I have a router running Linux that acts as the central gateway to the Internet for a network of embedded devices that use IPv6 to communicate. I would like to intercept, inspect, and rewrite every packet that goes in and out from the Internet to this subnetwork. The reason I need to do this is that I want to create a transparent (to both ends) proxy service that will redirect packets, ingoing and outgoing, to a cache that lives elsewhere depending on the packet content.
These devices communicate using their own application protocol that runs over UDP so I can't re-use something like Squid straight out of the box. Is the best place to start somewhere like libpcap? Or should I start from the top and rewrite Squid? This is the first time I've had to really dive deep into networking, and I'm unsure where to begin.
You are probably better off rewriting the DNS responses to point to your Linux gateway instead. Something similar to this has been done to allow IPv6 only nodes to talk to the IPv4 internet. You can inspire yourself from that.
See for ideas for your Linux gateway box
http://www.ietf.org/id/draft-ietf-behave-v6v4-xlate-stateful-08.txt
and ideas for your DNS box
http://www.ietf.org/id/draft-ietf-behave-dns64-06.txt
Related
I'm new to proxies and Squid so please bear with me.
I'm trying to make a quick and dirty proxy out of my raspi. I've got it set up so I can block certain websites/domains, but I need to be able to block outbound traffic to specific port ranges for specific IP ranges.
Is this even possible? Everything I've found so far is about blocking traffic from certain IP's and ports on your home network.
Edit: This is only going to be used by a few devices on my network, so there shouldn't be too much trouble with bottlenecks.
I'm wondering whether it's technically possible to detect IPv6 clients that are on my website?
I'm currently running Classic ASP using Request.ServerVariables("remote_addr") to detect my visitors IP addresses but some of my mobile users (which I think are Telstra customers here in Australia) are now using IPv6. This function only seems to give me an IPv4 address.
Is there an easy/free solution to detect IPv6 addresses of my visitors?
PS - I don't believe IPv6 is enabled on the server, so am I wasting my time?
Your website can only be reached over IPv6 if your webserver and ISP support it. When your server doesn't have IPv6 there is usually a translation mechanism in the user's ISP's network (NAT64) that translates the user's IPv6 packets to IPv4 packets that can reach your server. Because of that you will only see IPv4 connections coming in. Some of those will be real IPv4 users, some will be IPv6 users that got translated into IPv4.
If you want to be optimally reachable for all users then relying on someone else's translation mechanism is a hack that you'd want to avoid. Asking your ISP/hoster/sysadmin/etc to make your server reachable over IPv6 as well as over IPv4 is the best solution. That way all users can directly contact your server, no matter what their ISP offers.
If the clients are IPv6-only and do not have access to any transition mechanism they will never be able to reach your IPv4-only service in the first place.
In that case it will appear to those users as if your server is down and you will have no way of knowing they even tried reaching your server.
However IPv6-only clients with no access to a transition mechanism are still very rare. More likely the clients will have access to some transition mechanism such as NAT64.
There are a few ways to know if a client accessed your site through a NAT64.
The IPv4 address of the NAT64 may have information in reverse DNS or whois which will tell you that it is a NAT64 device. Additionally clients relying on NAT64 will often be unable to access literal IPv4 addresses. Only access through hostnames work as they rely on DNS64 to find the IPv6 address.
Another way of telling the difference is that the MSS value advertised in SYN packets tend to have different values for native IPv4 clients and NAT64 translated clients.
None of these are 100% reliable ways of telling the difference, but as long as the clients don't have any incentive to mess with your results they can provide a good estimate.
Notice that though the DNS64/NAT64 combo will allow IPv6-only clients to access IPv4-only servers it will not work with servers that have bad or misconfigured IPv6 access. So before you add an AAAA record on your domain make sure that the IPv6 address actually works. And once you have set up the AAAA record you can use a service such as https://nat64check.org/ to verify that it actually works.
Appreciate both responses above, it's made things significantly clearer for me.
After some further reading/investigation, it's apparent that IPv6 packets are being translated to IPv4 (or they are dual-stacking). If the former, I'm now trying to see if I can convert them at my end.
One example is this IPv6 address: 2001:8003:1909:2700:3c97:38e7:9c98:bb5b
It's being translated to IPv4 as: 101.177.229.36
There are many online calculators but none seem to give me the above conversion so I'm thinking their ISP is using their own translation mechanism.
