FAQ
Has anyone had problems accessing random websites since going up to 6.4?


Since about the day after I got partly upgraded, if I try to access
nytimes.com, or orbitz.com, I get server not found.


With a lot of work, I, my manager, and the other admin, found that setting
options edns0 in /etc/resolv.conf fixed it - I suspect that the network
folks updated their internal nameservers (which are M$) about that time...
but... we got this Thurs. Friday, I went to look, lunchtime, at a story,
and back to the same. Later, and I think I was playing around, it came
back.


Just now, over lunch, it failed... until I restarted nscd. My manager
tells me it's caching... but it seems to be caching momentary failures.


So: has anyone else seen oddness that might be related to nscd?


mark

Search Discussions

  • Mark Roth at Mar 25, 2013 at 6:06 pm

    m.roth at 5-cent.us wrote:
    Has anyone had problems accessing random websites since going up to 6.4?

    Since about the day after I got partly upgraded, if I try to access
    nytimes.com, or orbitz.com, I get server not found.

    With a lot of work, I, my manager, and the other admin, found that setting
    options edns0 in /etc/resolv.conf fixed it - I suspect that the network
    folks updated their internal nameservers (which are M$) about that time...
    but... we got this Thurs. Friday, I went to look, lunchtime, at a story,
    and back to the same. Later, and I think I was playing around, it came
    back.

    Just now, over lunch, it failed... until I restarted nscd. My manager
    tells me it's caching... but it seems to be caching momentary failures.

    So: has anyone else seen oddness that might be related to nscd?

    A quick followup of myself to provide more info: I see, in /etc/nscd.conf,
    that all the negative ttl's appear to be 20 sec, but I'm resonably sure
    that once I lose it, it's > 20 sec before go back to try again, and it's
    still not gone.


    mark
  • Cliff Pratt at Mar 25, 2013 at 9:32 pm

    On Tue, Mar 26, 2013 at 6:26 AM, wrote:
    Has anyone had problems accessing random websites since going up to 6.4?

    Since about the day after I got partly upgraded, if I try to access
    nytimes.com, or orbitz.com, I get server not found.

    With a lot of work, I, my manager, and the other admin, found that setting
    options edns0 in /etc/resolv.conf fixed it - I suspect that the network
    folks updated their internal nameservers (which are M$) about that time...
    but... we got this Thurs. Friday, I went to look, lunchtime, at a story,
    and back to the same. Later, and I think I was playing around, it came
    back.

    Just now, over lunch, it failed... until I restarted nscd. My manager
    tells me it's caching... but it seems to be caching momentary failures.

    So: has anyone else seen oddness that might be related to nscd?
    Do you want the whole book? 'nscd' is a synonym for weird. I've had
    many strange DNS issues which have been solved by either bouncing nscd
    or purging its cache entries.


    However, you appear to be using nscd on your machine to cache DNS and
    using the internal MS DSN servers to do the actual lookups. Am I
    correct? In which case, the MS DNS server should be caching the DNS
    lookups anyway, so you probably don't derive a lot of benefit from the
    nscd unless you do a lot of repeated DNS lookups.


    Cheers,


    Cliff
  • Gary Greene at Mar 25, 2013 at 11:06 pm

    On Tuesday, Cliff Pratt wrote:
    On Tue, Mar 26, 2013 at 6:26 AM, wrote:
    Has anyone had problems accessing random websites since going up to 6.4?

    Since about the day after I got partly upgraded, if I try to access
    nytimes.com, or orbitz.com, I get server not found.

    With a lot of work, I, my manager, and the other admin, found that setting
    options edns0 in /etc/resolv.conf fixed it - I suspect that the network
    folks updated their internal nameservers (which are M$) about that time...
    but... we got this Thurs. Friday, I went to look, lunchtime, at a story,
    and back to the same. Later, and I think I was playing around, it came
    back.

    Just now, over lunch, it failed... until I restarted nscd. My manager
    tells me it's caching... but it seems to be caching momentary failures.

    So: has anyone else seen oddness that might be related to nscd?
    Do you want the whole book? 'nscd' is a synonym for weird. I've had
    many strange DNS issues which have been solved by either bouncing nscd
    or purging its cache entries.

