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Q's about Reverse DNS on my PN address

fishrow
Grafter
Posts: 67
Registered: 31-08-2009

Q's about Reverse DNS on my PN address

Using Gibson's site grc.com with its 'Shields Up' for quick check of firewalls etc.
When you get the start page for the ShieldsUp it obviously shows your internet IP address but it then has a section about Reverse DNS on that address.
Sometimes I will see - "your address has no Reverse DNS". And the text further says this can be good as you can't be easily tracked.
Other times, it will show what the Reverse DNS is, like:
xxx.xxx.xxx.xxx.dyn.plusdsl.net
the x's being what my IP address is.
However, these are the questions:
I have seen this:
xxx.xxx.xxx.xxx.adsl.brightview.com

1.  Why would there be a "brightview" showing?
2. I see from thinkbroadband.com that there is a "brightview" mentioned under the ISP Madasafish. Is there some er, hook that's part of the BT/Plusnet umbrella that's routing me somehow via them?
3. I can't see where any attributes of the router firewall or the different dynamic address I get have any effect on times I see the "no reverse DNS", why or what would cause this to happen?
11 REPLIES
Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: 18-07-2007

Re: Q's about Reverse DNS on my PN address

Hi fishrow,
We bought Madasafish a few years back, then when BT bought us they acquired both. The reason you're getting Brightview on an rDNS lookup is that we've moved some of the BV IP addresses into the Plusnet dynamic pools - it doesn't affect anything other than the rDNS though, and is nothing to worry about.
Hope that clears things up for you.
itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: Q's about Reverse DNS on my PN address

Quote from: fishrow
Sometimes I will see - "your address has no Reverse DNS". And the text further says this can be good as you can't be easily tracked.
Other times, it will show what the Reverse DNS is, like:
xxx.xxx.xxx.xxx.dyn.plusdsl.net

Think it's a bit immaterial on tracking whether there is a reverse DNS or not. All IP's are allocated and it's a simple lookup to find the ISP so can't see any difference having a rDNS of xxx.xxx.xxx.xxx.dyn.plusdsl.net or knowing an IP of xxx.xxx.xxx.xxx is issued to Plusnet.
fishrow
Grafter
Posts: 67
Registered: 31-08-2009

Re: Q's about Reverse DNS on my PN address

To Matt,
ah ok, I see, thanks.  It's more curiosity than 'concern' Smiley

If anyone else can shed light on why the ReverseDNS gives _no_ detail sometimes, I'd appreciate it.
Community Veteran
Posts: 1,101
Registered: 10-09-2010

Re: Q's about Reverse DNS on my PN address

All having no rDNS details means is that Plusnet have not setup rDNS for all their IP addesses, nothing special.
As for GRC saying it makes you less traceable, I don't get that at all, for dynamic IP all it tells anyone is who your ISP is, but thats available directly from the IP anyway, and if you have fixed IP who needs to track you via your ISP, your always going to be on the same IP anyway... so me, right now the GRC statement makes no sense.
fishrow
Grafter
Posts: 67
Registered: 31-08-2009

Re: Q's about Reverse DNS on my PN address

fourfour
ok, so it's a technical facility at the PN end where not all its block of available dynamic IPs can give rDNS info.
I won't pursue the details of that facility but I recollect that I've seen  the info/no-info rDNS with other ISPs . Intriguingly, it would show either over some days even with a static IP.
MJN
Aspiring Pro
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Registered: 26-08-2010

Re: Q's about Reverse DNS on my PN address

Quote from: itsme
Think it's a bit immaterial on tracking whether there is a reverse DNS or not. All IP's are allocated and it's a simple lookup to find the ISP so can't see any difference having a rDNS of xxx.xxx.xxx.xxx.dyn.plusdsl.net or knowing an IP of xxx.xxx.xxx.xxx is issued to Plusnet.

