Subject: Internet Gateway Search
This text describes a change to the Npv7. It will be included in the final documentation, so feel free to correct it. But if you want to change the system here described, please contact us first.
If the nodes are in restricted mode (compatibility with the Internet), they should share their Internet connection. This can be easily done, in fact, if a node X, connected to the Internet, activates the masquerading, it is possible for the other nodes to connect by setting as the default gateway their rnode which lead to the node X.
This can be automated by Netsukuku itself and it requires small changes in the code: it is just necessary that the nodes connected to the Internet set a flag in the qspn_pkt, in this way the other nodes will know the routes to reach the Internet.
The situation becomes a little complex when there is more than one node which shares its internet connection. Let's consider this scenario:
A(gw) B(gw) \ / \___ ___/ \/ Ntk nodes (10.x.x.x)
A and B are nodes which shares their internet connection, we call them gateways. Let's call X the node which wants to connect to an Internet host. In this case, the nodes near A, might find useful to use A itself to reach the Internet, the same happens for the nodes near B. Instead, the nodes in the middle don't know what is the best choice and they might continuosly change their gw. This means that a TCP connection (to an inet host), which was established trough A, when is then routed trough B dies because A and B have different public IPs on the Internet.
The node X has to create an IPIP tunnel to the gateway it wants to use, and set as default gw the tunnel. In this way, the node X is sure to always use the same gateway while the routing of the packets between it and the gw is made transparently by the other Netsukuku nodes.
Anti loop multi-inet_gw shield
An inet-gw is a normal node like all the other, therefore it can use the Internet connections of the other inet-gws in conjunction with its own one.
Consider the previous scenario, A and B are two inet-gw. A sets in his internet default route the ADSL modem and B. B does the same, but sets A as the second default route.
What would happen if the default route, written in the routing cache of A, is B and, at the same time, the default route set in the routing cache of B is A? The packets would jump endlessly in a infinite loop loosing themselves forever.
That's why we need the "anti loop multi-inet_gw shield". Its working way is simple: each inet-gw has a netfilter rule which marks all the packets coming from the outside and directed to the Internet. These packets are then routed directly to the Internet without being sent, again, to an inet-gw. In the example: A wants to send a packet to the Internet and it looks in its routing cache. It decides to forward the packet to B. B receives the packet, recognizes it is an external packet directed to the Internet and shoots it on its modem.
Let's consider the previous scenario.
The node X can also decide to use both A and B to reach the Internet, using at the same time their connections! Even the gw A can use at the same time its own line and the connection of the gw B.
The procedure to implement this is what follows:
- X creates a tunnel to A and another one to B
- X adds in the routing table the default route using A and B as multipath
gateways. The gateway for the connections is chosen randomly.
- X adds a rule in the routing table to route all the packets of established
connections trough the same gateway used to create the same connection. The rule is linked to some netfilter rules which track and mark each connection. The method is described in details here: https://lists.netfilter.org/pipermail/netfilter/2006-March/065005.html
The implementation of the Load sharing is very Linux specific, so it will be very difficult to port it to other kernels, therefore this feature will be available only to nodes which run Linux (ehi, one more reason to use Linux ;).
Each node sharing the Internet connection (inet-gw) has to masquerade its interfaces, so iptables must be used. In order to keep the daemon portable, NetsukukuD will launch the script found at /etc/netsukuku/masquerade.sh, which in Linux will be a simple script that executes "iptables -A POSTROUTING -t nat -j MASQUERADE". When NetsukukuD is closed the added firewall rules are flushed with "/etc/netsukuku/masquerade.sh close"
The inet-gw can also shape its internet connection in order to prioritize its local outgoing traffic (the traffic coming from its 192.168.x.x LAN). In this way, even if it shares its Internet connection, it won't notice any difference 'cause it will have the first priority. Moreover with the traffic shaper, the inet-gw can also prioritize some protocol, i.e. SSH.
The traffic shaper will activated at the start of NetsukukuD. The daemon will run the /etc/netsukuku/tc_shaper.sh script, which in Linux utilizes the iproute2 userspace utility. When the daemon is closed the traffic shaping will be disabled with "/etc/netsukuku/tc_shaper.sh close".
For more information on the necessity of using ipip tunnels in an adhoc network used to share internet connections, you can read this paper: http://www.olsr.org/docs/XA-OLSR-paper-for-ICC04.pdf