    However, you appear to be using nscd on your machine to cache DNS and
    using the internal MS DSN servers to do the actual lookups. Am I
    correct? In which case, the MS DNS server should be caching the DNS
    lookups anyway, so you probably don't derive a lot of benefit from the
    nscd unless you do a lot of repeated DNS lookups.

    Cheers,

    Cliff

    NSCD is also necessary if you're running an LDAP or NIS environment, so don't just turn it off if you're using external authentication services. In a Winbind environment, NSCD is unnecessary however.


    --
    Gary L. Greene, Jr.
    Sr. Systems Administrator
    IT Operations
    Minerva Networks, Inc.
  • Stephen Harris at Mar 25, 2013 at 11:20 pm

    On Mon, Mar 25, 2013 at 11:06:31PM +0000, Gary Greene wrote:
    NSCD is also necessary if you're running an LDAP or NIS environment,

    Not necessary in a NIS environment on a LAN 'cos NIS is UDP based and
    very very fast to respond. LDAP, however, pretty much needs nscd (or
    sssd) in order to be halfway near performant.


    --


    rgds
    Stephen
  • Gordon Messmer at Mar 25, 2013 at 11:29 pm

    On 03/25/2013 04:06 PM, Gary Greene wrote:
    NSCD is also necessary if you're running an LDAP or NIS environment,
    so don't just turn it off if you're using external authentication
    services. In a Winbind environment, NSCD is unnecessary however.

    I would advise all users to migrate to sssd from nscd.
  • Cliff Pratt at Mar 26, 2013 at 2:14 am

    On Tue, Mar 26, 2013 at 12:06 PM, Gary Greene wrote:
    On Tuesday, Cliff Pratt wrote:
    On Tue, Mar 26, 2013 at 6:26 AM, wrote:
    Has anyone had problems accessing random websites since going up to 6.4?

    Since about the day after I got partly upgraded, if I try to access
    nytimes.com, or orbitz.com, I get server not found.

    With a lot of work, I, my manager, and the other admin, found that setting
    options edns0 in /etc/resolv.conf fixed it - I suspect that the network
    folks updated their internal nameservers (which are M$) about that time...
    but... we got this Thurs. Friday, I went to look, lunchtime, at a story,
    and back to the same. Later, and I think I was playing around, it came
    back.

    Just now, over lunch, it failed... until I restarted nscd. My manager
    tells me it's caching... but it seems to be caching momentary failures.

    So: has anyone else seen oddness that might be related to nscd?
    Do you want the whole book? 'nscd' is a synonym for weird. I've had
    many strange DNS issues which have been solved by either bouncing nscd
    or purging its cache entries.

    However, you appear to be using nscd on your machine to cache DNS and
    using the internal MS DSN servers to do the actual lookups. Am I
    correct? In which case, the MS DNS server should be caching the DNS
    lookups anyway, so you probably don't derive a lot of benefit from the
    nscd unless you do a lot of repeated DNS lookups.

    Cheers,

    Cliff
    NSCD is also necessary if you're running an LDAP or NIS environment,
    so don't just turn it off if you're using external authentication services. In
    a Winbind environment, NSCD is unnecessary however.
    Ah, yes, indeed. Thanks Gary,


    Cliff
  • Gordon Messmer at Mar 25, 2013 at 11:43 pm

    On 03/25/2013 10:26 AM, m.roth at 5-cent.us wrote:
    Just now, over lunch, it failed... until I restarted nscd. My manager
    tells me it's caching... but it seems to be caching momentary failures.

    That could be coincidence. As far as I know, Firefox will not use nscd
    for hostname lookups. I confirmed Firefox using strace, but not others.


    If edns0 changed your system's behavior, I would suspect that someone
    recently turned on DNSSEC, and it's not working correctly.

Related Discussions

Discussion Navigation
viewthread | post
Discussion Overview
groupcentos @
categoriescentos
postedMar 25, '13 at 5:26p
activeMar 26, '13 at 2:14a
posts8
users5
websitecentos.org
irc#centos

People

Translate

site design / logo © 2021 Grokbase