It's not so much the fact that the rDNS exists, but rather that the content of it might give more away than simply knowing what ISP it comes from. For example, it could (and often does) contain geographic information or other identifiers that one might not wish to be so publically announced or that could otherwise aid tracking and tracability.
Mathew
itsme
Grafter
Posts: 5,924
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Registered: 07-04-2007

Re: Q's about Reverse DNS on my PN address

ISP's will not spend time uniquely identifying IP's. The standard format is xxx.xxx.xxx.xxx ISP identifier. I have never seen any with geographic information and if they do exist it will be for the ISP and not of the user that it has been issue to.
From a rDNS of my PN IP address my name, address and telephone number can easily be found.  Cool   
MJN
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Re: Q's about Reverse DNS on my PN address

Quote from: itsme
I have never seen any with geographic information and if they do exist it will be for the ISP and not of the user that it has been issue to.

Virgin Media do (or did) for their cable customers by means of including (at least) UBR location information in the rDNS, information which has a direct correlation to the customer base locations (by area, we're not talking house number and street here). For example, here's an example pulled off a Google search for one customer's rDNS:
cpc2-hawk7-0-0-cust247.aztw.cable.virginmedia.com
I, and no doubt others, happen to know that 'aztw' means Aztec West which is in North Bristol hence that it where the customer is located (or near). Other suburbs of Bristol will be served by different UBRs thus will contain differing geographic identifiers. The 'cpc2-hawk7-0-0-cust24' may well not be giving anything away, or is it? That's GRC's whole point - what might look like gibberish to one person could be very useful tracking information for another. Often it's not the individual nuggets of such information that is an issue but rather the aggregate of multiple bits that can be cause for concern.
Mathew
[Edit: Googling further it seems that Aztec West is the location of the core router, and that 'hawk' is an even more local identifier of which UBR (not sure which - my Bristol geography is not the best!) the customer hangs off (and lives near!)]
itsme
Grafter
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Re: Q's about Reverse DNS on my PN address

Did not realise that but then I have had no dealing with cable. But for them to do that they must be using static (same) IP addresses for each user. One reason that I have not look into going cable was I thought that the only offer dynamic IP's As I run servers I prefer static and also control over the rDNS. 
MJN
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Re: Q's about Reverse DNS on my PN address

Quote from: itsme
Did not realise that but then I have had no dealing with cable. But for them to do that they must be using static (same) IP addresses for each user. One reason that I have not look into going cable was I thought that the only offer dynamic IP's As I run servers I prefer static and also control over the rDNS.

At the risk of drifting off-topic, whilst the assignments on VM's cable network are dynamic they are actually very static in everything but name! It is not uncommon for customers to remain on the same address for months if not years - you would only lose your address if you turned your modem off for a fair amount of time (hours, perhaps even 24), long enough for another customer to jump in an grab it. That, or if VM reconfigured their network and/or address pool and booted everyone off at the same time.
My move from cable to ADSL was a bit of an eye-opener for me - I evidently didn't really know (or rather appreciate) quite how dynamic a dynamic allocation could really be! My dynamic DNS scripts have never been worked so hard! Wink
A lot probably boils down to the differences in how cable networks function compared against ADSL and that the edges of the core network are much closer to the end user (e.g. on ADSL the aggregation point for all customers may well be the exchange, however on cable the aggregation point could well be the box at the end of the road or a UBR serving only a small area). Thus, any means of network identification could, quite literally, be much closer to home.
Cable/ADSL differences aside, I'm sure there must be some ISPs out there who might give you a static IP with a default rDNS along the lines of mrjohnsmith.wirral.northwest.staticcustomers.noclueISP.com because, for whatever reason, it seemed to make sense at the time....
Mathew
itsme
Grafter
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Registered: 07-04-2007

Re: Q's about Reverse DNS on my PN address

I believe with PN and their static allocation it's username.plus.net. But it's so long ago when I had a default rDNS as PN allow you to change it.