dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
16848
share rss forum feed


TSI Marc
Premium,VIP
join:2006-06-23
Chatham, ON
kudos:28
reply to koitsu

Re: Google DNS versus ours

said by koitsu:

Marc, politely: I've had two other senior systems engineers (like myself) look at the graph. Both of them are equally as perplexed, and in the same way I am.

...

Not trying to troll or give you a headache, mate!

Hey no worries didn't mean to come off like that.. I'm a mechanical engineer and built and ran our network for 10 years.. the graph makes sense to me, I just assumed it did to others too.

All good though man, appreciate the feedback, I know it's coming from a good place. I'm happy we were able to tweak a bit more performance on this front. Seems we're all excited about that
--
Marc - CEO/TekSavvy


Teddy Boom
k kudos Received
Premium
join:2007-01-29
Toronto, ON
kudos:21

1 recommendation

reply to koitsu
said by koitsu:

Except if you apply the same logic to the data shown on the rights side of the graph, you could safely say that 97% of all queries took 200ms to get a result...

It is essentially a Cumulative Distribution Function:
»en.wikipedia.org/wiki/Cumulative···function

The right side of the graph says that 97% of all queries took less than 200ms to get a result.
--
electronicsguru.ca/for_sale/Cablemodems


d4m1r

join:2011-08-25
Reviews:
·Start Communicat..

1 edit
reply to TSI Gabe
Interesting and thanks for the information....

However, it is still always better to use a 3rd party DNS service anyway (even at a slight ms hit) because;

1) Privacy reasons. You want to fragment your services as much as possible.

2) Larger DNS providers like OpenDNS have larger CDN networks in place than a local ISP running a few Akamai servers.

Just my 2 cents....
--
www.613websites.com Budget Canadian Web Design and Hosting

Jonathan987

join:2006-03-17
North York, ON
interesting point, I'd add to that you can also use DNScrypt with opendns
Here's the thread I posted about it: »DNSCrypt for Teksavvy users?

Gabe is there any chance you could implement DNScrypt with the new DNS servers? I'm hoping to make use of the new Tek DNS servers

Thanks!

wally_walrus

join:2009-10-07
Orleans, ON
reply to TSI Gabe
Hello TSI Gabe,

Could you please tell if TSI DNS servers properly respond to DNS SRV queries as needed for correct SIP support? My VoIP provider (Callcentric) are currently experiencing major issues, and one of their suggestion to mitigate impact was to use 3rd party DNS servers as some don't properly resolve DNS SRV queries. This is copied from their status update page:

Update 10/19 - DNS SRV

We have received reports that some users are having problems using our DNS SRV based servers.

This is specifically because the new list of servers returned is not properly parsed by some DNS servers due to the size of the information, or not being returned at all. As such, we recommend using different DNS servers in your router and/or device if you are experiencing problems.

We have tested the servers below and found that they resolve our SRV records properly:

xxx.xxx.xx.x
xxx.xxx.xx.x


n3k0

@teksavvy.com
+1

Same problem on my end. Had to use DNS servers supplied on CC's webpage, within my device, to resolve.

Using Teksavvy's DNS servers resulted in registration failure on my device.

OTIS3

join:2011-09-29
I was having lots of trouble with callcentric as well. both their recommend opendns and teksavvy were failing. i had to disable these two options to get it working again.

Use DNS SRV
DNS SRV Auto Prefix

wally_walrus

join:2009-10-07
Orleans, ON
They say it should work with either DNS SRV or not, and mine is still using it and registers properly. Teksavvy's DNS weren't working with DNS SRY set to yes. When I changed to their recommended DNS servers in my 3102 it started working.

Can we have an detailed answer from Teksavvy on this one?

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..
reply to TSI Marc
I've been re-testing TSI DNS since this thread began, and thus far it hasn't failed on any sites for us (a record for TSI DNS here), and seems plenty quick enough now.

So TSI is now number one on the "Forwarders" list for our local DNS.
Good stuff, guys!


