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

[Dhamija Amit]

Hi Adam
 
Thanks for first one how do you counted the header size as 27 bytes??
 
I have a doubt on second one that IOS-XR does padding even it has hello padding disable , atleast this is something 
which i can't see in ethereal.

Thanks
Amit Dhamija




________________________________
From: Adam Vitkovsky <adam.vitkovsky at swan.sk>
To: 'Dhamija Amit' <amiitdhamija at yahoo.com>; cisco-nsp at puck.nether.net 
Sent: Friday, November 22, 2013 6:37 PM
Subject: RE: [c-nsp] ISIS LSP-MTU and CLNS-MTU


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