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Shell Programming and Scripting
Check for valid hostnames
Post 302974674 by RavinderSingh13 on Thursday 2nd of June 2016 04:34:14 AM
06-02-2016
Moderator
Quote:
Hello,
I am trying to develop a script to check for valid hostnames. Below are the prerequisites for a valid hostname which I got from wiki :
Hostnames are composed of series of labels concatenated with dots, as are all domain names. For example, "en.wikipedia.org" is a hostname. Each label must be between 1 and 63 characters long, and the entire hostname (including the delimiting dots but not a trailing dot) has a maximum of 253 ASCII characters.
The Internet standards (Requests for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters 'a' through 'z' (in a case-insensitive manner), the digits '0' through '9', and the hyphen ('-'). The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits. No other symbols, punctuation characters, or white space are permitted.
Could someone please help.
Thanks
Rahul
I am trying to develop a script to check for valid hostnames. Below are the prerequisites for a valid hostname which I got from wiki :
Hostnames are composed of series of labels concatenated with dots, as are all domain names. For example, "en.wikipedia.org" is a hostname. Each label must be between 1 and 63 characters long, and the entire hostname (including the delimiting dots but not a trailing dot) has a maximum of 253 ASCII characters.
The Internet standards (Requests for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters 'a' through 'z' (in a case-insensitive manner), the digits '0' through '9', and the hyphen ('-'). The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits. No other symbols, punctuation characters, or white space are permitted.
Could someone please help.
Thanks
Rahul
Good to see you in forums
. Regarding above query I would like to say it completely depends on the organization like they are really following the mentioned rules/guidelines or not. Why not do a ping test for each host and find out(means--> if a host is valid it will pass the test), please do let me know your thoughts on same. Thanks,
R. Singh
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LEARN ABOUT FREEBSD
hostname
HOSTNAME(7) BSD Miscellaneous Information Manual HOSTNAME(7) NAME
hostname -- host name resolution description DESCRIPTION
Hostnames are domains, where a domain is a hierarchical, dot-separated list of subdomains; for example, the machine monet, in the Berkeley subdomain of the EDU subdomain of the Internet would be represented as monet.Berkeley.EDU (with no trailing dot). Hostnames are often used with network client and server programs, which must generally translate the name to an address for use. (This func- tion is generally performed by the library routine gethostbyname(3).) Hostnames are resolved by the Internet name resolver in the following fashion. If the name consists of a single component, i.e., contains no dot, and if the environment variable ``HOSTALIASES'' is set to the name of a file, that file is searched for any string matching the input hostname. The file should consist of lines made up of two white-space sepa- rated strings, the first of which is the hostname alias, and the second of which is the complete hostname to be substituted for that alias. If a case-insensitive match is found between the hostname to be resolved and the first field of a line in the file, the substituted name is looked up with no further processing. If the input name ends with a trailing dot, the trailing dot is removed, and the remaining name is looked up with no further processing. If the input name does not end with a trailing dot, it is looked up by searching through a list of domains until a match is found. The default search list includes first the local domain, then its parent domains with at least 2 name components (longest first). For example, in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berke- ley.EDU. Lithium.CChem.EDU will not be tried, as there is only one component remaining from the local domain. The search path can be changed from the default by a system-wide configuration file (see resolver(5)). SEE ALSO
gethostbyname(3), resolver(5), mailaddr(7) HISTORY
Hostname appeared in 4.2BSD. BSD
December 25, 2013 BSD