TSI Gabe
Router of Packets
Premium,VIP
join:2007-01-03
Gatineau, QC
kudos:7
I can take a look but it would be really useful if you guys could provide me with a hostname to test against.

wally_walrus

join:2009-10-07
Orleans, ON
callcentric.com

or

srv.callcentric.com

wally_walrus

join:2009-10-07
Orleans, ON
Also could you please provide us with a method to test for this in the future? I'd really like to have all devices behind my router use the default servers (hopefully Teksavvy), instead of configuring different DNS servers on each and every one


neko
All Hail Canada
Premium
join:2006-08-11
Canada
Reviews:
·TekSavvy Cable
reply to TSI Gabe
callcentric.com works & resolves through Teksavvy DNS, but that isn't the recommended solution from CallCentric.

They recommend using: srv.callcentric.com

That does not get resolved & causes my device to fail in registering with CallCentric. I had to use different DNS in the configuration of my device to have it correctly resolve the srv.callcentric.com

As Wally_Walrus said, i'd prefer to have it resolve using Teksavvy DNS, than having to hardcode an alternate into my device.

For reference:

Callcentric Problems Using ISP Assigned DNS

Callcentric DDOS Mega Thread
--
...virtue gives you heraldry.

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..
MMmm.. the problem appears to be not with Teksavvy, but rather with callcentric's DNS provider (telengy.net):

$ whois callcentric.com
...
Domain servers in listed order:
NS1.TELENGY.NET 66.193.176.41
NS2.TELENGY.NET 204.11.192.20
NS3.TELENGY.NET 204.11.192.68
...

$ nslookup
> server ns1.telengy.net
Default server: ns1.telengy.net
Address: 66.193.176.41#53

> callcentric.com
Server: ns1.telengy.net
Address: 66.193.176.41#53

Name: callcentric.com
Address: 204.11.192.22
Name: callcentric.com
Address: 204.11.192.23
Name: callcentric.com
Address: 204.11.192.31
Name: callcentric.com
Address: 204.11.192.34
Name: callcentric.com
Address: 204.11.192.35
Name: callcentric.com
Address: 204.11.192.36
Name: callcentric.com
Address: 204.11.192.37
Name: callcentric.com
Address: 204.11.192.38
Name: callcentric.com
Address: 204.11.192.39
Name: callcentric.com
Address: 204.11.192.135
Name: callcentric.com
Address: 204.11.192.159
Name: callcentric.com
Address: 204.11.192.160

> srv.callcentric.com
Server: ns1.telengy.net
Address: 66.193.176.41#53

Non-authoritative answer:
*** Can't find srv.callcentric.com: No answer

> server ns2.telengy.net
Default server: ns2.telengy.net
Address: 204.11.192.20#53

> srv.callcentric.com
Server: ns2.telengy.net
Address: 204.11.192.20#53

*** Can't find srv.callcentric.com: No answer


neko
All Hail Canada
Premium
join:2006-08-11
Canada
Reviews:
·TekSavvy Cable
Here is a guy explaining what's happening:

»DNS SRV - Callcentric

Hopefully you'll understand what he's on about, as I do not.

All I know for sure is Tekk's DNS doesn't allow my device to register & make calls; using an alternate DNS provider does work.

I'm sorry I can't be more helpful, as I have no clue about all this stuff.
--
...virtue gives you heraldry.

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..
The discussion at that link is NOT looking for srv.callcentric.com at all.
Instead, they are using _sip._udp.callcentric.com. for the hostname.

Perhaps that's part of your problem?
The (successful) query below is using Teksavvy DNS:

[~] dig @206.248.154.22 _sip._udp.callcentric.com SRV
;; Truncated, retrying in TCP mode.