How do I know visitor's MAC address on linux hosting (nginx)?
From ethernet user.
Thanks.
You cannot get that through PHP.
Networks protocol are used in a stack. When doing HTTP communications, your web server uses the HTTP protocol, responsible for the high-level communications. This protocol is implemented on the top of the TCP protocol (which brings stream-like connections and port numbers), which in turn is implemented on the top of the IP protocol (v4 or v6, which bring IP addresses for identification), which in turn is implemented on the top of the Ethernet protocol.
The Ethernet protocol is the one you would need to work with. It has both the source MAC address and the destination MAC address. However, most unfortunately, there are a lot of problems with it.
First, the data it conveys is probably hard to access: I say "probably" because I never stumbled upon how to do it.
Second, much like you get your client's router address when they access your site, you get your client's router MAC address at the Ethernet level. Unless they don't traverse any router (which would only happen if your server was directly wired to your client machine without any router interfering, because there are a whole lot of routers out there that relay data to other parts of the Internet), there is no chance that the MAC address you'll receive will be your client's.
Third, Apache will never try to access that data. And since PHP is "sandboxed" into the network environment Apache gives it, there is no way you can wind back to the Ethernet protocol.
So accessing the MAC address of a visitor from a website, from PHP, is not possible.
EDIT Seems you've taken out the PHP part from your question. So obviously, the last point won't stand anymore.
You can't get that with php it's not included in http
The more general question is this one. Since all PHP has to work with (I'm assuming this is PHP running on your webserver, here) is the HTTP request, you won't be able to get the MAC address. That requires something running on the visitor's side.
This may, or may not work. I know it will work on LAN clients, however for external clients it may be incorrect. I don't overly know my networking, but it's worth a shot right?
If you execute the arp -a command on either windows or linux, it will print out your arp records, which you can then parse for the mac.
Other than that, as far as I know, apache (and therefor php) doesn't just give out mac addresses in its env vars.
*Edited: Sorry, that won't work... The better utility is arping however that will just give you the mac of your router.
If you want to do this, clients will need to be directly connected to your server, with no router in between...
However if that is the case, then arping will work... I don't know of a better tool, but it seems a bit wasteful to do a ping (in root) for just a mac address.
The mac address is only visible on for the network provider if i'm correct (your internet host can see the mac address of your router for example), don't think you can get it with php.
alt text http://img440.imageshack.us/img440/6950/problemyd1.png
(The curly lines with dots represent a network route.)
Having a process called "foo.exe", is there a way to forward everything it communicates over TCP/IP to a forwarding proxy located elsewhere? This forwarding should not reflect to other processes.
Another question: if there are multiple network adapters, is it possible to force a process to use one specific adapter.
Since in this example the targethost.com is known, I could just edit "system32\drivers\etc\hosts" to map targethost.com's IP to localhost, where on port 8765 would be the first forwarder waiting for an incoming connection and pass everything forward to proxy.foo.com. I was wondering if there's a more elegant way of doing this.
This is not for malware, I'm doing some network testing with my complex home network. Thank you for warning us.
Some free software for this would be perfect, alternatively a code idea (native or .net). Thank you very much.
It's not too hard if you make your own computer a firewall, then your app connects to a port on your own computer, and that port is forwarded to both the original destination and logged or forwarded on to your spying computer.
Alternatively you can make your other computer the firwall and have it log/forward the info.
Finally you could use a sniffer.
SocksCap will probably do the job (if you're OK with establishing a SOCKS proxy at proxy.foo.com).
You could hook into the TCP stack, for example, by using the Windows Filtering Platform or its predecessors, or you could substitute the network libraries/calls of that particular process.
Consider the following setup:
A windows PC with a LAN interface and a WiFi interface (the standard for any new laptop). Each of the interfaces might be connected or disconnected from a network. I need a way to determine which one of the adapters is the one connected to the internet - specifically, in case they are both connected to different networks, one with connection to the internet and one without.
My current solution involves using IPHelper's "GetBestInterface" function and supplying it with the IP address "0.0.0.0".
Do you have any other solutions you might suggest to this problem?
