Description

We tried to load share 50+ media servers using dispatching algorithm 11 and faced an unexpected behavior when most calls go to very first host in the group.

Troubleshooting

I tried to start Kamailio like this:
sudo kamailio -f /etc/kamailio/kamailio.cfg -E -d 5 -u 995
but errors were the same when dispatcher group had more than 25 and less than 25 hosts

It was tried different combinations of dispatcher list host group configuration:
100 sip:10.60.27.123:7000 10 rweight=50

100 sip:10.60.27.123:7000 10 weight=50;rweight=50

100 sip:10.60.27.123:7000 rweight=50,maxload=80

When making 100 calls the quarter of them go to the first host in the group.

Reproduction

modparam("dispatcher", "list_file", "/etc/kamailio/dispatcher.list")
modparam("dispatcher", "flags", 2)
modparam("dispatcher", "ds_ping_method", "OPTIONS")
modparam("dispatcher", "ds_probing_threshold", 3)
modparam("dispatcher", "ds_inactive_threshold", 10)
modparam("dispatcher", "ds_probing_mode", 3)
modparam("dispatcher", "ds_ping_interval", 10)
modparam("dispatcher", "ds_ping_reply_codes", "501,403,404,400,200")
modparam("dispatcher", "ds_ping_from",DS_PING_FROM_PARAM)
modparam("dispatcher", "use_default", 0)

if ( ds_is_from_list("101")) {
sl_send_reply("100","My calls");
ds_select_dst("100", "11");
return;
}

Dispatcher group must have more than 25 hosts, if equal or less than 25 than it is Ok:
100 sip:10.60.27.123:7000 0 10 rweight=50
100 sip:10.60.27.123:7001 0 10 rweight=50
100 sip:10.60.27.123:7002 0 10 rweight=50
100 sip:10.60.27.123:7003 0 10 rweight=50
100 sip:10.60.27.123:7004 0 10 rweight=50
100 sip:10.60.27.123:7005 0 10 rweight=50
100 sip:10.60.27.123:7006 0 10 rweight=50
100 sip:10.60.27.123:7007 0 10 rweight=50
100 sip:10.60.27.123:7008 0 10 rweight=50
100 sip:10.60.27.123:7009 0 10 rweight=50
100 sip:10.60.27.123:7010 0 10 rweight=50
100 sip:10.60.27.123:7011 0 10 rweight=50
100 sip:10.60.27.123:7012 0 10 rweight=50
100 sip:10.60.27.123:7013 0 10 rweight=50
100 sip:10.60.27.123:7014 0 10 rweight=50
100 sip:10.60.27.123:7015 0 10 rweight=50
100 sip:10.60.27.123:7016 0 10 rweight=50
100 sip:10.60.27.123:7017 0 10 rweight=50
100 sip:10.60.27.123:7018 0 10 rweight=50
100 sip:10.60.27.123:7019 0 10 rweight=50
100 sip:10.60.27.123:7020 0 10 rweight=50
100 sip:10.60.27.123:7021 0 10 rweight=50
100 sip:10.60.27.123:7022 0 10 rweight=50
100 sip:10.60.27.123:7023 0 10 rweight=50
100 sip:10.60.27.123:7024 0 10 rweight=50

To emulate call load and multiple media servers, SIPp scenarios were used.

Debugging Data

Log Messages

SIP Traffic

No specific traffic, regular INVITE messages having international numbers.

Possible Solutions

Additional Information

kamailio -v
version: kamailio 5.4.4 (x86_64/linux) e16352
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_BLACKLIST, HAVE_RESOLV_RES
ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB
poll method support: poll, epoll_lt, epoll_et, sigio_rt, select.
id: e16352 
compiled on 15:56:46 Feb 15 2021 with gcc 4.8.5

CentOS Linux release 7.7.1908 (Core)

Linux test-carrier-1.prd.tc5.ams.nl.kwebbl.loc 3.10.0-1062.4.1.el7.x86_64 #1 SMP Fri Oct 18 17:15:30 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

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