I have configured kamailio as an IMS server as VM based .

PCSCF - 10.x.x.179

ICSCF - 10.x.x.79

SCSCF - 10.x.x.73

HSS - 10.x.x.75

I am using zoiper client for testing the call flow . The registration is happening properly in my both zoiper clients for hss configured users (alice and bob).

When i am making an INVITE , I am getting 403 Forbidden - Domain not served error from SCSCF.

The Call Flow for invite is as follows . call from alice@sip.example.com

zoiper1 (UE) -> PCSCF ( INVITE sip:bob@sip.example.com;transport=UDP )

PCSCF -> SCSCF (  INVITE sip:bob@sip.example.com;transport=UDP )

SCSCF -> PCSCF (100 trying)

SCSCF -> ICSCF   ( INVITE sip:bob@sip.example.com;transport=UDP )

ICSCF -> SCSCF (100 trying)

ICSCF -> SCSCF ( INVITE sip:bob@sip.example.com;transport=UDP )

SCSCF -> ICSCF (100 trying)

SCSCF -> ICSCF (403 Forbidden - Domain not served)

ICSCF -> SCSCF (Request: ACK sip:bob@sip.example.com | )

ICSCF -> SCSCF ( 403 Forbidden - Domain not served )

SCSCF -> PCSCF ( 403 Forbidden - Domain not served )

PCSCF -> UE ( 403 Forbidden - Domain not served )

Below are the alias configuration i have done in pcscf,icscf,scscf nodes

# IP-Adress for incoming SIP-Traffic, in the following format:

# SIP / UDP
listen=udp:10.x.x.179:4060
# SIP / TCP
listen=tcp:10.x.x.179:4060
# SIP / TCP/TLS
listen=tls:10.x.x.179:4060

# IPSEC / UDP
#!define IPSEC_LISTEN_ADDR "0.0.0.0"
#!define IPSEC_CLIENT_PORT 5062
#!define IPSEC_SERVER_PORT 5063
#alias="sip.example.com:4060"
alias=pcscf.sip.example.com:4060

#!define MY_WS_PORT 80
#!define MY_WSS_PORT 443

#!define PCSCF_URL "sip:pcscf.sip.example.com:4060"

#!define TCP_PROCESSES 8

#!subst "/NETWORKNAME/sip.example.com/"
#!subst "/HOSTNAME/pcscf.sip.example.com/"

# SIP / UDP
listen=udp:10.x.x.79:4070
# SIP / TCP
listen=tcp:10.x.x.79:4070
# SIP / TCP/TLS
listen=tls:10.x.x.79:4071

alias="icscf.sip.example.com:4070"

#!define NETWORKNAME "sip.example.com"
#!define HOSTNAME "icscf.sip.example.com"

# SIP / UDP
listen=udp:10.x.x.73:4080
# SIP / TCP
listen=tcp:10.x.x.73:4080
# SIP / TCP/TLS
listen=tls:10.x.x.73:4081

#!define NETWORKNAME "sip.example.com"
#!define HOSTNAME "scscf.sip.example.com"
#!define URI "sip:scscf.sip.example.com:4080"
alias=scscf.sip.example.com:4080

# ENUM-Server to query:
#!define ENUM_SUFFIX "scscf.sip.example.com."

Kindly let me know where i am missing . Kindly need help in this issue since the registration is happening successfully and dropping in the INVITE level.

Kindly help.