tag
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... AS number as a form of tagging to
identify interior as well as exterior routing processes. This tag
does not need to be unique unless routing information is indeed
...
... identifier for
tagging their IGP processes. However, this tag does not need to be
globally unique. In practice this information is never seen by
exterior routing protocols ...
... AS number as an IGP
tag; if you do not, choosing from the private use range is also
acceptable (see "Reserved AS Numbers ...