View source for 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
<pre>
sysctl net.ipv4.ip_forward
</pre>
or
<pre>
echo 1 > /proc/sys/net/ipv4/ip_forward
</pre>

= Multiple Connections to the Internet / two isps on one nic =

/etc/shorewall/interfaces
<pre>
net     eth0    82.94.91.79,188.204.140.224 routeback
</pre>

/etc/postfix/main.cf
<pre>
add 188.204.140.192/27 to mynetworks
</pre>

/etc/iproute2/rt_tables

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

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

<pre>
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
</pre>

or in /etc/network/interfaces
<pre>
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
</pre>

To set a new ip address this way you can flush all ip addresses linked to the device
<pre>
ip addr flush dev eth0
</pre>
This also brings the device down, like
<pre>
ifdown eth0
</pre>
would.

In order to assign the new IP you need to take it up again
<pre>
ifup eth0
</pre>

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

<pre>
ip route del default via 82.94.91.65
</pre>

and add the new one with

<pre>
ip route add default via 188.204.140.193
</pre>

then change /etc/resolv.conf with
<pre>
nameserver 213.75.63.36
</pre>
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

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

to see if you're dropping packets
<pre>
echo 1 >/proc/sys/net/ipv4/conf/<interfacename>/log_martians
</pre>

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

using sysctl

https://ams-ix.net/technical/specifications-descriptions/config-guide (11.6)
<pre>
sysctl -w net.ipv4.conf.
ifname
.rp_filter=0net.ipv4.conf.ifname.rp_filter = 0
</pre>

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

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

== 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}}