06-20-2008 08:55 AM - edited 03-14-2019 02:25 AM
I have configured the SRV records for two Proxy servers in DNS. It's all working and when the primary CUPS is down, the secondary is used. When both are up, I don't think my priorities are working.
I have both udp and tcp records configured and they specify two A records - the records have equal weight, but one has priority 1 and the other priority 2. I have a strong preference for one CUPS over the other, so this is the way I want this to be, rather than load balancing with equal priorities.
If I call nslookup from a command prompt and type 'set type=SRV' I can query the cluster name OK.
All the details come back correctly, including the weights and priorities. For example:
C:\installed>nslookup
Default Server: us-hqtul-adhp01.ucce.company.icm
Address: 10.10.105.11
> set type=SRV
> _sip._udp.cups.ucce.company.icm
Server: us-hqtul-adhp01.ucce.company.icm
Address: 10.10.105.11
_sip._udp.cups.ucce.company.icm SRV service location:
priority = 2
weight = 10
port = 5060
svr hostname = us-drtul-prhp01.ucce.company.icm
_sip._udp.cups.ucce.company.icm SRV service location:
priority = 1
weight = 10
port = 5060
svr hostname = us-hqtul-prhp01.ucce.company.icm
us-drtul-prhp01.ucce.company.icm internet address = 10.10.202.12
us-hqtul-prhp01.ucce.company.icm internet address = 10.10.102.11
> _sip._udp.cups.ucce.company.icm
Server: us-hqtul-adhp01.ucce.company.icm
Address: 10.10.105.11
_sip._udp.cups.ucce.company.icm SRV service location:
priority = 1
weight = 10
port = 5060
svr hostname = us-hqtul-prhp01.ucce.company.icm
_sip._udp.cups.ucce.company.icm SRV service location:
priority = 2
weight = 10
port = 5060
svr hostname = us-drtul-prhp01.ucce.company.icm
us-hqtul-prhp01.ucce.company.icm internet address = 10.10.102.11
us-drtul-prhp01.ucce.company.icm internet address = 10.10.202.12
> exit
When I do this twice, as shown above, the order changes. But the priorities are such that us-hqtul-prhp01.ucce.company.icm should be first.
I get the same "flipping" of the order if I use the DNS utility from the CVP diagnostic template.
My question is this: is nslookup the way to test this? Should the order oscillate? Is testing out of the diag servlet subject to the same rules?
Regards,
Geoff
06-20-2008 12:43 PM
no the oscillation is not normal.
Is this Microsoft DNS server or linux based (bind?) I have never seen this before.
nslookup is the tool to use.
Is it possible that different DNS Servers are being used, if you have several of them in your TCP configuration for DNS.
One thing to try is run the sniffer like wireshark with the "dns" display filter turned on. it may show something you are not aware of regarding which DNS server you are contacting.
Can you attach a text file that shows your DNS configuration? ie in linux it is a "zone" file.
Another thing to try is find other examples of SRV configurations for your DNS server and stare/compare. There may be something special about the way the records are configured.
06-20-2008 02:15 PM
Good to get a reply. Thanks.
This is Microsoft DNS. There are two DNS servers, Active Directory Domain Controllers for the ICM domain. So the DNS are sync'd.
I am using the two DNS from the client I am running nslookup from. Just a second -- I'll go to just one. Nope, still flips.
The only pictures I have is in the Config guide, and it looks similar.
Are you saying that with a set up like I have, with A record at priority 1 and the other A record at priority 2, nslookup (and the DNS lookup from CVP diag) should always return the records in the same order - the high priority one first?
Regards,
Geoff
06-22-2008 08:44 AM
Hey Geoff,
What I "believe" you want to do is set the priorities to be the same and change the weight to be 100% for one and 0% for the other.
