IP traffic over ICMP tunneling
github.com
github.com
I suspect it hasn't gotten a lot of widespread publication in English forums because it's from a University project from Japan so there aren't a lot of English-speaking contributors (there are only 9 contributors to the official repo).
Additionally, it was only open sourced in 2014 so as an open source project it's pretty young.
I remember reading that there was a 10-year agreement that finally ended at the start of 2014, allowing the original developer to go open source. The source tree is different from PacketIX's though, so some of the features are still not available yet in the open source version.
I to was concerned with the legitimacy of the software. But it is open source now, which should aid discovery.
I don't use it anymore at the moment. But my gut feeling is it is legit software, but sometimes there is just no way to know...
My only gripe was user management. It lacks an LDAP or PAM integration, substituting RADIUS instead. No biggy, I can set up a SoftEther->RADIUS->LDAP bridge. The caveat is that SoftEther will only apply RADIUS authentication to accounts you manually define; so you must create a user in SoftEther and enable RADIUS for them. This may have been fixed by now, but was rather annoying back then!
Any captive portal these days block also ICMP.
Most firewalls block ICMP these days, because the days of blacklisting are over and ICMP is not the one who is getting white listed. Why?
The only way these days is to misuse DNS. But even that works less and less reliable.
Also ptunnel comes standard with some linux distro's these days Ubuntu and so do probably most of it's derivatives, and as far as raw performance goes ptunnel is also the highest performing one capable of achieving about 150kbps which isn't that bad considering the sheer amount of packets and overhead you get.
http://manpages.ubuntu.com/manpages/gutsy/man8/ptunnel.8.htm...
What's your question? Is it "What's the point of blocking ICMP?"? Or is it the opposite question?
If it's the former, then there are sysadmins out there who cargo-cult their network configuration and listen to folks like Gibson Research Corporation who've been giving really bad advice [0] for the past decade+.
[0] Specifically, they strongly recommend dropping all traffic to ports that don't have listening services, along with all ICMP, rather than rejecting said traffic and allowing all non-problematic ICMP. They also have a "handy" tool [1] to make it look like doing anything else is "DANGEROUS": (The tool reports [2] if your site responds to ICMP echo requests.)
[1] https://www.grc.com/shieldsup
[2] Ping Reply: RECEIVED (FAILED) — Your system REPLIED to our Ping (ICMP Echo) requests, making it visible on the Internet. Most personal firewalls can be configured to block, drop, and ignore such ping requests in order to better hide systems from hackers. This is highly recommended since "Ping" is among the oldest and most common methods used to locate systems prior to further exploitation.
How about IP over TCP SYN.
After few days of mobile tethering, I realized I could ask their HTTP proxy to open an HTTPS connection to a server outside the network, but instead of sending HTTPS traffic through the proxy, I could send any traffic - like SSH. With this, I was ultimately able to open an SSH-tunnel to my own shell server running OpenVPN outside their network, which then allowed a (surprisingly stable and fast) access to the internet at wide – via an OpenVPN-tunnel wrapped in an SSH-tunnel pretending to be an HTTPS-tunnel.
I don't recall whether ICMP was allowed out at the BigCorp., but I am pretty sure someone will one day find a tool like this quite useful in a similar situation.. :)
Maybe this is why Microsoft Azure never allowed ICMP travseral through their outer firewall despite frequent request from users....
The Great China Firewall and others need deep packet inspection, heuristics and AI to find tunnels set up that way.
In any case they were probably running something like squid with very basic level 7 filtering, so if something comes on 443 they have no option but to forward it.
Having said that, I'm sure there are other usage for such a tool :).
Although I'm interested in comparison as well :)
DNS also requires you to have a DNS server and a domain, and you'll need something to constantly clear the cache on the local machine otherwise you'll eventually run out of room even if you are going to use the max available DNS record size. If anything in the way will keep your DNS queries in cache then you might be screwed and run out of space very quickly.
If you need internet access ICMP tunnel will be better, bandwidth will be limited but it will be more or less a P2P tunnel, if you need to exfiltrate data without explicitly needing to maintain a bi-directional tunnel DNS is the way to go, will also work in more captive portal restrictive cases than ICMP. Today ICMP is usually utterly blocked DNS sometimes work especially in common cases where the restricted network offers some white listed sites (e.g. airport wifi that allows you to access the airport's site and the local train service but blocks everything else).
In any case DNS tunnel offers you both TCP and UDP tunneling at much higher throughput, I'll take a look at your code when I'll have the time and see how it compares to ptunnel or ICMP shell.
I'm not aware of prioritizing smaller packets on the backbone, sounds like something that would be targeted at small flows (i.e. first N packets in a flow get a priority bump)? More info on that would be appreciated.