; > DiG 9.7.0-P1 > @206.248.154.22 _sip._udp.callcentric.com SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER- opcode: QUERY, status: NOERROR, id: 54216
;; flags: qr rd ra; QUERY: 1, ANSWER: 24, AUTHORITY: 3, ADDITIONAL: 12

;; QUESTION SECTION:
;_sip._udp.callcentric.com. IN SRV

;; ANSWER SECTION:
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha1.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha2.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha3.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha4.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha5.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha6.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha7.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha8.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha9.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha10.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha11.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 5080 alpha12.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha1.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha2.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha3.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha4.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha5.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha6.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha7.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha8.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha9.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha10.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha11.callcentric.com.
_sip._udp.callcentric.com. 51 IN SRV 20 0 10123 alpha12.callcentric.com.

;; AUTHORITY SECTION:
callcentric.com. 58 IN NS ns2.telengy.net.
callcentric.com. 58 IN NS ns3.telengy.net.
callcentric.com. 58 IN NS ns1.telengy.net.

;; ADDITIONAL SECTION:
alpha1.callcentric.com. 51 IN A 204.11.192.22
alpha2.callcentric.com. 58 IN A 204.11.192.23
alpha3.callcentric.com. 58 IN A 204.11.192.31
alpha4.callcentric.com. 51 IN A 204.11.192.34
alpha5.callcentric.com. 51 IN A 204.11.192.35
alpha6.callcentric.com. 51 IN A 204.11.192.36
alpha7.callcentric.com. 51 IN A 204.11.192.37
alpha8.callcentric.com. 51 IN A 204.11.192.38
alpha9.callcentric.com. 51 IN A 204.11.192.39
alpha10.callcentric.com. 59 IN A 204.11.192.135
alpha11.callcentric.com. 51 IN A 204.11.192.159
alpha12.callcentric.com. 51 IN A 204.11.192.160

;; Query time: 16 msec
;; SERVER: 206.248.154.22#53(206.248.154.22)
;; WHEN: Sun Oct 21 15:37:16 2012
;; MSG SIZE rcvd: 1401

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..
Ah, but even with the correct hostname (_sip._udp.callcentric.com), there's still a problem with Teksavvy DNS: they don't return ANY results when "truncating" the response. This prevents voip devices (ATAs) from working at all unless the device supports TCP DNS lookups (not all do).

[~] dig @206.248.154.22 _sip._udp.callcentric.com SRV +notcp +noignore

; > DiG 9.7.0-P1 > @206.248.154.22 _sip._udp.callcentric.com SRV +notcp +noignore
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER- opcode: QUERY, status: NOERROR, id: 32860
;; flags: qr tc rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;_sip._udp.callcentric.com. IN SRV

;; Query time: 30 msec
;; SERVER: 206.248.154.22#53(206.248.154.22)
;; WHEN: Sun Oct 21 15:43:19 2012
;; MSG SIZE rcvd: 43


neko
All Hail Canada
Premium
join:2006-08-11
Canada
Reviews:
·TekSavvy Cable
said by mlord:

Ah, but even with the correct hostname (_sip._udp.callcentric.com), there's still a problem with Teksavvy DNS: they don't return ANY results when "truncating" the response. This prevents voip devices (ATAs) from working at all unless the device supports TCP DNS lookups (not all do).

So it is their problem, & not ours?

That's all we wanted Gabe to know. That Tek's DNS doesn't work for our VOIP device settings.

Hopefully a fix can be made.
--
...virtue gives you heraldry.

mlord

join:2006-11-05
Nepean, ON
kudos:13
Well, the real problem is callcentric.com. putting "too much" data into their DNS entry. Teksavvy *could* help out by having their DNS return partial (truncated) results to the UDP query, but they're not required to by any internet standards.


TSI Gabe
Router of Packets
Premium,VIP
join:2007-01-03
Gatineau, QC
kudos:7
honestly I kinda hate doing this but I agree with mlord... the problem is that the record is too large therefore requires the use of TCP....knowing that most ATAs don't support this they are kind of shooting themselves in the foot.

What's even more questionable is that they expect the DNS entry to be truncated...so why not enter fewer SRV records in to begin with to allow UDP to work?

