Editing IS-IS (section)

== Wide metrics ==
When IS-IS was initially introduced, TLVs for '''IS reachability (TLV 2)''' and '''IP reachability (TLVs 128 and 130)''' could have interface metric no more than '''63''' (6 bits) and total accumulated path metric of no more than '''1023''' (10 bits).

Obviously, nowadays with higher link speeds and more hops in the path it would be challenging to stay within these limits.

Therefore, 2 new TLVs - '''TLV 22''' for '''Extended IS reachability''' and '''TLV 135''' for '''Extended IP reachability''' - were introduced. With this, now link metric can be up to 16.7 million (24 bits) and total accumulated path metric can be up to 4 billion (32 bits).

'''Older''' '''style metric''' is therefore called '''narrow metrics''', while '''new style metric''' - '''wide metrics'''. 

Wide metrics or narrow metrics can be set on level base.