[sr-dev] [tracker] Task opened: DNS SRV balancing doesn't work

[sip-router]

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A new Flyspray task has been opened.  Details are below. 

User who did this - Alex Hermann (axlh) 

Attached to Project - sip-router
Summary - DNS SRV balancing doesn't work
Task Type - Bug Report
Category - dns / dns cache
Status - Assigned
Assigned To - Andrei Pelinescu-Onciul
Operating System - All
Severity - High
Priority - Normal
Reported Version - 3.1
Due in Version - Undecided
Due Date - Undecided
Details - Request to a domain served by SRV records all go to the same host.


The domain is as follows:
<code>
_sip._udp.srv.test. 44 IN    SRV     10 0 5060 172.28.4.250.
_sip._udp.srv.test. 44 IN    SRV     10 0 5061 172.28.4.251.
_sip._udp.srv.test. 44 IN    SRV     10 0 5062 172.28.4.252.
_sip._udp.srv.test. 44 IN    SRV     10 0 5063 172.28.4.253.
</code>

Expected behavior would be that each host would receive an (approximate) equal amount of requests. in practice, one of them gets them all. The winning host changes after most restarts of kamailio, which suggests the randomization is done only once instead of for every request as is necessary.

DNS related settings:
<code>
dns_use_search_list=no
use_dns_failover=yes
dns_srv_lb=yes
</code>

Results from a run of 20 (near simultaneous) calls to the above domain (format <call-number> <destination>):

<code>
1 172.28.4.251:5061
2 172.28.4.251:5061
3 172.28.4.251:5061
4 172.28.4.251:5061
5 172.28.4.251:5061
6 172.28.4.251:5061
7 172.28.4.251:5061
8 172.28.4.251:5061
9 172.28.4.251:5061
10 172.28.4.251:5061
11 172.28.4.251:5061
12 172.28.4.251:5061
13 172.28.4.251:5061
14 172.28.4.251:5061
15 172.28.4.251:5061
16 172.28.4.251:5061
17 172.28.4.251:5061
18 172.28.4.251:5061
19 172.28.4.251:5061
20 172.28.4.251:5061

1 172.28.4.250:5060
2 172.28.4.250:5060
3 172.28.4.250:5060
4 172.28.4.250:5060
5 172.28.4.250:5060
6 172.28.4.250:5060
7 172.28.4.250:5060
8 172.28.4.250:5060
9 172.28.4.250:5060
10 172.28.4.250:5060
11 172.28.4.250:5060
12 172.28.4.250:5060
13 172.28.4.250:5060
14 172.28.4.250:5060
15 172.28.4.250:5060
16 172.28.4.250:5060
17 172.28.4.250:5060
18 172.28.4.250:5060
19 172.28.4.250:5060
20 172.28.4.250:5060

1 172.28.4.253:5063
2 172.28.4.253:5063
3 172.28.4.253:5063
4 172.28.4.253:5063
5 172.28.4.253:5063
6 172.28.4.253:5063
7 172.28.4.253:5063
8 172.28.4.253:5063
9 172.28.4.253:5063
10 172.28.4.253:5063
11 172.28.4.253:5063
12 172.28.4.253:5063
13 172.28.4.253:5063
14 172.28.4.253:5063
15 172.28.4.253:5063
16 172.28.4.253:5063
17 172.28.4.253:5063
18 172.28.4.253:5063
19 172.28.4.253:5063
20 172.28.4.253:5063

1 172.28.4.252:5062
2 172.28.4.252:5062
3 172.28.4.252:5062
4 172.28.4.252:5062
5 172.28.4.252:5062
6 172.28.4.252:5062
7 172.28.4.252:5062
8 172.28.4.252:5062
9 172.28.4.252:5062
10 172.28.4.252:5062
11 172.28.4.252:5062
12 172.28.4.252:5062
13 172.28.4.252:5062
14 172.28.4.252:5062
15 172.28.4.252:5062
16 172.28.4.252:5062
17 172.28.4.252:5062
18 172.28.4.252:5062
19 172.28.4.252:5062
20 172.28.4.252:5062
</code>


More information can be found at the following URL:
http://sip-router.org/tracker/index.php?do=details&task_id=120

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