8 ms·

A really shady ISP could intercept and redirect any outgoing port 53 traffic to their servers.

by helfire 13y ago

dmourati 13y ago
If that were the case, I would immediately terminate any relationship with them and out them in public. While technically possible, you're now talking about a whole other form of dishonest behavior. Some would say criminal.
- anonymoushn 13y ago
  This has been done. I'm not sure how prevalent it is now. http://comcastisfuckingwithyourport53traffic.wordpress.com/ http://comcastisfuckingwithyourport53traffic.wordpress.com/
cdjk 13y ago
That's what my ISP does. What's worse is that sometimes their dns servers fail intermittently (something to do with fragmented packets and retrying DNS queries in TCP mode). It did take a while to figure out what was causing the intermittent DNS failures. "My ISP is hijacking all port 53 traffic" was fairly low on my list of possibilities, I must admit. Fortunately it's not that hard to run a local resolver that forwards queries to an external resolver on a vps on an alternate port. I'd switch ISPs, but I live in a remote area and my only other choices would be satellite or cellular, so I'm stuck with them.
aendruk 13y ago
My ISP [1] actually does this. They offer an opt-out of NXDOMAIN hijacking, but silently proxy all port 53 traffic regardless. This experience has taught me simply to distrust the DNS protocol in its current form and use DNSCrypt in all situations. [1]: Shaw Communications, chosen by the landlord. [2]: http://dnscrypt.org/
- mhurron 13y ago
  Are you using Shaw's DNS servers? I don't remember dealing with NXDOMAIN issues when I had Shaw, but I have run my own DNS servers for a long time now. It's been 7 years or so since I used Shaw.
  - aendruk 13y ago
    It doesn't matter what DNS servers I specify; Shaw intercepts all DNS requests. I can even make up a nonexistent DNS server as long as it's internet-routable, and will get a valid response from Shaw. This works, for example: dig @www.facebook.com news.ycombinator.com
    - gwu78 13y ago
      All that means is that you're using their recursive DNS servers. They can configure these any way they choose. Stop using third party recursive DNS servers and you will not have problems with unwanted advertising and NXDOMAIN hijacking. Run your own recurive DNS server (e.g. dnscache) on 127.0.0.1. Alternatively, query authoritative servers directly. Use a port other than 53 if you really think your ISP is trying to filter your outgoing queries; I sincerely doubt they would bother. 192.5.6.30 is an authoritative .com server. Memorize that number. dig +norecurse -b0.0.0.0#5353 news.ycombinator.com @192.5.6.30 The names on the right of the "NS" rows are the authoritative servers for ycombinator.com. (Cloudflare. No comment.) 192.5.6.30 has the IP addresses for those. You'll find them in the "ADDITIONAL SECTION". Let's say it lists 1.2.3.4 as an IP address. dig +norecurse -b0.0.0.0#5353 news.ycombinator.com @1.2.3.4 And you should receive the IP address for news.ycombinator.com, or at least your next clue where to look (if the DNS admin has chosen to play games with CNAME). This method can be automated. Your ISP is not "intercept[ing] all DNS requests". You are sending your requests to your ISP's recursive DNS servers (why?), and those servers are feeding you whatever information the ISP chooses. Go figure, they are sending you bogus info to inject advertising. Solution: Stop sending your requests to your ISP's recursive DNS servers (or any third party recursive DNS servers). Send your requests to your own recursive DNS server running on 127.0.0.1, or send nonrecursive requests to authoritative DNS servers only.
      - 13y ago
- mike-cardwell 13y ago
  DNSCrypt is useless. Yeah, they can't see that you did a DNS A record lookup for www.example.com, but they can still see your subsequent TCP connection to the IP you received in your encrypted DNS response, and see the HTTP Host header that your browser sends. Even if it's a HTTPS connection, modern browsers leak the hostname then too, due to SNI. Signing DNS responses has much more value than encrypting them. If you set up DNSCrypt with OpenDNS, you're not improving the situation. You're just adding an additional third party that can see what you're doing.
  - ars_technician 13y ago
    Why do you keep posting this? It's irrelevant because the idea isn't to hide what site you're visiting, it's to prevent the ISP from modifying the DNS responses. Signing DNS responses would be helpful if that was actually enforced anywhere. DNSCrypt is a perfectly fine solution for this threat model.
    - mike-cardwell 13y ago
      "Why do you keep posting this?" I posted a similar comment twice in response to different people. There is nothing wrong with this. The rest of your comment is irrelevant as it assumes I'm replying to the article rather than to the parent comment. The parent stated that he uses "DNSCrypt in all situations." I don't want people to think this is a good idea.

