Short Question :

Since DNS is anycast, is there any way for a DNS Server to know the "first" source DNS Query originated from?

Long Question : I've developed a custom DynDNS server using PowerDNS, I want to feed it information via web interface by users. I want the web interface to update records for each user "based on IP".

So when the D开发者_如何学PythonNS Server gets requests, If it could determine the source IP, it'd be easy to return records associated with that IP.

As long as I tested, the DNS Server can only know the "last" node IP on the DNS chain, not the source. Is there any way?

Regards

Google and Yahoo! submitted a draft (draft-vandergaast-edns-client-ip-01) to the IETF DNS Extensions Working Group that proposed a new EDNS0 option within DNS requests that recursive servers could use to indicate their own client's IP address to the upstream authoritative server.

The intent was to theoretically optimise the use of Content Delivery Networks by ensuring that the web server addresses returned were based on the end user's IP address, rather than on the address of the end user's DNS server.

The idea was not well received and wasn't accepted by the working group because it intentionally broke the caching layer of the DNS, and the draft has subsequently expired.

UPDATE - a variation on this has subsequently been published as RFC 7871.

Perhaps you have control of the software performing the lookup? If so, you could include the IP address as part of the request, e.g.

23-34-45-56.www.example.com

to which your custom-written server replies

23-34-45-56.www.example.com 1800 CNAME www-europe.example.com

or

23-34-45-56.www.example.com  300     A 34.45.56.67

etc.

If the client is a web browser, complications arise due to NAT, HTTP proxies, and the inability to query host interface addresses directly from Javascript. However, you might be able to do an AJAX-style lookup to a what's-my-ip service, which understands X-Forwarded-For.

Long answer to Short Question :

DNS is not anycast. Some content DNS server owners use anycasting to distribute servers in multiple physical locations around the world, but the DNS/UDP and DNS/TCP protocols themselves are not anycast. The notion simply doesn't exist at that protocol layer.

Short answer to Long Question :

No.

Expansion

As noted, there's nothing in the DNS protocol for this. Moreover, the relationship between front-end and back-end transactions at a caching resolving proxy DNS server is not one-to-one.

You'll have to use whatever client differentiation mechanisms exist in the actual service protocol that you're using, instead of putting your client differentiation in the name→IP address lookup mechanism. Client differentiation for other services doesn't belong in name→IP address lookup, anyway. Such lookup is common to multiple protocols, for starters. Use the mechanisms of whatever actual service protocol is being used by the clients who are communicating with your servers.