Multiple IP addresses on one NIC and Multiple internet connections on one nic

isp isps nic ip alias ip aliasing multiple ips on one nic

basics

Enable ip forwarding

sysctl net.ipv4.ip_forward

or

echo 1 > /proc/sys/net/ipv4/ip_forward

Multiple Connections to the Internet / two isps on one nic

/etc/shorewall/interfaces

net     eth0    82.94.91.79,188.204.140.224 routeback

/etc/postfix/main.cf

add 188.204.140.192/27 to mynetworks

/etc/iproute2/rt_tables

#
# reserved values
#
255     local
254     main
253     default
0       unspec
#
# local
#
#1      inr.ruhep
82 sdsl
188 fibre

ip addr add 188.204.140.196/27 brd 188.204.140.223 dev eth0:1 label eth0:1

ip route add 82.94.91.64/28 dev eth0 src 82.94.91.77 table sdsl
ip route add default via 82.94.91.65 table sdsl
ip rule add from 82.94.91.64/28 table sdsl

ip route add 188.204.140.192/27 dev eth0 src 188.204.140.196 table fibre
ip route add default via 188.204.140.193 table fibre
ip rule add from 188.204.140.192/27 table fibre

to check:
ip rule show
ip route list table fibre
ip route list table sdsl

or in /etc/network/interfaces

auto eth0
iface eth0 inet static
        address 82.94.91.77
        netmask 255.255.255.240
        #netmask 255.255.255.255
        network 82.94.91.64
        broadcast 82.94.91.79
        gateway 82.94.91.65
        dns-nameservers 213.75.63.36 194.109.9.99 212.61.33.42 194.109.6.66
        post-up ip route add 82.94.91.64/28 dev eth0 src 82.94.91.77 table sdsl
        post-up ip route add default via 82.94.91.65 table sdsl
        post-up ip rule add from 82.94.91.64/28 table sdsl

        post-down ip rule del from 82.94.91.64/28 table sdsl

        post-up ip addr add 188.204.140.196/27 brd 188.204.140.223 dev eth0:1 label eth0:1
        post-up ip route add 188.204.140.192/27 dev eth0 src 188.204.140.196 table fibre
        post-up ip route add default via 188.204.140.193 table fibre
        post-up ip rule add from 188.204.140.192/27 table fibre

        post-down ip rule del from 188.204.140.192/27 table fibre
        post-down ip addr del 188.204.140.196/27 dev eth0:1

To set a new ip address this way you can flush all ip addresses linked to the device

ip addr flush dev eth0

This also brings the device down, like

ifdown eth0

would.

In order to assign the new IP you need to take it up again

ifup eth0

To change the default gateway the server and programmes launched from it use, you may have to delete the old gateway (it'll only accept one) with

ip route del default via 82.94.91.65

and add the new one with

ip route add default via 188.204.140.193

then change /etc/resolv.conf with

nameserver 213.75.63.36

in the top

More information:

http://linux-ip.net/html/adv-multi-internet.html#ex-adv-multi-internet-outbound-ip-routing

http://www.policyrouting.org/iproute2.doc.html#ss9.5

ip address management

ip address management with ip addr - http://linux-ip.net/html/tools-ip-address.html#tb-tools-ip-addr-scope

ip addr add 188.204.140.195/27 brd 188.204.140.223 dev eth1 label eth1:1

Guide to IP Layer Network Administration with Linux Version 0.4.5 Author: Martin A. Brown - http://linux-ip.net/html/index.html

Asynchronous / Asymmetric / Policy Routing

When using policy routing make sure reverse path filtering is DISABLED

http://tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.kernel.rpf.html

https://access.redhat.com/solutions/53031

# for i in /proc/sys/net/ipv4/conf/*/rp_filter ; do
>  echo 2 > $i 
> done

to see if you're dropping packets

echo 1 >/proc/sys/net/ipv4/conf/<interfacename>/log_martians

http://www.linuxjournal.com/article/7291?page=0,2

using sysctl

https://ams-ix.net/technical/specifications-descriptions/config-guide (11.6)

sysctl -w net.ipv4.conf.
ifname
.rp_filter=0net.ipv4.conf.ifname.rp_filter = 0

This guy also calls it Loopy routing

http://www.policyrouting.org/PolicyRoutingBook/ONLINE/TOC.html

http://www.policyrouting.org/PolicyRoutingBook/ONLINE/CH05.web.html (especially example 5.2.1)

http://www.policyrouting.org/PolicyRoutingBook/ONLINE/CH06.web.html (especially example 6.1.3) is useful for outbound routes through one eth port and downstream through a satellite

http://www.policyrouting.org/iproute2.doc.html#ss9.16

http://www.policyrouting.org/iproute2.doc.html#ss9.5

http://www.lartc.org/lartc.html

http://lartc.org/howto/

Another way is to mask the src in the routing table

http://forums.whirlpool.net.au/archive/206603 eg ip route add default via 2.2.2.1 src 1.1.1.1

OR this way?

https://people.debian.org/~ultrotter/talks/dc10/networking.html

# Asymmetric policy routing
ip route replace table 100 proto static \
  throw 192.168.0.0/16

https://www.ukessays.com/essays/computer-science/asymmetric-routing-splitting-routing-computer-science-essay.php uses SNAT in the iptables

In Linux, we can implement asymmetric routing using iptables (linux 2.4):

iptables -A POSTROUTING -t nat -j SNAT -to 192.168.0.5 -o eth0

This means, for all the packets leaving out via eth0, their source IP address will be altered to 192.168.0.5.

Problems with using mobile phones

As you can't set the routing table for a 4G provider, you can't set the src flag in ip route. If you can get a portable firewall or router to route your 4G connection to your provider maybe you could use the ip route / iptables SNAT options.

http://www.g7smy.co.uk/?p=505 this guy has used a raspberry pi with a ZTE MF 823 (Megafon M100-3) 4G Modem USB thing to do this.

iproute2 howtos

iproute2