After 4 (long) days of trying to receive any UDP SIP, I'm hoping
      someone can point out what I'm doing wrong. I've looked at the
      kamailio code. I'm beginning to think it's the 'polling' code, but
      it looks fine. It could be Centos or a Dell network driver, but
      not seeing any errors anywhere.

- stock build/compile...

  Version: kamailio 5.5.2 (x86_64/linux) 0d53d9

  Compile flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS,
      USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP,
      PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY,
      USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE,
      USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLOCKLIST, HAVE_RESOLV_RES

  MAX_RECV_BUFFER_SIZE=262144

  MAX_URI_SIZE=1024

  BUF_SIZE=65535

  DEFAULT PKG_SIZE=8MB

  DEFAULT SHM_SIZE=64MB

  ADAPTIVE_WAIT_LOOPS=1024

  TCP poll methods: poll, epoll_lt, epoll_et, sigio_rt,
      select

  Source code revision ID: 0d53d9

  Compiled with: gcc 4.8.5

  Compiled architecture: x86_64

  Compiled on: 08:44:19 Oct 11 2021

Running Centos 7 all updated. Dell R630.

# sestatus

SELinux status:                 disabled

# firewall-cmd --list-all

  ports: 5666/tcp 873/tcp 873/udp 80/tcp 443/tcp 5060/tcp
      5060/udp 5061/tcp 5061/udp

- Just trying to send SIP INVITE from trunk provider to
      R630 kamailio.
..

(SIP trunk) UDP 172.200.200.202:5060 -> (firewall) UDP
      172.250.250.162:5060 -> 1:1 NAT -> (R630) UDP
      10.102.88.81:5060

- I can 'see' the packet hit the em3 network...

#  tcpdump -i em3 -e -vv -n port 5060

11:53:33.260892 99:99:ef:3e:69:c1 > 99:99:1c:48:4e:e3,
      ethertype IPv4 (0x0800), length 1366: (tos 0x0, ttl 54, id 20430,
      offset 0, flags [none], proto UDP (17), length 1352)

    172.200.200.202.sip > 10.102.88.81.sip: [udp sum ok]
      SIP, length: 1324

    INVITE sip:+18005551234@172.250.250.162:5060 SIP/2.0

          ...

At this point, I just need to see a SIP INVITE received.
      Then I can go back to working on a real config.

I've tried with TCP on/off, listening on all networks,
      alias on/off, strace and everything else I could think of.

      Truly appreciate any guidance.

Tried every sample config possible, but I just need to test
      receiving the SIP UDP packet, so this 'should' be minimum
      config...

#!KAMAILIO

debug=9

log_stderror=no

log_facility=LOG_LOCAL0

log_prefix="{$mt $hdr(CSeq) $ci} "

children=2

disable_tcp=yes

udp4_raw=on

auto_aliases=no

alias="sbc01.mysite.com"

listen=udp:10.102.88.81:5060

loadmodule "debugger.so"

loadmodule "jsonrpcs.so"

loadmodule "kex.so"

loadmodule "corex.so"

loadmodule "sl.so"

loadmodule "rr.so"

loadmodule "pv.so"

loadmodule "textops.so"

loadmodule "siputils.so"

loadmodule "xlog.so"

loadmodule "sanity.so"

loadmodule "ctl.so"

loadmodule "cfg_rpc.so"

modparam("debugger", "cfgtrace", 1)

request_route {

  xlog("SIP received xxxxxxxxxxxxxxxxxxx\n");

}

      # kamcmd ps

      11578    main process - attendant

      11579    udp receiver child=0 sock=10.102.88.81:5060

      11580    udp receiver child=1 sock=10.102.88.81:5060

      11581    slow timer

      11583    timer

      11584    secondary timer

      11585    JSONRPCS FIFO

      11586    JSONRPCS DATAGRAM

      11587    ctl handler

- I get plenty of logging, but the logging just waits
      here...

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      INFO: ctl [io_listener.c:210]: io_listen_loop(): io_listen_loop:
      using epoll_lt as the io watch method (auto detected)

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      DEBUG: <core> [core/mem/q_malloc.c:374]: qm_malloc():
      qm_malloc(0x7fd2a8bae010, 4800) called from core: core/io_wait.c:
      init_io_wait(469)

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10059]:
      DEBUG: <core> [core/mem/q_malloc.c:419]: qm_malloc():
      qm_malloc(0x7fd2a8bae010, 65456) returns address 0x7fd2a8c652d8
      frag. 0x7fd2a8c652a0 (size=65456) on 1 -th hit

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      DEBUG: <core> [core/mem/q_malloc.c:419]: qm_malloc():
      qm_malloc(0x7fd2a8bae010, 4800) returns address 0x7fd2a8c652d8
      frag. 0x7fd2a8c652a0 (size=4800) on 1 -th hit

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      DEBUG: <core> [core/mem/q_malloc.c:374]: qm_malloc():
      qm_malloc(0x7fd2a8bae010, 2400) called from core: core/io_wait.c:
      init_io_wait(516)

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      DEBUG: <core> [core/mem/q_malloc.c:419]: qm_malloc():
      qm_malloc(0x7fd2a8bae010, 2400) returns address 0x7fd2a8c66600
      frag. 0x7fd2a8c665c8 (size=2400) on 1 -th hit

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      DEBUG: ctl [io_listener.c:246]: io_listen_loop(): io_listen_loop:
      adding socket 8, type 2, transport 3
      (/var/run/kamailio//kamailio_ctl)

Oct 12 11:38:04 sbc01 /usr/local/sbin/kamailio[10060]:
      DEBUG: ctl [../../core/io_wait.h:375]: io_watch_add(): DBG:
      io_watch_add(0x7fd2a70a5360, 8, 2, 0x2439960), fd_no=0

      - The only other thing that I see is transport 3. Isn't that a 
UNIXS_SOCK?