Subject: Re: [PATCH net-next 2/3] rds: Enable RDS IPv6 support

From: Sowmini Varadhan <[email-masked]>
Date: Tue, 26 Jun 2018 09:08:44 -0400

On (06/26/18 21:02), Ka-Cheong Poon wrote:
> 
> In this case, RFC 6724 prefers link local address as source.

the keyword is "prefers". 

> While using non-link local address (say ULA) is not forbidden,
> doing this can easily cause inter-operability issues (does the
> app really know that the non-link local source and the link
> local destination addresses are really on the same link?).  I
> think it is prudent to disallow this in RDS unless there is a
> very clear and important reason to do so. 

I remember the issues that triggered 6724. The "interop" issue
is that when you send from Link-local to global, and need forwarding,
it may not work.

but I dont think an RDS application today expects to deal with
the case that "oh I got back and error when I tried to send to
address X on rds socket rs1, let me go and check what I am bound
to, and maybe create another socket, and bind it to link-local"

You're not doing this for IPv4 and RDS today (you dont have to do this
for UDP, afaik)

This is especially true if "X" is a hostname that got resovled using DNS

> BTW, if it is really > needed, it can be added in future.

shrug. You are introducing a new error return.

--Sowmini