Selecting network for Internet access

I know very little about networking so please bear with me.

I have a Linux box M with two NICs. The first NIC is connected to
network A, whereas the second NIC is connected to network B. Both
networks have an Internet gateway. These gateways are totally independent
from each other.

Currently all Internet traffic on M is sent/received through
network A. Can I dynamically select in M which of the A and B networks to
use for Internet traffic?

Dnia 2011-02-05, o godz. 16:16:54
Clark Smith <(E-Mail Removed)> napisa³(a):


> I know very little about networking so please bear with me.
>
> I have a Linux box M with two NICs. The first NIC is
> connected to network A, whereas the second NIC is connected to
> network B. Both networks have an Internet gateway. These gateways are
> totally independent from each other.
>
> Currently all Internet traffic on M is sent/received through
> network A. Can I dynamically select in M which of the A and B
> networks to use for Internet traffic?


Yes.
1) any dynamic routing protocol, like RIP, OSPF ( the uplinks A and B
need support this)

or

2) http://lartc.org/lartc.html#LARTC.RPDB.MULTIPLE-LINKS

--
Jasiek

Hello,

Clark Smith a écrit :
> I know very little about networking so please bear with me.

Why crosspost into comp.os.linux.misc ?

> I have a Linux box M with two NICs. The first NIC is connected to
> network A, whereas the second NIC is connected to network B. Both
> networks have an Internet gateway. These gateways are totally independent
> from each other.
>
> Currently all Internet traffic on M is sent/received through
> network A. Can I dynamically select in M which of the A and B networks to
> use for Internet traffic?

It depends what you mean exactly by "dynamically".

On 2011-02-05, Pascal Hambourg <boite-a-(E-Mail Removed)> wrote:
> Hello,
>
> Clark Smith a ?crit :
>> I know very little about networking so please bear with me.
>
> Why crosspost into comp.os.linux.misc ?
>
>> I have a Linux box M with two NICs. The first NIC is connected to
>> network A, whereas the second NIC is connected to network B. Both
>> networks have an Internet gateway. These gateways are totally independent
>> from each other.
>>
>> Currently all Internet traffic on M is sent/received through
>> network A. Can I dynamically select in M which of the A and B networks to
>> use for Internet traffic?
>
> It depends what you mean exactly by "dynamically".

There is one default gateway. Only one. You can certainly decide which
one you want to use (route del default, route add default gw a.b.c.d eth1)
However AFAIK you cannot say that "all traffic generated by netscape
goes through A and all traffic generated by skype goes through B" for
example.

On Sat, 05 Feb 2011 16:16:54 +0000, Clark Smith wrote:

> I know very little about networking so please bear with me.
>
> I have a Linux box M with two NICs. The first NIC is connected to
> network A, whereas the second NIC is connected to network B. Both
> networks have an Internet gateway. These gateways are totally
> independent from each other.
>
> Currently all Internet traffic on M is sent/received through
> network A. Can I dynamically select in M which of the A and B networks
> to use for Internet traffic?
>
You might configure that setup for some form of "high availability"
gateway to the internet using network B as a redundant link for network A
(or visa versa). The idea is to monitor the link using network A and be
prepared to switch to network B if network A fails. The elements which
may need to be fixed up upon switching are the default route and name
resolution. A simple script could perform the monitoring.

BTW, at first glance, using both networks seems like an attractive way to
potentially double your bandwidth. Unfortunately, AFAIK, it is not
possible to do that, especially without cooperation from network A and
network B. Theoretically, it could be done, if they both agreed to watch
for your packets and give them special marks of some sort to properly
redirect them back to you. I imagine this is the technique that is used
to bond some link-layer traffic together. For example, there are
protocols for bonded ISDN, bonded T1, bonded DSL, etc. These are
sometimes a viable option to incrementally add bandwidth. The downside is
it can get pricey in a hurry.

--
Douglas Mayne

unruh a écrit :
>
> However AFAIK you cannot say that "all traffic generated by netscape
> goes through A and all traffic generated by skype goes through B" for
> example.

Actually you can do that, under some conditions. You just need to be
able to identify the different flows, then you can route them through
different routes.

Clark Smith wrote:
> I know very little about networking so please bear with me.
>
> I have a Linux box M with two NICs. The first NIC is connected to
> network A, whereas the second NIC is connected to network B. Both
> networks have an Internet gateway. These gateways are totally independent
> from each other.
>
> Currently all Internet traffic on M is sent/received through
> network A. Can I dynamically select in M which of the A and B networks to
> use for Internet traffic?

set default route

man route

Op 5-2-2011 17:16, Clark Smith schreef:
> I know very little about networking so please bear with me.
>
> I have a Linux box M with two NICs. The first NIC is connected to
> network A, whereas the second NIC is connected to network B. Both
> networks have an Internet gateway. These gateways are totally independent
> from each other.
>
> Currently all Internet traffic on M is sent/received through
> network A. Can I dynamically select in M which of the A and B networks to
> use for Internet traffic?

Look for policy routing, Clark

--
Max

Open Source is an ode to common sense

Am 05.02.2011 20:42, schrieb The Natural Philosopher:
> Clark Smith wrote:
>> I know very little about networking so please bear with me.
>>
>> I have a Linux box M with two NICs. The first NIC is connected to
>> network A, whereas the second NIC is connected to network B. Both
>> networks have an Internet gateway. These gateways are totally
>> independent from each other.
>>
>> Currently all Internet traffic on M is sent/received through
>> network A. Can I dynamically select in M which of the A and B networks
>> to use for Internet traffic?
>
> set default route
>
> man route

You would probably also need to get a new ip address and dns server via
dhcp from the internet provider in the other network:

dhcpcd -n
(The command may vary according to your linux version)