new-style TLVs because TLVs used to advertise IPv6 information in link-state packets (LSPs) are defined to use only extended metrics.

Comments

  • Hi 1000BaseT,

    Is confusing to me too. Unfortunately that same statement is copied as-is in multiple document (even an IPv6 book).

    The way I understood it: you can use either old or new style TLV in ST. But if you choose either to use metric greater than 63 or use TLV 236 (for IPv6 prefix reach ability ), new-style (wide metric ) must be considered. Assumption is TLV 129 is good enough to just carry IPv6 as payload. 

    Hope someone corrects me if my understanding is wrong:)

    Sincerely,
    TF

    Sent from my iPhone

    On Mar 5, 2015, at 12:19 PM, 1000BaseT <[email protected]> wrote:



    I have a question, which I am hoping someone can help clarify.

    When running ISIS in ST for IPv6,  "wide metrics" are not required.  Thats is my understand,  thats how I tested, as well,  confirmed in the document output below.   

    However that documentation continues on to say,   that IPv6 reachability is advertises using extended metrics?     This is where I am confused...how can that be if they are not enabled?

     

    IS-IS Single-Topology Support for IPv6


    When single-topology support for IPv6 is being used, either old- or new-style TLVs may be used. However, the TLVs used to advertise reachability to IPv6 prefixes use extended metrics. Cisco routers do not allow an interface metric to be set to a value greater than 63 if the configuration is not set to support only new-style TLVs for IPv4. In single-topology IPv6 mode, the configured metric is always the same for both IPv4 and IPv6.

    IS-IS Multitopology Support for IPv6


    When multitopology support for IPv6 is used, use the metric-style wide command to configure IS-IS to use new-style TLVs because TLVs used to advertise IPv6 information in link-state packets (LSPs) are defined to use only extended metrics.




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