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VIP Purple

VCS Cluster - FQDN and SRV Records

I'm having trouble understanding the VCS Cluster's FQDN and associated SRV records for incoming calls and registrations.

According to the VCS Cluster Deployment Guide:

Example: DNS SRV records for 2 peers of a VCS Expressway cluster for


  • FQDN of VCS Expressway peer 1:
  • FQDN of VCS Expressway peer 2:
  • FQDN of VCS Expressway cluster: 86400 IN SRV 1 1 5061 86400 IN SRV 1 1 5061

    Where does the Cluster's FQDN play a part in the SRV records, and also the cluster peers. It's my understanding that in the above SRV records, would be the SIP domain, not the cluster FQDN.  I understand SRV records, as we have 1 VCS, adding a second to be clustered, so the cluster FQDN is throwing me for a loop.  I've been reading over all the guides and posts here in the forums, but I just can't wrap my head around it. 

    Would the following be correct, looking from the outside going in at the DNS records:

    • FQDN for registrations and/or calls (
      • 86400 IN SRV 1 1 5061
    • VCS Cluster FQDN (
      • 86400 IN SRV 1 1 5061 (VCS Peer1)
      • 86400 IN SRV 1 1 5061 (VCS Peer2)

    I also understand that A records need to be in place for the Cluster FQDN to point to each cluster peer, however they are not shown in this example.


    Everyone's tags (6)
    Cisco Employee

    Re: VCS Cluster - FQDN and SRV Records

    Regarding the example, it is that of the Expressway. In most cases I've seen, the SIP domain is used as the cluster FQDN. For an Expressway, this design is preferred for simplicity. Regarding a VCS Control cluster, there are other things to consider. For example, if Provisioning is enabled on the cluster, do not change the cluster name after enabling Provisioning. The FQDN of the cluster would also be used for load balancing device registration. Normally you would not use the SIP domain as the Control cluster FQDN, as this will already resolve to the Expressway. Once again, a common FQDN for the Control cluster would be for simplicity. What you decide to use is really up to you, and how you want things resolved.

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    VIP Purple

    Re: VCS Cluster - FQDN and SRV Records

    Zac -

    The example is just that, an example, it wasn't directed toward the control or expressway in particular.  Just trying to get an understanding of the cluster FQDN, associated peers, and how they fit in the order of DNS.

    Currently our SIP domain resolves to our single VCS-C, we're working on adding a second C and two VCS-Es, both sets of VCSs will be clustered of course.  In the future after the implentation at a later date, our SIP domain will change to match our organizations domain.

    • In that case, would my example in the orginal post be somewhat correct, if our SIP domain is to be the same as our organization domain (seperate from the VCS-E FQDN)?  In that case it can't exactly resolve directly to the VCS-E cluster, instead the SIP domain would point to the cluster FQDN, and then from there resolve to the cluster peers.
    • Or would the SIP domain point to the peers instead of the cluster FQDN?

    Once I figure out how the order of SRV records go in relation to SIP Domain, Cluster FQDN, Cluster Peers, etc for the Expressway.  Then I'll look at that and include the Control, one thing at a time though.    Like I said, its the inclusion of the cluster FQDN that is messing up in understanding this.

    Cisco Employee

    Re: VCS Cluster - FQDN and SRV Records

    The SRV records for the SIP domain should point to each peer: >>> >>>

    VIP Purple

    Re: VCS Cluster - FQDN and SRV Records

    Thanks Zac!

    The inclusion of the cluster FQDN makes things confusing me. 

    One thing I'm considering is having the E records be the same as the C, of course the addresses would differ.  As you'd go to the VCS that best suites where you're located, being either in the network or outside.  I noticed that was mentioned in the VCS-C/E deployment guide, using internal and external DNS.

    So, to clear up my confusion one last time I think, would the cluster FQDN be used anywhere in the DNS records?  Also where and in what cases, would it be used to point devices to?  It's my understanding that the cluster FQDN would need each peer listed as A records for whatever purpose?

    In my case, until we change our SIP domain to match our organization's domain, I would have a DNS record point it to the cluster FQDN for simplicity.

    Thanks for all the help!

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