Slashdot: Providers Ignoring DNS TTL?

Dean Anderson dean at av8.com
Sun May 1 05:01:47 UTC 2005


The questions of what various routers do now or did in the past is 
irrelevant. So, to wrap it up:

RFC 1546 give this rule about internetwork architecture on page 5:

   An internetwork has no obligation to deliver two successive packets
   sent to the same anycast address to the same host.

Whether it used to be impossible to utilize this rule, and whether anyone
actually presently uses this rule is irrelevant to the question of what
rules one needs to follow when building anycast systems.  RFC 1546 gives
some rules to follow, and they are violated at the peril of the
internetwork.

TCP "vixie-cast" violates this rule. It imposes the new rule that "an
internetwork MUST deliver to successive packets sent to the SAME anycast
address to the SAME host."  And no one has thought much about the
implications of that rule, (other than the original architects of RFC
1546).  Sure, it sort of happens most of the time with current routers and
current configurations, but load balancing over diverse paths isn't
limited to being slow and per-flow.  There are no IETF rules that require
that behavior. Implementors of networks and routers are free to use the
RFC 1546 design rule.

Assurances that typically, it happens that no one can "deliver two
successive packets sent to same anyast IP address to different hosts" is
no defense for TCP "vixie-cast" having violated the design principles
given for anycast in RFC 1546.

It is also objectionable to calling something "TCP anycast" that isn't TCP
anycast according to RFC 1546.

		--Dean

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