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Mick <michaelkintzios@×××××.com> [15-08-01 12:20]: |
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> On Saturday 01 Aug 2015 10:48:15 Alan McKinnon wrote: |
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> > On 01/08/2015 11:21, Meino.Cramer@×××.de wrote: |
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> > > Hi, |
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> > > |
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> > > With ufw I want temporary block any access from my Gentoo PC to certain |
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> > > domains. Since domain names change IP addresses I dont want to block |
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> > > on base of the IP only. |
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> > > |
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> > > Is this possible with ufw? |
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> > |
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> > That is really not a good idea, which is why packet filtering firewalls |
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> > seldom attempt it. |
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> > |
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> > It means that *every*single*packet* involves a reverse DNS lookup to get |
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> > the (unreliable) DNS name (which might not even be listed at all), do a |
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> > string comparison and make a block decision based on that. All of which |
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> > is probably an order of magnitude more resource use that simply sending |
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> > the packet out. There are optimizations of course, such as caching the |
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> > results of previous lookups, but there's still a considerable overhead. |
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> > |
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> > There's a few ways around it: |
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> > |
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> > 1. Rethink your firewalling policy. Maybe you really don't need to block |
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> > stuff and just think you do. |
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> > |
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> > 2. Do a DNS lookup and check the TTL. If it's high, say 86400 then it |
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> > cannot change more than once a day. So you only need to do a lookup once |
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> > a day. Write or get a script that looks up your banned domains every so |
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> > often, gets the new IP if it changed and reload a new netfilter rule set. |
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> > |
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> > #2 is the correct approach for large firewalls with many users but does |
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> > involves a quite sophisticated codebase, probably way more than you need |
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> > for your 1 pc. Which brings us back to #1 |
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> |
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> There's also the option to set in /etc/hosts: |
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> |
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> 127.0.0.1 safebrowsing.clients.google.com |
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> |
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> (Replace the google domain above with whatever you want to stop access to). |
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> |
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> -- |
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> Regards, |
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> Mick |
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|
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Hi Mick, |
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|
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yes this comes close to what I want, but it is not that easy to switch |
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on/off. |
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|
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Background: |
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I have a Android tablet which I connected via Wifi to my PC and |
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started wireshark before the connection was etablished. |
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|
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As soon the connection was there, the tablet starts to phone home. |
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I want to stop that for the case, when the tablet accesses those |
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domains, since in that case an tablet ID or whatever this |
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"anonymous identification" is called is transmitted. |
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|
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Next came iptables into my mind since it is a configuration |
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item and not a phyical thing like a file. |
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|
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Is there a way (for example via something below /proc or /sys) to |
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feed the contents of /etc/hosts into the kernel instead of using |
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the physical file? |
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|
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Best regards |
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Meino |
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