_sip._udp.cups.ucce.company.icm SRV service location:
priority = 1
weight = 100
port = 5060
svr hostname = us-hqtul-prhp01.ucce.company.icm
_sip._udp.cups.ucce.company.icm SRV service location:
priority = 1
weight = 0
port = 5060
Let me know if that works (it should).
adignan - CDW Berbee
*please rate helpful posts
06-22-2008 11:28 AM
Oddly enough, I had some time on my hands this morning, and I have been meaning to configure this in our lab for testing, so I went to try. I can send calls to CUPS6.demo.com (10.1.1.16) and CUPS6-SUB.demo.com (10.1.1.17) by both IP and DNS hostname. However when I configure an SRV records containing these 2 hosts, my call always fails. Is there anything special that needs to be done on either CVP or CUPS to enable SRV functionality? I tried configure Microsoft DNS a few different ways. But _sip._udp.demo.com
port 5060
pri 1
weight 100
host CUPS6.demo.com
_sip._udp.demo.com
port 5060
pri 1
weight 0
host CUPS6-SUB.demo.com
Haven't gotten a call to succeed through it yet. Also I tried using nslookup and everything looks ok. Any suggestions?
Chad
06-22-2008 11:33 AM
When I run nslookup I get
Server:UnKnown ?
This this could be messing things up?
06-22-2008 04:07 PM
Well,
I got DNS SRV working for the primary CUPS proxy. I am running into something strange. My secondary proxy will accept calls into it via IP ONLY when the primary is online. If I shut off the primary, then the calls into the secondary immediatly start failing. CUPS 6.0.1.1000-21... I believe that my DNS SRV is correct now, I just can't test since the backp server won't process calls when the primary is down.
Thanks for the guidance!
Chad
Chad
06-22-2008 08:06 PM
Andy / Geoff,
I see this, and Geoff I don't get accurate tests the way you were doing it, I'm also looking for a good way to test this because I want my routers, and call servers to use there respective Sip Proxy and the way for me to do this yet achieve redundancy is through DNS SRV. If I find a good answer I will let you know, is there maybe a debug to watch packets leaving the router?
Chad
06-22-2008 10:34 PM
From my testing and reading today nslookup is not a valid way of testing priority. Anyways if the priorities are different aka
pri 1 and pri 2
pri 1 will always be chosen if its up!
if they are the same at pri 1 weight 50 and pri 1 weight 50
it will be perfectly load balanced 50 50
if its configured like andry has it the one with weight 100 will always be chosen, same as setting it to priority 1 and priority 2.
HTH,
Chad
06-27-2008 06:31 PM
This is dead easy to test. All you need is a DNS, no CVP needed. I made this test on a Domain Controller while I was idling away my time on the booth at Cisco Live. Quickly added a domain to the forward lookup zone, added SRV records for TCP and UDP with two host names (A records) that already existed. Ran nslookup. Same result.
The specs on SRV say that weights are only examined if priorities are the same. Anyway, nslookup on Windows always alternates the answer.
Still looking for feedback on this.
Regards,
Geoff
06-27-2008 09:40 PM
Geoff, I don't think thats the proper way to test, I think doing a packet capture during a phone call redirecting to see which SIP Proxy is hit is the way to test, I can give this a run through on monday!
Chad
06-28-2008 04:37 AM
I agree that something seems odd with either nslookup or Microsoft DNS. Wireshark is probably a useful strategy. I can tell from the logs on the SIP Proxies which one is being hit. I'll also do some testing on Monday. Cheers.
(PS. I met a couple of your Touchbase mates at Cisco Live.)
Regards,
Geoff
11-02-2008 01:16 AM
Geoff,
I never saw this, you must have met corey and Martin Blake :) Good guys, they flew to The San Fran office after Cisco Live, and I met the for the first time. Also David came from our ofice and was down there. Hopefully next year I will go myself!
Cheers!
Chad
11-02-2008 11:34 AM
Mate, I know Corey from way back when we worked at HP in Brisbane, Oz building Smart Contact. Corey knows a ton of stuff - Touchbase are fortunate to get him. ;-)
Regards,
Geoff
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