Re: [babel] WG Last Call for draft-ietf-babel-source-specific (2018-03-26 to 2018-04-09)

[Denis Ovsienko <[e-mail]>]

 ---- On Sat, 02 Jun 2018 09:05:01 +0100 Matthieu Boutier <[e-mail]> wrote ---- 
 > Thanks for your reading Denis, 
 >  
 > > (Here it could be helpful to provide a reference that helps the reader get the difference right.) 
 >  
 > Done. 
 >  
 > >   However, this extension is encoded using mandatory sub-TLVs, 
 > >   introduced in [BABEL], and therefore is not compatible with the older 
 > >   version of the Babel Routing Protocol [RFC6126].  Consequently, this 
 > >   extension MUST NOT be used with routers implementing RFC 6126, 
 > >   otherwise persistent routing loops may occur. 
 > >  
 > > (It looks like the right moment to stop for a moment and think. Could anybody briefly remind why leaving the protocol version 2 in 6126-bis is considered better than bumping it up to 3?) 
 >  
 > You're right, I will add some explicit statement saying that "6126 does 
 > not support mandatory sub-TLVs". 

Please correct me if the following interpretation is wrong. There is a deployed fleet of RFC 6126 devices and it is not going to disappear immediately. There is going to be a deployed fleet of SS-extended devices. When the two kinds randomly meet in the wild and source-specific routes start to propagate, the network can randomly break or degrade.

Acknowledging the problem in a document is a good start. But ending up with a design that fails to fail safe looks wrong. If the specification does not provide an implementer with some means to detect this situation and deal with it (as trivial as a protocol version number if nothing else works), the problem will end up dumped at the end user, which is not what they reasonably expect. Do you see what I mean?

[...]

 > > -<list style="hanging" hangIndent="10"> 
 > > +<list style="hanging" hangIndent="15"> 
 >  
 > I think it's fine with 10, as the base protocol uses this for all its lists. 

The formatting issue the above change fixes is difficult to see in XML. It is much easier to see in the .txt output.

-- 
    Denis Ovsienko