[MUD-Dev] How to support 1000+ simultaneous connections, and some philosophy.

Mark Gritter mark at erdos.Stanford.EDU
Thu Mar 11 23:07:53 New Zealand Daylight Time 1999


J C Lawrence writes:
> 
> On Thu, 11 Mar 1999 22:28:16 -0700 
> Chris Gray<cg at ami-cg.GraySage.Edmonton.AB.CA> wrote:
> 
> > [Petri Virkkula:]
> 
> > Doesn't that require a custom DNS, so that it does hand out the IP's
> > in round-robin fashion? What about DNS's that cache associations?
> 
> Round-robin DNS ias part of the base BIND/named supports.  It comes by
> default -- all you have to do is define more than one IP per host.
> 

To expand that a little bit--- if the name is associated with multiple
addresses, all of them get reported, but the "first" one varies from
request to request, even on cached entries.  The resolver usually
takes the first IP address, but I'm not sure if this is required.

Caching is more of a problem if you want to do your own load-balancing.  
The recommended solution is usually to use short TTLs.

Interestingly, BIND also supports round-robin DNS based on aliases.
If you put multiple CNAME entries in the database, the one you get back
alternates between the aliases, e.g.,

server	cname	foo
	cname	bar
	cname	quux
foo	a	10.0.0.10    # first return this name
bar	a	10.0.0.11    # 2nd request gets this
quux	a	10.0.0.12

This isn't actually defined as meaningful in the relevant RFCs.  But I 
think it's nicer when you want to enforce a 1 canonical name <-> 1 address 
policy.

Mark Gritter
mgritter at cs.stanford.edu


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