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mlord

join:2006-11-05
Nepean, ON
kudos:13
reply to neko

Re: Google DNS versus ours

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 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.


TSI Marc
Premium,VIP
join:2006-06-23
Chatham, ON
kudos:28
reply to TSI Gabe
Gabe, what I don't understand is how come they're not signing up for our TekTalk service?
--
Marc - CEO/TekSavvy

wally_walrus

join:2009-10-07
Orleans, ON
Marc,

When your prices and service are going to match Callcentric's I'll switch in an instant


TSI Marc
Premium,VIP
join:2006-06-23
Chatham, ON
kudos:28
What are you paying with them?
--
Marc - CEO/TekSavvy

wally_walrus

join:2009-10-07
Orleans, ON
All PAYG for the last month:

Total: 289 min 0 min 141 min $5.5818 $0.0000 $5.5818


TSI Marc
Premium,VIP
join:2006-06-23
Chatham, ON
kudos:28
What package are you getting from them?
--
Marc - CEO/TekSavvy

wally_walrus

join:2009-10-07
Orleans, ON

1 edit
No package at all - I pay by the minute (only for what I use), and - BEST THING - the balance never expires

Their rates are at callcentric.com


neko
All Hail Canada
Premium
join:2006-08-11
Canada
Reviews:
·TekSavvy Cable
reply to TSI Marc
I'm on PAYG, too. About $5 every month.

Their back-end portal is fantastic with the call filtering options to prevent spam, re-route calls, free incoming/outgoing SIP, free voicemail. The list of features is outstanding.

My favorite feature is the call filtering. They even support wilcard numbers which add a granularity to the service that I find very useful.

They are rated as the best VOIP provider on DSLR.
--
...virtue gives you heraldry.

OTIS3

join:2011-09-29
reply to TSI Marc
I'm also on the pay as you go with CallCentric. I pay $1.95 for my DID, $1.50 for E911, and most calling is about $0.015 per minute. Most months costs me about $5. I prepay with paypal on my account usually $50 and lasts at least a year, so its also one more bill I dont have to think about. They will send me an email when the balance in my account is low.

Also, as others have mentioned, the customer portal is really good. The amount of options is great. Rarely do I get telemarketers or credit cards scams calling, but if they do, its only 30 seconds to add them to a block list.


rodjames
Premium
join:2010-06-19
Gloucester, ON
reply to neko
Their website is lacking any functionality, products or ordering. They also have multiple 404 errors on their site. Not very promising at this point. Even though it's only 5$ they should still try and sell their product a bit better.


neko
All Hail Canada
Premium
join:2006-08-11
Canada
Perhaps the problem is on your end, as their website is fully functional for me, & I assume others.
--
...virtue gives you heraldry.

Guru

join:2008-10-01
kudos:2
So this thread has turned from DNS to VOIP now?

** Their website works perfectly fine for me too!


Kev
TekSavvy.com
Premium
join:2005-06-12
canada
Reviews:
·TekSavvy Cable
reply to OTIS3
said by OTIS3:

I'm also on the pay as you go with CallCentric. I pay $1.95 for my DID, $1.50 for E911, and most calling is about $0.015 per minute. Most months costs me about $5. I prepay with paypal on my account usually $50 and lasts at least a year, so its also one more bill I dont have to think about. They will send me an email when the balance in my account is low.

Also, as others have mentioned, the customer portal is really good. The amount of options is great. Rarely do I get telemarketers or credit cards scams calling, but if they do, its only 30 seconds to add them to a block list.

I'm paying $30 per year on Nettalk... unlimited Canada and US including all 911 and voice record services, caller ID.. etc...
--
Teksavvy.com + 300GB Bandwidth awesomeness!