Also from a more high level point of view if you think about it the small packets are the most critical ones and they are at least as far as responsiveness goes DNS is limited to 512bytes over UDP, TCP 3-way handshake packets are tiny and those are the packets that need to get to and back from their destination as fast as possible, delays in data transfers means slower speeds, delays of handshakes mean that your application can fail or hang. Other important traffic such as VOIP[0] also uses very small packet sizes for this same reason most critical services need to transfer very little data (per given unit of time) but need to update data as frequently as possible to provide the illusion of real time and to mask the latency, same goes for other things like online/multi-player gaming and so on and on and on. Pretty much if you want your service to be as responsive as possible limit your packet size to the smallest size possible and increase your PPS this will ensure that your packets get quicker to their destination. [0]VOIP Packet Sizes http://www.cisco.com/c/en/us/support/docs/voice/voice-qualit...
The only time you would want to use large packets is pretty much when you can have a buffer, this means that you need to handle less packets per second which lowers CPU consumption (across the entire path) so video streaming and such can use pretty much as large of an MTU as they want unless they start getting fragments.
It absolutely does matter and is quite meaningful. :)
If you set your edge router's Internet-facing MTU to 9k, and the upstream equipment's MTU is smaller than that, then either your packets will be dropped, or PTMU Discovery will try to figure out the MTU of the path. (Better hope everyone along the path is correctly handling ICMP! :) )
> The only time you would want to use large packets is pretty much when you can have a buffer...
Or if you have high-volumes of data to move and want to dramatically increase the data:Ethernet_frame_boilerplate ratio. :)
> Also ... if you think about it the small packets are the most critical ones... [because they need to be dispatched as quickly as possible.]
Yes, but a larger MTU shouldn't affect this. Set whatever socket options are required to get those packets on their way as soon as they're created, and your system shouldn't wait to fill an Ethernet frame before sending that packet.
I can't agree with that statement. If upstream devices support larger than 1500 byte MTU, OR PTMU works correctly, then you are absolutely not going to "kill your network stack". At worst, (in the PMTU discovery phase) you'll see poor performance for a few moments while the MTU for the path is worked out, and then nothing but smooth sailing from then on.
> The point being is that for transferring data especially when responsiveness is important if not paramount utilizing the maximum potential frame size you can push without fragmentation would generally yield a poorer result in real world applications.
I'm not sure what you're saying here. Are you saying:
"If you configure your networking equipment to always wait to fill up a full L2 frame before sending it off, you'll harm perf on latency-sensitive applications."?
If you're not, would you be so kind as to rephrase your statement? I may be particularly dense today. :)
However, if you are, then that statement is pretty obvious. I expect that few people configure their networks to do that. However, I don't see what that has to do with the link's MTU. Just because you have a 9k+ MTU, doesn't mean that you have to transmit 9k of data at a time. :)
It's the de-facto MTU of much of The Internet. Baby Jumbo (MTU >1500 but <9k), Jumbo (MTU ~9k), and Super Jumbo (MTU substantially larger than 9k) frames exist, and are supported by many (but -sadly- not all) Ethernet devices.
Edit:
> Also with how global traffic is managed smaller packets tend to get priority...
Do you have a reliable citation for this? I would expect that core and near-core devices would handle so much traffic, that they all would be using MTUs far higher than 1500 bytes per frame.
I did some tests a while and found that iodine was ~98% of non-tunneled speed when I could access the server directly, since then the traffic is wrapped over huge big TXT queries and it's really efficient.
But the common case for using it is that you can only lookup through a local DNS server, and then it's usually ~0.5% or so of the usual speed. I.e. 1-2KB/s at best.
It was pretty much usable circa 2008...
btw, in debian (and probably, derivatives), it is just apt-get away from being installed.
Is there anyway to stop things like this at the corporate firewall?
So you're going to have to do a little bit more configuration than just allow a maximum packet size if you're going to allow ICMP to transit at all you should also limit the allowed set of addresses (you should do that regardless, but echo can be used for amplification requests by virtue of the broadcast feature of the IP protocol). Hence the 'one step away'.
This was known as the 'smurf' attack. Fortunately this is now mostly a thing of the past. But poking holes in your firewall for ICMP is a delicate affair.
# iptables -A FORWARD -p icmp --icmp-type echo-request -m length --length 86:0xffff -j DROP
Update: as for the number of packets, there is -m limit and other recipes.
Also, instead of using the plain limit match, check out hashlimit. It can apply a rate limit on a per sender, destination, or sender+destination basis. The recent match may also be of interest.
Big corporate places can completely restrict things and prevent any traffic from internal hosts to the internet. You can use proxying for web browsing etc. and then monitor that to check for any unauthorised traffic.
Edited for spelling