[SIPForum-discussion] Question regarding DNS SRV

Anthony Orlando avorlando at yahoo.com
Fri Dec 14 20:56:04 UTC 2007

  You need fixed order A records.  When you query
as.iop1.broadworks.net you should always get as1 back
first then as2.  

--- Jeff Wright <JWright at azteknetworks.net> wrote:

> We are attempting to do some interop testing between
> a Broadsoft proxy,
> and our SIP product which is acting as a B2BUA.  We
> are having issues
> with the implementation of server redundancy in the
> Broadsoft
> configuration.  According to their interop FAQ:
> "BroadWorks uses a Geographic Redundancy model which
> requires DNS SRV to
> support this mechanism.  The Primary Application
> Server (AS) will always
> be the active server hosting the BroadWorks Users.  
> Call state is not
> shared between the primary and secondary Application
> Servers.  If the
> primary AS fails, the access device should send
> further sip requests to
> the next SRV contact, secondary Application server. 
> When the primary
> application server has failed, users will be
> migrated and hosted by the
> secondary application server.  When the primary AS
> is restored, the
> users hosted on the secondary AS will be migrated
> back to the primary
> AS. 
> If the DUT only supports DNS A records the device
> may experience
> requests being toggled between primary and secondary
> Application
> Servers.  If this happens, you'll need to create a
> local DNS with the
> Application Server Cluster FQDN pointing to only the
> primary AS.
> Note:  network devices (i.e., PSTN-terminating
> gateways and
> softswitches) contact the BroadWorks Network Server
> (NS) cluster first
> in a load-sharing manner.   The NS redirects to the
> appropriate AS.  The
> network device must follow the DNS rules above for
> subsequent requests
> to the AS within the dialog, using the FQDN contact
> supplied by the AS."
> We do not support DNS in our product at this time. 
> The overall outcome
> of this is that when we are sending an INVITE to
> start a new call, the
> INVITE is sent to as.iop1.broadworks.net, which
> resolves to
>  What we then observe is that we
> receive a 200 OK with
> SDP, and a contact URI of
> <sip:as.iop1.broadworks.net>, whereupon our
> SIP stack sends an ACK to this sip URI, but: this
> time it resolves to
> and it seems like that server is not
> responding since it
> never received the original INVITE.
> Am I to understand that they expect all user agents
> (which is
> essentially what our product is acting as) to
> implement DNS SRV in order
> to properly interoperate with their proxy?  This
> seems silly to me (or
> perhaps my understanding is too limited), because
> from my perspective,
> DNS is a network-provided service and should not
> have to be built into
> the end user client.
> Thanks in advance for any information anyone can
> provide to help clear
> up this issue.
> Jeffrey D. Wright
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