[c-nsp] ISIS LSP-MTU and CLNS-MTU

[Adam Vitkovsky]

Hi Amit,

Regarding LSP MTU:
(I'd assume the default size is below 1500 so 1492 seems right). 
My notes from an old book: 
max LSP size = 1492 bytes - header = 27 bytes == 1465 bytes for TLVs. 
LSP ID contains 8bit fragment id = max 256 fragments. 
=> 256*1465 to pack ip reachability. 
-assuming the first fragment will carry some other TLVs. 
==>aprox 31,000 prefixes. 

My findings regarding CLSN MTU:
In case the hello padding is disabled ISIS still sends IIH padded to the
full interface MTU -3B until the adjacency is formed. 
XR 4.2.3 will form ISIS adjacency with a remote system if incoming IIH is
max 5bytes larger than the interface CLNS MTU over which the IIH was
received. 


adam