A really shady ISP could intercept and redirect any outgoing port 53 traffic to their servers.

by helfire 13y ago

A really shady ISP could intercept and redirect any outgoing port 53 traffic to their servers.

If that were the case, I would immediately terminate any relationship with them and out them in public. While technically possible, you're now talking about a whole other form of dishonest behavior. Some would say criminal.

anonymoushn 13y ago
This has been done. I'm not sure how prevalent it is now. http://comcastisfuckingwithyourport53traffic.wordpress.com/ http://comcastisfuckingwithyourport53traffic.wordpress.com/

cdjk 13y ago

That's what my ISP does. What's worse is that sometimes their dns servers fail intermittently (something to do with fragmented packets and retrying DNS queries in TCP mode). It did take a while to figure out what was causing the intermittent DNS failures. "My ISP is hijacking all port 53 traffic" was fairly low on my list of possibilities, I must admit. Fortunately it's not that hard to run a local resolver that forwards queries to an external resolver on a vps on an alternate port. I'd switch ISPs, but I live in a remote area and my only other choices would be satellite or cellular, so I'm stuck with them.

aendruk 13y ago

My ISP [1] actually does this. They offer an opt-out of NXDOMAIN hijacking, but silently proxy all port 53 traffic regardless. This experience has taught me simply to distrust the DNS protocol in its current form and use DNSCrypt in all situations. [1]: Shaw Communications, chosen by the landlord. [2]: http://dnscrypt.org/

mhurron 13y ago
Are you using Shaw's DNS servers? I don't remember dealing with NXDOMAIN issues when I had Shaw, but I have run my own DNS servers for a long time now. It's been 7 years or so since I used Shaw.
- aendruk 13y ago
  It doesn't matter what DNS servers I specify; Shaw intercepts all DNS requests. I can even make up a nonexistent DNS server as long as it's internet-routable, and will get a valid response from Shaw. This works, for example: dig @www.facebook.com news.ycombinator.com
  - gwu78 13y ago
    All that means is that you're using their recursive DNS servers. They can configure these any way they choose. Stop using third party recursive DNS servers and you will not have problems with unwanted advertising and NXDOMAIN hijacking. Run your own recurive DNS server (e.g. dnscache) on 127.0.0.1. Alternatively, query authoritative servers directly. Use a port other than 53 if you really think your ISP is trying to filter your outgoing queries; I sincerely doubt they would bother. 192.5.6.30 is an authoritative .com server. Memorize that number. dig +norecurse -b0.0.0.0#5353 news.ycombinator.com @192.5.6.30 The names on the right of the "NS" rows are the authoritative servers for ycombinator.com. (Cloudflare. No comment.) 192.5.6.30 has the IP addresses for those. You'll find them in the "ADDITIONAL SECTION". Let's say it lists 1.2.3.4 as an IP address. dig +norecurse -b0.0.0.0#5353 news.ycombinator.com @1.2.3.4 And you should receive the IP address for news.ycombinator.com, or at least your next clue where to look (if the DNS admin has chosen to play games with CNAME). This method can be automated. Your ISP is not "intercept[ing] all DNS requests". You are sending your requests to your ISP's recursive DNS servers (why?), and those servers are feeding you whatever information the ISP chooses. Go figure, they are sending you bogus info to inject advertising. Solution: Stop sending your requests to your ISP's recursive DNS servers (or any third party recursive DNS servers). Send your requests to your own recursive DNS server running on 127.0.0.1, or send nonrecursive requests to authoritative DNS servers only.
    - 13y ago
mike-cardwell 13y ago
DNSCrypt is useless. Yeah, they can't see that you did a DNS A record lookup for www.example.com, but they can still see your subsequent TCP connection to the IP you received in your encrypted DNS response, and see the HTTP Host header that your browser sends. Even if it's a HTTPS connection, modern browsers leak the hostname then too, due to SNI. Signing DNS responses has much more value than encrypting them. If you set up DNSCrypt with OpenDNS, you're not improving the situation. You're just adding an additional third party that can see what you're doing.
- ars_technician 13y ago
  Why do you keep posting this? It's irrelevant because the idea isn't to hide what site you're visiting, it's to prevent the ISP from modifying the DNS responses. Signing DNS responses would be helpful if that was actually enforced anywhere. DNSCrypt is a perfectly fine solution for this threat model.
  - mike-cardwell 13y ago
    "Why do you keep posting this?" I posted a similar comment twice in response to different people. There is nothing wrong with this. The rest of your comment is irrelevant as it assumes I'm replying to the article rather than to the parent comment. The parent stated that he uses "DNSCrypt in all situations." I don't want people to think this is a good idea.