Hello,
wrote: Hi Gongyayu
You will see the attached bit in the cases where either you are having ISIS connections inside of a routing-instance or a logical system.
It does not matter, ISIS adjacency in GRT behaves the same way.
wrote: If you have isis L1 only adjacency between to different nodes (no under routing instance or logical system) then you will not see the attached bit in the LSP.
Again, routing-instance/logical system or GRT does not matter. What matters is L2 IS (not L1!) being able to reach another L2 IS.
In plain English - ATT bit is seen in L1 LSP being sent by L1/L2 IS but it's L2 part of L1/L2 IS which needs to reach (i.e. calculate the SPF towards) another L2 IS.
ISO 10589 standard is quite authoritative in this regard, google for it.
HTH
Thx
Alex