[cisco-voip] DNS client on CUCM, Unity servers?

Wes Sisk wsisk at cisco.com
Mon Sep 28 16:14:10 EDT 2009


Unfortunately, it depends.

With
CSCsq66400    clm rewrites all hosts file entries on subscriber at every 
reboot
the name resolution files such as /etc/hosts were rewritten on every 
reboot.  To accomplish this cluster manager (clm) would attempt 
forward/reverse DNS resolution at every reboot. For versions without the 
fix for CSCsq66400 any reboot with DNS down, incorrect, or unreachable 
will cause informix to not start and therefore critical system failure.

CSCsq66400 should help some and CSCsw88022 should help some more. 
However, this is clearly corner case.  In general if CM is configured 
with DNS then DNS needs to carry same or similar SLA to CM.

/Wes

On Monday, September 28, 2009 4:03:13 PM, Lelio Fulgenzi 
<lelio at uoguelph.ca> wrote:
> Thanks Wes. This really highlights the requirements. I notice the bug 
> you pointed out was only for an upgrade though. Not for actual 
> operations. Do you think CUCM/informix won't start up without DNS 
> after a normal restart?
>
> ---
> Lelio Fulgenzi, B.A.
> Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1
> (519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> "Bad grammar makes me [sic]" - Tshirt
>
>
> ----- Original Message -----
> From: "Wes Sisk" <wsisk at cisco.com>
> To: "Lelio Fulgenzi" <lelio at uoguelph.ca>
> Cc: "cisco-voip mailinglist" <cisco-voip at puck.nether.net>, "Ed 
> Leatherman" <ealeatherman at gmail.com>
> Sent: Monday, September 28, 2009 3:48:30 PM GMT -05:00 US/Canada Eastern
> Subject: Re: [cisco-voip] DNS client on CUCM, Unity servers?
>
> Good points, DNS required for reverse resolution of SIP endpoints.  
> Most presence deployments will use CUPS which has heavy AD dependence 
> which will require AD which will necessitate DNS.  In short, yes, 
> presence will likely require DNS as well.
>
> NAT explanation:
> Whatever is configured under system->server is what gets populated 
> into TFTP configuration files passed to devices.  Since there is 
> nothing out there to fixup XML, and especially encrypted/signed XML 
> files, the hostname would be passed to endpoint.  Endpoint would 
> attempt DNS resolution.  That DNS query would be fixedup to return the 
> outside IP of CUCM.  If you specified an IP under system->server the 
> endpoint would attempt to contact that IP directly.  You could only 
> redirect/NAT that session if you controlled IP routing in the remote 
> subnet.  DNS fixup is a more friendly/transparent option.
>
> AD explanation:
> AD sync must be configured with servername.  Name to IP resolution 
> requires DNS.
>
> /Wes
>
> On Monday, September 28, 2009 3:43:34 PM, Lelio Fulgenzi 
> <lelio at uoguelph.ca> wrote:
>
>     Yowza - Can you elaborate on what you mean by NAT and/or AD?
>
>         * Endpoints doing NAT somewhere out there? Not sure why you'd
>           need DNS for that.
>         * As for AD, do you mean AD/LDAP integration/synchroniation?
>
>     I would have though you need DNS for SIP endpoints, presence, etc.
>
>
>
>     ---
>     Lelio Fulgenzi, B.A.
>     Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1
>     (519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
>     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>     "Bad grammar makes me [sic]" - Tshirt
>
>
>     ----- Original Message -----
>     From: "Wes Sisk" <wsisk at cisco.com>
>     To: "Lelio Fulgenzi" <lelio at uoguelph.ca>
>     Cc: "cisco-voip mailinglist" <cisco-voip at puck.nether.net>, "Ed
>     Leatherman" <ealeatherman at gmail.com>
>     Sent: Monday, September 28, 2009 3:40:39 PM GMT -05:00 US/Canada
>     Eastern
>     Subject: Re: [cisco-voip] DNS client on CUCM, Unity servers?
>
>     If doing NAT or AD it is required.  Otherwise it is still a
>     liability.  Example:
>     CSCsw88022    Database should still start and function when DNS is
>     unavailable
>
>     In this case Informix will not start if configured DNS servers are
>     unreachable.
>
>     /Wes
>
>     On Monday, September 28, 2009 3:33:41 PM, Lelio Fulgenzi
>     <lelio at uoguelph.ca> wrote:
>
>         interesting. is the recommendation still to not enable DNS on
>         CUCM servers?
>
>         ---
>         Lelio Fulgenzi, B.A.
>         Senior Analyst (CCS) * University of Guelph * Guelph, Ontario
>         N1G 2W1
>         (519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
>         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>         "Bad grammar makes me [sic]" - Tshirt
>
>
>         ----- Original Message -----
>         From: "Wes Sisk" <wsisk at cisco.com>
>         To: "Lelio Fulgenzi" <lelio at uoguelph.ca>
>         Cc: "cisco-voip mailinglist" <cisco-voip at puck.nether.net>, "Ed
>         Leatherman" <ealeatherman at gmail.com>
>         Sent: Monday, September 28, 2009 3:31:18 PM GMT -05:00
>         US/Canada Eastern
