After reading the book: "OSPF_and_IS-IS_Choosing_an_IGP_for_Large-Scale_Networks" I understood very well why with ISIS the fragmentation is a bit harder.
Expanation: In OSPF we have few LSA packets (LSA1,2,3,4,5) and there are LSA packets with lower size than others...but in the case of ISIS we only have a LSP packets to send update one for level1 and another for Level2; that's why they needs to contain much more informatin and the size is higher than for example LSA3 in the case of OSPF.
Additionall the LSP is not an IP packet, it cannot take advantage of IP’s fragmentation mechanism. Therefore, IS-IS must have its own fragmentation mechanism called padding TLV."
With that said I would like to know if is required to enable padding TLV or if is enabled by default. At the same time some articles say that is not recommended to enable in large networks because adds overhead.
Do you know which commands could I use to verify if is enabled and which type of TLV padding (loos, strict...) is enabled?
I didn't found any traceoption command to debug "padding TLV"