Re: Aliased names.

[GERMA Denis]

Hi,

You seem to be using gethostbyname in Version 1.6.3 to try to get the aliases 
in the GetNameInfo
function
which declare the classes for hostname, system, .....

I tested the gethostbyname (on Linux), and I confirme that the h_aliases only 
contains Info
when you call the gethostbyname with an aliased name. (The one we are looking 
for).

h_named  then contains the canonical name and h_aliases  contains the alias 
fully qualified name.

The solutions to add the aliased names in class, seems to be either  call the 
gethostbyname (and
or a cache)
each time there is a miss in the class search (Ronan KERYELL proposal),
or try to list the domain.

The solution may then be (I did not yet traducted in C.) :

echo 'lserver autoritative_dns_server
ls -a domain_name' | nslookup | grep hostname

This in fact produce the CNAME table.
and then grep the hostname in it.

Draw backs are then :
    It does not seems to work on non autoritative dns server (Not a general 
method). (Consider
Ronan KERYELL explanation)
    It implicitely list all machines (network traffic)
    It may be difficult to get the name for the autoritative DNS server in a 
complex DNS
hierarchie.
    The autoritative DNS server  may forbid listing the domain.

For the Ronan KERYELL proposal, draw backs may be :
    It does not fit with the actual architecture.
    A DNS query is issued each time a miss is issued and has not allready been 
seen.
    A cache containing  "class miss" may have to be maintained and is memory 
consuming.

Thanks for all.
D.Germa

Ronan KERYELL a écrit :

> >>>>> On Thu, 12 Apr 2001 16:33:35 +0200 (MET DST), address@hidden said:
>
>     >>  It sounds to me that what we are interested in is a map "name or
>     >> IP -> aliases" but the DNS CNAME tables are "aliases -> name" map.
>     >>
>     >> The only way I can figure out is to test the DNS for every new
>     >> cfengine class is met to see if we can find out one of our IP
>     >> adresses again.
>     >>
>     >> That would also solve the multiple name -> same IP case by the
>     >> way...
>     >>
>
>     Mark> It is supposedly possible to extract all names and aliases for
>     Mark> an IP address from the C structures, but when I tried it did not
>     Mark> work as expected.
>
> Sure, if they are in the C structures...
>
> I've not been clear enough :
>
> DNS CNAME, A or MX RR represent a mathematical function "name -> real name
> or IP"
>
> DNS PTR represent a mathematical function "IP -> name"
>
> It is what you get in the C structures, but *for a given* left element.
>
> But when cfengine is lauched, as for any command, you know the IP adresses of 
> the machine and
> also the hostname or nodename. Unfortunately you cannot know all the names
> that would target the same IPs because you cannot invert the DNS CNAME or
> A function and because the DNS PTR database give you only the main
> name... :-(
>
> So, what I propose is a lazy solution with a cache system : every time you
> encounter a new class, just do a DNS CNAME + A with recursion enabled to
> test whether it is an other name for the machine. If yes, put the class as
> true in the cache. Well, I guess that during the cfengine run the DNS
> table will not change... :-)
>
> It is the reason of the sendmail.cw file for example that states all the
> names the names sendmail is responsible for because she cannot figure it 
> out...
>
> --
>     Ronan KERYELL              |\/
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