[Isis-wg] New WG document

[Tony Li]

Jeff,


|      Therefore, this RFC should be explicitly limited in application to
|      physical layers that have a minimum frame size of 1500 bytes or
|      less (excluding source & destination MAC addresses and Ethertype
|      fields).  


Thanks, yes.  FWIW, the primary driver behind this is Jumbo Frames on
Gigabit Ethernet.  The above caveat is reasonable in case someone ever
generalizes stuff.


|  3.  I am curious why IS-IS frames larger than 1500 would be desirable.


Jumbo Frames are going to get deployed to avoid MTU issues in the
backbone.  As IS-IS tends to use the available MTU, we need some
well-defined way of encapsulating PDUs.


|      The following are potential reasons why it would be better to
|      support large IS-IS PDUs (per the draft) than to have separate
|      MTU sizes for IS-IS and the data protocols (the alternative)
|  
|      A)  Checking consistency of MTU size settings between routers on
|          a LAN.
|  
|          I understand that IS-IS's ability to verify that frames of a
|          certain size can be exchanged on a link is useful, but it is
|          far more important for maintaining the integrity of route
|          exchange than data exchange, because of the nasty problems
|          that result from incomplete route propagation (far worse to
|          diagnose and repair than simple data loss).


Insuring that the data exchange happens is the key point.  MTU issues in
the data plane are no fun and IS-IS as it stands today obviates the issue.
We would like to preserve this property.


Tony