[SR-Users] Kamailio Active / Active HA.

[Måns Nilsson]

Subject: Re: [SR-Users] Kamailio Active / Active HA. Date: Mon, Dec 29, 2014 at 11:13:34AM +0000 Quoting Ben Langfeld (ben at langfeld.co.uk):
 
> Just a word of caution here, there are several SIP stacks which don't
> handle SRV lookups correctly. I don't mean to discourage you from this, but
> just to be aware of it. For example, Mobicents only understands SRV record
> sets which return domain names. If you return IPs, Mobicents will go ahead
> and look them up as A records and fail.

I would never, ever, put an IP address in the Target field of a SRV
record. The specification says:

   Target
        The domain name of the target host.  There MUST be one or more
        address records for this name, the name MUST NOT be an alias (in
        the sense of RFC 1034 or RFC 2181).  Implementors are urged, but
        not required, to return the address record(s) in the Additional
        Data section.  Unless and until permitted by future standards
        action, name compression is not to be used for this field.

		RFC2782, p3 

Pretty clear. A host name there should be, resolved to an AAAA/A
record. Mobicents is actually Doing The Right Thing; even though one could
claim the Robustness Principle in favour of the more lenient behaviour,
it is indeed proper to expect to be able to do DNS AAAA/A lookups on
the Target string.

Further, it is a syntax violation to put an IPv6 Address in the Target
field. I made a copy of my zone file and threw in a bogus SRV record. Then
I gave it to the BIND 10 syntax checker, which most predictably barfed
on it:

ball-empfang:tmp mansaxel$ /usr/local/bind10-0a1/sbin/named-checkzone besserwisser.org bsu
bsu:35: warning: 2001:470:28:842:201:2eff:fe48:86aa.besserwisser.org: bad name (check-names)
zone besserwisser.org/IN: _knolk._tcp.besserwisser.org/SRV '2001:470:28:842:201:2eff:fe48:86aa.besserwisser.org' has no address records (A or AAAA)
zone besserwisser.org/IN: loaded serial 2014122801
OK
ball-empfang:tmp mansaxel$ sed -n 35p bsu
_knolk._tcp 10 SRV 0 0 567 2001:470:28:842:201:2eff:fe48:86aa

So, dont! ;-) 

/Måns, who has a population of specialised IP phone devices that most
	certainly won't do SRV.
-- 
Måns Nilsson     primary/secondary/besserwisser/machina
MN-1334-RIPE                             +46 705 989668
LOOK!!  Sullen American teens wearing MADRAS shorts and "Flock of
Seagulls" HAIRCUTS!
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