Slashdot: Providers Ignoring DNS TTL?

Wed Apr 20 18:20:23 UTC 2005

On Apr 20, 2005, at 2:13 PM, Dean Anderson wrote:

> No, you are thinking of the (wrong) claims originally made by ISC  
> about
> how anycast would affect TCP to an anycast authoritative server.  ISC
> wrongly asserted that since BGP routes don't churn very fast  
> compared with
> DNS TCP connection lifetimes, that there should be no problem with  
> anycast
> and TCP.  This view has been shown to be wrong in the face of Per  
> Packet
> Load Balancing (PPLB) which has been demonstrated to work on BGP  
> links by
> haesu at towardex.com. Further, I showed that if you have PPLB on  
> interior
> (eg OSPF) links leading to different BGP peers, the problem also  
> happens.
> Packets are sent on a per packet basis to different places.

And I can show that if you give a pig wings....

Look, it breaks in certain situations.  But anycast implementations  
of TCP apps have worked "well" for a decade now.  Deal with the fact  
that not only do people use it, but users don't notice it.

Or don't.  No one here cares if you do.  Reality trumps lab tests.

> But caching servers are usually setup to load balance. Usually, the
> servers with the same IP address share an ethernet along with multiple
> routers.  So the packets are switched on essentially a per-packet  
> basis.
> Or possibly a per-arp basis that alters the MAC-based-forwarding  
> behavior
> of a switch.  This is fairly fine grained load balancing.

This is complete news to me.  Of course, I do not run most of the  
caching name servers on the Internet, so what do I know.  Do you?

Would anyone who runs an anycast recursive name server care to supply  
data points to support or refute Mr. Anderson's assertion?

Mr. Anderson, do you have any data points to support your assertion?

-- 
TTFn,
patrick