SIP Enthusiasts!!
Let's look at how an SRV Record is created and what to look for when you are given one.
The SRV record contains more information than the typical DNS record as it contains specific information that can be used to locate a specific resource at an address. This is an example of what an SRV appears like in a typical BIND-style zone file:
_sip._udp.example.com. 86400 IN SRV 0 5 5060 sipserver.example.com.
|__________________||_____||_||____|_|_|____|__________________|
1 2 3 4 5 6 7 8
1 Address - Location of the SRV record, including the resource type (_sip) and protocol (_tcp or _udp) - This information is often given by the provider of the service the SRV is being set up for.
2 TTL - Expiration value of the record.
3 Internet-type - Standard BIND notation indicating that the record is on.
4 InternetRecord type - Standard BIND notation indicating that it’s an SRV record.
5 Priority - Much like an MX record, one is able to set priority of more than 1 record at the address.
6 Weight - There is provision for a rudimentary load balancing schema. All values across all records at the address must add up to 100. The higher the weight, the more often the specific record will be served and vice versa.
7 Port - TCP or UDP port where the specified service can be found.
8 Target Endpoint - the canonical hostname of the machine providing the service.
Now go to:
MX Toolbox SRV LookupFor instance if you go to that link and put the following in the field: _sip._udp.nexvortex.com you will get the following results.
px5.nexvortex.com - 66.23.190.100
px1.nexvortex.com – 66.23.129.253
px7.nexvortex.com – 209.193.79.80
As you can see px3.nexvortex.com is not showing up even though we have that in our default settings in most systems I have done.
If you look at the registrar address. _sip_udp.reg.nexvortex.com you will get the following results.
reg1.nexvortex.com – 66.23.129.110
reg2.nexvortex.com – 66.23.190.120
You can then click the link associated on each one of those and get the actual IP Address associated with them. Now, Nexvortex also has an actual A-Record associated with the base as well so that will give you a completely different IP Address that isn't associated with their SIP service.
If you wanted to do this with NSLOOKUP here is how. Go to Command Line. CMD.EXE and then just look at the entries at the command prompt >
> nslookup
> set type=SRV
> _sip._udp.nexvortex.com
> _sip._udp.reg.nexvortex.com
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Users\sbay>nslookup
Default Server: homeportal
Address: xxxx:xxx:xxxx:xxxx::x
> set type=SRV
> _sip._udp.nexvortex.com
Server: homeportal
Address: xxxx:xxx:xxxx:xxxx::x
Non-authoritative answer:
_sip._udp.nexvortex.com SRV service location:
priority = 30 This server is the last one to take calls.
weight = 0 Not Load Balanced
port = 5060
svr hostname = px7.nexvortex.com
_sip._udp.nexvortex.com SRV service location:
priority = 20 Followed by this server
weight = 0 Not Load Balanced
port = 5060
svr hostname = px5.nexvortex.com
_sip._udp.nexvortex.com SRV service location:
priority = 10 Most of the calls will be taken by this server.
weight = 0 Not Load Balanced
port = 5060
svr hostname = px1.nexvortex.com
> _sip._udp.reg.nexvortex.com
Server: homeportal
Address: xxxx:xxx:xxxx:xxxx::x
Non-authoritative answer:
_sip._udp.reg.nexvortex.com SRV service location:
priority = 10
weight = 0
port = 5070
svr hostname = reg1.nexvortex.com
_sip._udp.reg.nexvortex.com SRV service location:
priority = 20
weight = 0
port = 5070
svr hostname = reg2.nexvortex.com
So, there you have it a simple and easy way to figure out what A-Records are associated with a DNS Service [SRV] record, go forth and be better armed!!
If you are working on a MiVO-250 you can put the A-Records as individual entries inside the Route Sets section of your SIP Peer Configuration as it doesn't support DNS SRV, but you can trick it to do what you need it to do.
Thanks,
TE