>         Subject: Re: [cisco-voip] DNS client on CUCM, Unity servers?
>
>         yes, but the dependence on DNS will still affect you
>         intermittently.
>
>         /wes
>
>         On Monday, September 28, 2009 3:28:57 PM, Lelio Fulgenzi
>         <lelio at uoguelph.ca> wrote:
>
>             Wes,
>
>             Can we enable DNS but still program the IP address of the
>             CUCM nodes ?
>
>             ---
>             Lelio Fulgenzi, B.A.
>             Senior Analyst (CCS) * University of Guelph * Guelph,
>             Ontario N1G 2W1
>             (519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
>             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>             "Bad grammar makes me [sic]" - Tshirt
>
>
>             ----- Original Message -----
>             From: "Wes Sisk" <wsisk at cisco.com>
>             To: "Ed Leatherman" <ealeatherman at gmail.com>
>             Cc: "cisco-voip mailinglist" <cisco-voip at puck.nether.net>
>             Sent: Monday, September 28, 2009 3:26:26 PM GMT -05:00
>             US/Canada Eastern
>             Subject: Re: [cisco-voip] DNS client on CUCM, Unity servers?
>
>             Enabling DNS will affect all operations. It's not a
>             component-wise defined feature, think all or nothing.
>
>             All code calls gethostbyname(),
>             gethostbyip(),gethostentry().. which invokes host name
>             resolution features.
>
>             Just make sure:
>             1. forward resolution for all servers work
>             2. reverse resolution for all servers work
>             3. all servers use same dns suffix
>
>             CLI 'set network dns...' is the command set to set and
>             enable dns.
>
>             /Wes
>
>             On Monday, September 28, 2009 3:09:26 PM, Ed Leatherman
>             <ealeatherman at gmail.com> wrote:
>
>                 Follow-up question about DNS..
>
>                 Originally I did not enable DNS on any nodes, as it
>                 was not needed. I would now like to configure an SMTP
>                 server for alerts, and our systems group wants me to
>                 use a name instead of IP. Are there any ramifications
>                 to turning on DNS, regarding things like database
>                 replication or intracluster communications? My servers
>                 are all defined by IP addresses, so it should be using
>                 that through-out, right?
>
>                 I'm assuming various "set network dns*" commands will
>                 turn this on if I decide to do that.
>
>                 On Tue, Aug 18, 2009 at 10:46 AM, Wes Sisk
>                 <wsisk at cisco.com <mailto:wsisk at cisco.com>> wrote:
>
>                     On the surface this seems an odd question so I'm
>                     sure there is misunderstanding.
>
>                     CM needs access to DNS to perform forward and
>                     reverse lookups on:
>                     SIP endpoints
>                     h323 endpoints
>                     AD servers
>                     other nodes in the cluster
>
>                     There are deployments which do not use any of
>                     these and therefore do not need access to a DNS
>                     server.  On those, DNS can be disabled.
>
>                     /Wes
>
>
>                     On Tuesday, August 18, 2009 1:54:37 AM , ciscozest
>                     <ciscozest at gmail.com> <mailto:ciscozest at gmail.com>
>                     wrote:
>
>                         We have 3 CUCM 7.0 servers and only one Unity
>                         Connection 7.0 server.
>
>                         We use a load balancer for IP Phone services
>                         redundancy. There is no integration with any
>                         third party components. When I check our UC
>                         system, I found out that DNS client service is
>                         enabled on both CUCM and Unity servers which I
>                         don’t quite understand why is needed. The
>                         Services URL on CUCM is pointing to load
>                         balancer IP. Would there be any other reason
>                         we have to enable DNS client on CUCM and Unity
>                         server? Also is there a load impact by
>                         enabling DNS client service?
>
>                          
>
>                         Thank you.
>
>                         ------------------------------------------------------------------------
>
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>
>
>                 -- 
>                 Ed Leatherman
>
>
>
>             _______________________________________________ cisco-voip
>             mailing list cisco-voip at puck.nether.net
>             https://puck.nether.net/mailman/listinfo/cisco-voip
>
>
>
>

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