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[RRG] transport relying on DNS



William Herrin wrote:

 DNS lookups will *block* most applications, until the DNS resolution
 succeeds or fails.

 And that has perception in user-space, but no impact to the underlying
 protocols.

 However, delays *within* the transport regime, are an entirely different
 can of worms.

 Unless the transport itself is modified to handle this, I think it's
 best to see if we can avoid this.
 I think it is a non-negligible issue.

If I correctly understand your criticism, it's that an ongoing
transport mustn't pause for an expired DNS TTL. I agree and this is
addressed in the TRRP document's section on ITRs.
Actually, while that is one concern, it isn't the primary or general concern.

The issue is, normally, DNS is used by an application, before initiating a connection.
And, not all connections that applications establish, involve DNS at all.

But, it is the application that knows DNS is being used.

If you start adding DNS into the transport itself, even remotely (e.g. at an ITR), it changes, however subtly, the expected behavior of the transport, especially on the first packet.

And, it also presupposes that DNS servers/resolvers for root, TLDs (especially arpa), and reachable destinations, will be available 100% of the time. While generally that is reasonable to expect, it is not universally so. (There have been instances where outages in some parts of the Internet, left large swaths of regions without root servers reachable, which was Very Bad.)

I will suggest, however, that making small changes to common transport protocols (TCP and UDP at least), to make them suitably aware and compatible with the DNS stuff going on, might allay the concerns.

However, that means host stack changes. Not necessarily a non-starter, but something that would need to be itemized in discussions of map-and-encap solutions that rely on DNS (such as TRRP).

Brian

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