Our IMS clients will use DNS service to resolve which transport protocol to preferr and which server provides that SIP service. Therefore we need for this purpose working DNS server with valid delegated zones. In our case we are administrating own DNS zone named ims1.sip.uniza.sk. So we will add required resource records, first we add NAPTR records and then valid SRV and A records

So, prepare your DNS records, in our case:

$ORIGIN ims1.sip.uniza.sk.
@               NAPTR 30 100 "S" "SIP+D2U" "" _sip._udp.pcscf.ims1.sip.uniza.sk.
@               NAPTR 20 100 "S" "SIP+D2T" "" _sip._tcp.pcscf.ims1.sip.uniza.sk.
@               NAPTR 10 100 "S" "SIP+D2T" "" _sip._tcp.pcscf.ims1.sip.uniza.sk.
pcscf           IN      A       158.193.139.40
_sip.pcscf      IN      SRV 0 0 5060 pcscf
_sip._udp.pcscf IN      SRV 0 0 5060 pcscf
_sip._tcp.pcscf IN      SRV 0 0 5060 pcscf
_sips._tcp.pcscfIN     SRV 0 0 5060 pcscf
icscf           IN      A       158.193.139.41
_sip            IN      SRV 0 0 5060 icscf
_sip._udp       IN      SRV 0 0 5060 icscf
_sip._tcp       IN      SRV 0 0 5060 icscf
scscf           IN      A       158.193.139.42
_sip.scscf      IN      SRV 0 0 5060 scscf
_sip._udp.scscf IN      SRV 0 0 5060 scscf
_sip._tcp.scscf IN      SRV 0 0 5060 scscf
hss             IN      A       158.193.139.43
presence        IN      A     158.193.139.37