Following some of the answers, let me elaborate:
I need this because I have a product that has to choose which adapter to bind to. I have no way of controlling the setup of the network or the host where the product will run and so I need a solution that is as robust as possible, with as few assumptions as possible.
I need to do this in code, since this is part of a product.
#Chris Upchurch: This makes me dependent on google.com being up (usually not a problem) and on any personal firewall that might be installed to allow pinging.
#Till: Like Steve Moon said, relying on the adapter's address is kind of risky because you make a lot of assumptions on the internal network setup.
#Steve Moon: Looking at the routing table sounds like a good idea, but instead of applying the routing logic myself, I am trying to use "GetBestInterface" as described above. I believe what it should do is exactly what you outlined in your answer, but I am not really sure. The reason I'm reluctant to implement my own "routing logic" is that there's a better chance that I'll get it wrong than if I use a library/API written and tested by more "hard-core" network people.
Technically, there is no "connected to the Internet". The real question is, which interface is routeable to a desired address. Right now, you're querying for the "default route" - the one that applies if no specific route to destination exists. But, you're ignoring any specific routes.
Fortunately, for 99.9% of home users, that'll do the trick. They're not likely to have much of a routing table, and GetBestInterface will automatically prefer wired over wireless - so you should be good. Throw in an override option for the .1% of cases you screw up, and call it a day.
But, for corporate use, you should be using GetBestInterface for a specific destination - otherwise, you'll have issues if someone is on the same LAN as your destination (which means you should take the "internal" interface, not the "external") or has a specific route to your destination (my internal network could peer with your destination's network, for instance).
Then again, I'm not sure what you plan to do with this adapter "connected to the Internet", so it might not be a big deal.
Apparently, in Vista there are new interfaces that enable querying for internet connectivity and more. Take a look at the NLM Interfaces and specifically at INetworkConnection - you can specifically query if the network connection has internet connectivity using the GetConnectivity method.
See also: Network Awareness on Windows Vista
Unfortunately, this is only available on Vista, so for XP I'd have to keep my original heuristic.
I'd look at the routing table. Whichever NIC has an 0.0.0.0 route AND is enabled AND has the lowest metric, is the nic that's currently sending packets to the internet.
So in my case, the top one is the 'internet nic'.
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 10.0.0.10 10.0.0.51 20
0.0.0.0 0.0.0.0 10.0.0.10 10.0.0.50 25
(much other stuff deleted)
Another alternative is to ping or GetBestInterface 4.2.2.2 - this is an old and venerable DNS server, currently held by GTEI; formerly by Sprint if I remember right.
Start > Run > cmd.exe (this works in XP and Vista): ipconfig /all
This displays all info about the interfaces in your computer. The "public" facing interface should have a public IP address. For starters, it should not be 192.168.x.x or 10.x.x.x :)
running traceroute to some public site will show you. Of course, there may be more than one interface that would get you there.
Look at the routing table? Generally, unless you're routing between the networks in windows (which is possible, but unusual for a client computer these days) the interface that holds the default route is going to have the Internet connection.
Your question didn't detail why or what you're doing this with so I can't provide any specifics. The command line tool "route" may be of some help, but there are probably libraries for whatever programming language you're using to look at the routing table.
You can't rely on the IP address of the interface (e.g., assuming an RFC-1918 address [192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8] isn't the internet) since most sites have some kind of NATed firewall or proxy setup and the "internet" interface is really on a "private" lan that gets you out to the Internet.
UPDATE: Based on your further information, it sounds like you have a decent solution. I'm not so sure about the choice of 0.0.0.0 since that's a boundary case for IP address -- might be OK on your particular mix of platform/language. Sounds (from the API description) like you could just specify an address, so why not some address known to be on the Internet, e.g. the IP address of your web site, or something more random like 65.66.67.68? Just make sure not to pick one of the rfc-1918 addresses, or the localhost range (127.0.0.0/8), or multicast, any other reserved range, and any address that resolves to a .mil or .gov (while it doesn't sound like getbestinterface sends any traffic, it would suck to find out by having the feds break your door down... :)
Looking at the network point of view, either could be routing to the "internet" at any time. If things like spanning tree protocol are enabled on a switch then you may find that what may have been the routing card to begin with may not be anymore.
Ping google.com though each NIC.