I'm not saying I don't want to fix this...fixing it though on the other end would be IMO a big hack and not even sure that this would really be RFC compliant....

luckily though I'm at NANOG right now and am surrounded by geeks that deal with this on a daily basis...I'll ask around when I get the chance.
--
TSI Gabe - TekSavvy Solutions Inc.
Authorized TSI employee ( »TekSavvy FAQ »Official support in the forum )

jabley

join:2012-10-21
London, ON
There are several things going on, here.

The resource record set (RRSet) that the ATA is looking for is unusually large. Large responses in the DNS are generally accommodated by either negotiating a large UDP response buffer with EDNS0 (see RFC 2671) or by setting the truncate bit (TC) to 1 in a response and forcing a second DNS request using TCP.

Both these approaches have problems. Large UDP buffer sizes result in fragmentation, and fragmentation can be problematic. Many firewalls and other middleware make bad assumptions about 53/tcp, and hence TCP requests don't always work.

So, solution 1: if I was callcentral, I would be reducing my response to that particular query to ensure that it fits in a 512 byte DNS response message without truncation. If they chose their server names more carefully they could still pack a good number of resource records in the ANSWER section by taking better advantage of label compression.

The ATA described here appears not to support EDNS0 or TCP, so it has no capability of receiving large (complete) DNS responses. Not supporting TCP means not following the specification. The ATA is definitively broken, here. It violates RFC 1035. (I realise it's not unique in that. There are lots of bad DNS implementations in the world.)

Solution 2: fix the ATA. It's broken. The fact that it has ever worked is a happy accident.

BIND9's behaviour when it falls back to TCP is to set TC=1 in the response header, and to populate the answer section with as much as will fit. This response is intended to be interpreted as "this is not an accurate response, but here is a partial answer and you should use TCP to get the rest of it".

Unbound's behaviour is not to return partial responses. It says "I can't give you a complete response, and I'm not going to risk giving you a partial answer because that might be bad, so you need to use TCP".

Needless to say, this level of detail (how to populate the ANSWER section in a truncated response) is not really specified in RFC 1035, which is old. Technically, I think it's fair to say that both unbound and BIND9 are following the specification, as far as it goes.

BIND9's behaviour here is more forgiving of the broken DNS code in the ATA. I don't see an option in unbound to emulate the BIND9 approach to this.

Solution 3: choose different nameservers that behave as BIND9 does.

Unbound is good, polished software in my opinion. It has performance advantages and is far harder to fool with cache poisoning attacks than BIND9. It's hard to argue that the correct solution here is to replace unbound with BIND9; in effect, that would be throwing out the benefits of unbound for all users simply to accommodate one buggy ATA that is used by a tiny minority.

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..
reply to TSI Gabe
said by TSI Gabe:

luckily though I'm at NANOG right now and am surrounded by geeks that deal with this on a daily basis...I'll ask around when I get the chance.

Sounds like the Right Crowd to find a solution with, but I'm with you on this one -- risky to modify the DNS behaviour to accommodate a clueless voip provider, especially as there's a definite risk of breaking other stuff.

Don't forget to go out for some Real Beef BBQ down that way, and let us all know if you manage to reverse engineer the famous fountains down town (if you grok the pattern, you can stride up the middle without getting wet!).

Cheers!

OTIS3

join:2011-09-29
reply to jabley
said by jabley:

simply to accommodate one buggy ATA that is used by a tiny minority.

I don't think anyone has specifically mentioned any ATA models yet in this thread. For me personally, I'm using a Linksys PAP2T which is probably the most widely deployed ATA for home users. I'm not saying it is good or that Linksys/Cisco isn't known for having buggy devices. They are also not likely to fix it in a new firmware at this point.

wally_walrus

join:2009-10-07
Orleans, ON
+1. Even though some / most models are "buggy" they are widely used, so efforts should be made to support them. I am using an SPA-3102

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..
said by wally_walrus:

+1. Even though some / most models are "buggy" they are widely used, so efforts should be made to support them.

