hostname valid characters

[Bill McNAMARA_1]

Hi all,

another quick one..

Is an underscore a valid char in a hostname.

(too tired to make a test)
Later,
Bill

[Clemens van Everdingen]

Hi,

Yes this will be possible, but I believe not as first character.

If you use set_parms, this will check if the hostname is valid.
There is a checking mechnism in set_parms.

C.

[melvyn burnard]

To my knowledge, yes it is a valid character.
I KNOW I have seen a document about this, but do you think I can remember where? Not a chance.

[Bill McNAMARA_1]

I need certainty guys!
I guess I should check out some RFC..

Later,
Bill

[Clemens van Everdingen · Accepted solution]

Hi,

Found this info:

As mentionned in the RFC1033 : DOMAIN ADMINISTRATORS OPERATIONS GUIDE

The domain system allows a label to contain any 8-bit character.
Although the domain system has no restrictions, other protocols such as SMTP do have name restrictions. Because of other protocol restrictions, only the following characters are recommended for use in a host name (besides the dot separator):

"A-Z", "a-z", "0-9", dash and underscore

The underscore is now accepted as character in a hostname.

C.

[John Palmer]

It's valid as far as the system is concerned but following the letter of the RPC, it's NOT a valid character as far as DNS is concerned.

If you are using DNS then you have to specifically allow the underscore.

Personally, I'd avoid using it.

Regards,
John

[John Palmer]

From Support documentt ID A5650126...

The problem is that you have used an underscore character (_) in
the DNS server hostname. Starting with BIND 4.9.6, hostnames cannot
contain this character.

Solve the problem by changing the hostname and rebuilding the DNS server.

Also, in order to resolve other hostnames that have an "_" in them, add the following three lines to the very beginning of the named.boot file:

check-names primary ignore
check-names secondary ignore
check-names response ignore
end quote

Regards,
John

[Clemens van Everdingen]

Hi,

To allow for this, modify the "check-names" options lists in the named.conf file that hosts_to_named generates.

C.

[Bill McNAMARA_1]

Hey John,

how do I specify in DNS that the _ is good..

Later,
Bill

[Bill McNAMARA_1]

I am having a problem with DNS btw!

Later,
Bill

[melvyn burnard]

Bill, the set_parms hostname utility does some checking for unsupported vs supported characters.
Take a look at /sbin/set_parms/05_hostname and around line 772 you will get to the hostname check portion, and a listed supported character is definitely the underscore.
HTH

[Bill McNAMARA_1]

had a problem using the search today..
but eventually found this link:
explaining the issue also.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x52b6c8ecad09d6118ff40090279cd0f9,00.html

Thanks all,
Later,
Bill

[rick jones]

Even if/though an HP supplied or even other version of DNS serving software can be told to allow udnerscores in names...

...don't go there...

all it takes is one other bit of resolver or server code not within your control to make using an underscore in a hostname a cause for lack of connectivity.

It should be considered only an accident that earlier versions of DNS software allowed the underscore at all.