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Quick Mail Log Question - Linux / Unix Administration

Hi All, I, like everyone else, is getting this error message: Unable to get canonical name of client 192.168.1.100: Unknown host Question is, I have no idea on how to fix it. Everyone says it has something to do with DNS, or Reverse DNS. Is that something I fix on my own server, or my ISP fixes on theirs? If I am to fix it on my server, how do I do that? I have no clue. Any help would be appreciated....... Thanks a bunch. Arthur...

  1. #1

    Default Quick Mail Log Question


    Hi All,

    I, like everyone else, is getting this error message:

    Unable to get canonical name of client 192.168.1.100: Unknown host

    Question is, I have no idea on how to fix it. Everyone says it has
    something to do with DNS, or Reverse DNS. Is that something I fix on
    my own server, or my ISP fixes on theirs?

    If I am to fix it on my server, how do I do that? I have no clue. Any
    help would be appreciated.......

    Thanks a bunch.

    Arthur

    amerar@iwc.net Guest

  2. #2

    Default Re: Quick Mail Log Question

    On 6 Sep 2005 07:45:14 -0700, net
    <net> wrote: 
    I haven't seen it. Who do you mean by "everyone else"?
     
    Is the address 192.168.1.100 listed in /etc/hosts? Do you have a DNS
    server on your LAN?

    --
    Atlanta makes it against the law to tie a giraffe to a telephone pole
    or street lamp.
    Bill Guest

  3. #3

    Default Re: Quick Mail Log Question

    > Unable to get canonical name of client 192.168.1.100: Unknown host
     

    Depends on how you wish to solve this, and a lot also depends on the MTA
    you're using. But fist lets see what this error means:

    A 'canonical name' is another description of the full name of the host.
    A host is usually described by a hostname + domainname (for example;
    mail.google.com where 'mail' is the hostname, etc.). Another way to
    describe this is the FQDN (Fully Qualified Domain Name).

    Normally you lookup the IP number which belongs to a hostname/FQDN. This
    can be done in a number of ways... The easiest way is to add this the IP
    and the name to /etc/hosts. Another option is to use or setup a DNS
    server. So summing up: you're basicly "linking" a name with an IP
    adress.

    However, it is also possible to do this the other way around. In other
    words; "link" an IP adress with a name. Whenever you lookup the IP
    adress you'll get the associated name. As you already mentioned yourself
    its also called a 'reverse lookup'. Its called that way because "normal"
    ('forward') lookups are done by checking up on a name.


    Now how to get rid of the message.. Most MTA's will try to lookup the
    name of a host, in many cases MTA's are setup to only accept mail from
    hosts which have a reverse name attached to them. The easiest way for
    you to get rid of this is by telling your MTA not to do reverse lookups.

    Another, more difficult, option is to install your own DNS server and
    tell it that you'd like to 'associate' 192.168.1.100 with a name...


    The option to disable reverse lookups on your MTA should be doented.
    If you're considering to setup your own DNS server I'd like to point you
    to the DNS Howto (http://www.tldp.org/HOWTO/DNS-HOWTO.html) as well as
    the Bind9 doentation (http://www.isc.org/sw/bind/).


    --
    Groetjes, Peter

    ..\\ PGP/GPG key: http://www.catslair.org/pubkey.asc
    Lion-O Guest

  4. #4

    Default Re: Quick Mail Log Question


    Well, I run my own mailserver. That IP address, 192.168.1.100 is the
    IP of one of my internal machines. So, I'm not sure how it should be
    listed in /etc/hosts.

    I mean, it has no DNS and I'm not running my own DNS. So, I'm not sure
    how to solve this. Also, what does MTA stand for???

    Thanks,

    Arthur

    amerar@iwc.net Guest

  5. #5

    Default Re: Quick Mail Log Question

    In article <googlegroups.com>,
    net wrote:
     

    192.168.1.100 host100.yourdomain.com
     

    192.168.x.x addresses are private addresses, and they don't have any
    mapping in the public DNS. So you need to either run your own internal
    DNS server with these reverse entries, or add them to your /etc/hosts
    file as above.

    MTA stands for Mail Transfer Agent, the technical term for a mail server.

    --
    Barry Margolin, mit.edu
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
    Barry Guest

  6. #6

    Default Re: Quick Mail Log Question


    A typical /etc/hosts file looks like this:

    127.0.0.1 localhost.localdomain localhost
    192.168.1.160 some.domain.com some
    192.168.1.110 some2.domain.com some2

    But, 192.168.1.100 is a windows box, which has no domain name. So, how
    would I list in this the /etc/hosts file?

    Thanks,

    Arthur

    amerar@iwc.net Guest

  7. #7

    Default Re: Quick Mail Log Question

    net wrote: 

    All hosts with an IP number have a domain name if there
    is even one associated host that has a domain name.

    Get the hostname of the Windows box. Right click on
    My Computer, select Properties. The Computer Name
    tab will give the short name. It will not have any
    spaces because spaces are forbidden in hostnames,
    so if it is incorrectly named repair that damage.
    Then add the name of the domain and there you go.
    Register it in AD, NIS and/or DNS if you have any
    of those in addition to the hosts file.

    Doug Guest

  8. #8

    Default Re: Quick Mail Log Question


    Thanks, I'll try making that entry and see what happens. So, the
    domain name is basically just the name of the Windows box......let's
    see what happens.

    amerar@iwc.net Guest

  9. #9

    Default Re: Quick Mail Log Question


    Thanks, I'll try making that entry and see what happens. So, the
    domain name is basically just the name of the Windows box......let's
    see what happens.

    So, the /etc/hosts now looks like this:

    127.0.0.1 localhost.localdomain localhost
    192.168.1.160 some.domain.com some
    192.168.1.110 some2.domain.com some2
    192.168.1.100 windowsbox windowsbox

    amerar@iwc.net Guest

  10. #10

    Default Re: Quick Mail Log Question

    net wrote: 

    You missed the pattern.

    192.168.1.100 windowsbox.domain.com windowsbox

    Doug Guest

  11. #11

    Default Re: Quick Mail Log Question


    So, even though the windows box does not truely have a domain name I
    still need the line:windowsbox.domain.com?

    Well, since I have no idea, I'll trust you and make the
    change..........

    Thanks,

    Arthur

    amerar@iwc.net Guest

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