Mirror Sites and CNAME

[Barry Margolin]

In article <3906A0FF.6EF42688 at uswest.net>,
Steve Cordova  <scordova at uswest.net> wrote:
>
>
>Barry Margolin wrote:
>
>> In article <Pine.BSF.3.96.1000420122335.16533A-100000 at ravi.lums.edu.pk>,
>> Saqib Mustafa  <01020103 at ravi.lums.edu.pk> wrote:
>> >
>> >I am having a problem assigning one canonical name to multiple mirror
>> >sites. I can assign IPs to the mirror site through the IN A entry but when
>> >I try to assign the CNAME to multiple sites and then I run named I get an
>> >error.
>>
>> You can't have multiple CNAME records for the same name.
>
>Can't you set Multiple-Cnames allow? or something like that? We had to do
>that for
>a major customer.

Yes.  I deliberately chose note to mention that, since I don't want to
encourage people to do things that violate the DNS specification.

For mirror sites, you probably don't want to do this, anyway.  The purpose
of mirror sites is usually to allow users to select the one that's closest
to them, but multiple-cnames won't do that -- it will just return one of
them randomly.  Another common use of mirrors is for fault tolerance -- if
one mirror is down, the user can select another one.  But BIND will only
return a single CNAME record in the response, so the client will never see
the others (if he queries again, he'll just get the same CNAME record from
his local server's cache, unless the TTL is set very low).

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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