# A Multi-Path Bidirectional Layer 3 Proxy

## Setup Notes
### Linux
#### Policy Based Routing

    ip route flush 10
    ip route add table 10 to 1.1.1.0/24 dev eth1
    ip rule add from 1.1.1.4 table 10 priority 10

    ip route flush 11
    ip route add table 11 to 1.1.1.0/24 dev eth2
    ip rule add from 1.1.1.5 table 11 priority 11

#### ARP Flux

    sysctl -w net.ipv4.conf.all.arp_announce=1
    sysctl -w net.ipv4.conf.all.arp_ignore=1
    
See http://kb.linuxvirtualserver.org/wiki/Using_arp_announce/arp_ignore_to_disable_ARP
    
### Setup Scripts
These are functional setup scripts that make the application run as intended on Linux. They should later be split into
component parts, or incorporated into the main application.

#### Remote Portal

    #!/bin/bash
    set -e
    
    # IPv4 Forwarding
    sysctl -w net.ipv4.ip_forward=1
    
    # Tunnel addr/up
    ip addr add 172.19.152.2/31 dev nc0
    ip link set up nc0
    
    # Deliberately break local routing
    ip rule add from all table local priority 20
    ip rule del 0 || true
    
    # Route packets to the interface but for nc to this host
    ip rule add to 1.1.1.3 dport 1234 table local priority 9
    
    # Route packets to the interface but not for nc via the tunnel
    ip route flush 10
    ip route add table 10 to 1.1.1.3 via 172.19.152.3 dev nc0
    ip rule add to 1.1.1.3 table 10 priority 10
    
#### Local Portal

    #!/bin/bash
    set -e
    
    # Fix ARP
    sysctl -w net.ipv4.conf.all.arp_announce=1
    sysctl -w net.ipv4.conf.all.arp_ignore=1
    
    # IPv4 Forwarding
    sysctl -w net.ipv4.ip_forward=1
    
    # Tunnel addr/up
    ip addr add 172.19.152.3/31 dev nc0
    ip link set up nc0
    
    # Fix routing out of the correct interfaces
    ip route flush 10
    ip route add table 10 to 1.1.1.0/24 dev eth1
    ip rule add from 1.1.1.4 table 10 priority 10
    
    ip route flush 11
    ip route add table 11 to 1.1.1.0/24 dev eth2
    ip rule add from 1.1.1.5 table 11 priority 11
    
    # Route packets from the remote portal's address on the client interface via the tunnel
    ip route flush 12
    ip route add table 12 to 1.1.1.0/24 via 172.19.152.2 dev nc0
    ip rule add from 1.1.1.3 iif eth3 table 12 priority 12
    
    # Route packets to the remote portal's address out of the client interface
    ip route flush 13
    ip route add table 13 to 1.1.1.3 dev eth3
    ip rule add to 1.1.1.3 table 13 priority 13
    
#### Client

No configuration needed. Simply set the IP to that of the remote server/32 with no gateway.