+100

The PAP2T are very likely the most common "non locked" ATA devices out there, with their cousins the SPA-3102 also fairly prevalent.

So it's not feasible to simply ignore them. Callcentric.com needs to do better.

Meanwhile, anyone affected by this can just use a different DNS service, or run a copy of bind9 locally to relay from Teksavvy DNS without the issue of Teksavvy DNS.

I just checked here, and my local bind9 service does return partial results just fine, but the stripped down DNS in my router does not. I imagine that folks running OpenWRT on their routers would have the option of adding bind9 service onto those, which would take care of it as well.

Cheers

mlord

join:2006-11-05
Nepean, ON
kudos:13
Reviews:
·Start Communicat..

1 edit
said by mlord:

Meanwhile, anyone affected by this can just use a different DNS service, or run a copy of bind9 locally to relay from Teksavvy DNS without the issue of Teksavvy DNS.

Or maybe TSI Gabe could channel the spirit of Teksavvy Past, and run bind9 on one server internally (doesn't need to be accessible outside of Teksavvy), and have it act as the authority for Callcentric.com for use by Teksavvy's public DNS servers. Hacky, and there are probably other similar/better workarounds that TSI Gabe could dream up.


TSI Gabe
Router of Packets
Premium,VIP
join:2007-01-03
Gatineau, QC
kudos:7
Well jabley See Profile is with me at NANOG and his reply here is what came out of the conversation we had. The reality here is that clearcable is knowingly serving a large RRSET that doesn't fit in a 512 byte buffer and they also know that this results in a half broken DNS reply when using a few well known ATAs. I've also talked to a few more people, some of them that work for TLDs and to be honest the opinion that I've heard loud and clear so far is what the heck is clearcable doing.

By far the easiest way to fix this would be for clearcable to shorten the RRSET reply by using the various methods that jabley highlighted above.

While I'm not against "fixing" this in the spirit of being nice. This issue is only specific to using certain ATAs on the clearcable service.
--
TSI Gabe - TekSavvy Solutions Inc.
Authorized TSI employee ( »TekSavvy FAQ »Official support in the forum )

mlord

join:2006-11-05
Nepean, ON
kudos:13
+1

34764170

join:2007-09-06
Etobicoke, ON
reply to TSI Gabe
*sad Mac face* kinda disappointed to see TSI's resolvers failing OARC's DNS reply size test.

Boo Google and OpenDNS.

TSI
$ dig @206.248.154.22 +short rs.dns-oarc.net txt
rst.x1002.rs.dns-oarc.net.
rst.x1007.rs.dns-oarc.net.
rst.x1012.rs.dns-oarc.net.
rst.x1257.x1012.rs.dns-oarc.net.
rst.x1228.x1012.rs.dns-oarc.net.

Level 3
$ dig @4.2.2.2 +short rs.dns-oarc.net txt
rst.x3827.rs.dns-oarc.net.
rst.x3837.x3827.rs.dns-oarc.net.
rst.x3843.x3837.x3827.rs.dns-oarc.net.
"192.221.139.217 DNS reply size limit is at least 3843"
"192.221.139.217 sent EDNS buffer size 4096"
"Tested at 2012-10-22 21:01:17 UTC"

home; dnsmasq -> BIND 9.9 (DNS64) -> my Unbound recursive resolver
$ dig @192.168.3.2 +short rs.dns-oarc.net txt
rst.x3827.rs.dns-oarc.net.
rst.x4049.x3827.rs.dns-oarc.net.
rst.x4055.x4049.x3827.rs.dns-oarc.net.
"2001:470:1d:8c::13 DNS reply size limit is at least 4055"
"Tested at 2012-10-22 21:01:58 UTC"
"2001:470:1d:8c::13 sent EDNS buffer size 4096"

34764170

join:2007-09-06
Etobicoke, ON
reply to mlord
said by mlord:

Callcentric.com needs to do better.

No, they don't. It's BYOD. You are responsible if you want to bring broken equipment to their service. If you want to use broken crap then you can support it.