Will this (in theory) work, or have I been around too much magic smoke
that has escaped from fried equipment???
I have a system with two different internet connections. One connection
is a WISP via an external bridging radio (ethernet to proprietary
wireless back haul). The other connection is PPPoE ADSL via the local
phone company.
(I think) I am wanting to use equal cost multi path routing to try to
utilize both of these connections. After reading some other information
I'm not entirely sure that I do want to use ECMP routing. However, this
is out side of this discussion.
To utilize ECMP routing, you need two or more static upstream gateways.
The problem is that one of my upstream gateways is dynamic via PPPoE.
Thus I do not have two static default routes to add via the "ip route
... nexthop ..." command.
So, my proposed theoretical solution. (At least so far it has sounded
good in my head.) Use socat (http://www.dest-unreach.org/socat/)to
create a pair of virtual TUN interfaces that are connected with each
other. With these two additional virtual TUN interfaces, I *THINK* I
can split the routing in to multiple tables. The main routing table
would contain lo, eth0 (WISP), tun0, and eth2 (internal LAN). While the
virtualRouter routing table would contain tun1 and eth1 (ADSL). If I
use ip rule(s) to determine which routing table to use, I think I can
get the system to virtually act like two different routers. The hope is
that I can put a common subnet on tun0 and tun1 that exists in both
routing tables, but with only one interface local to each routing table.
Thus each routing table will (hopefully) think that it has to go
across the virtual point to point interface to reach the other end of /
IP on the subnet.
*IF*, and this is a big if, I can get this to work like I've tried to
explain, I think I can have the virtual (non default / main) router do
nothing but translate the PPPoE to raw IP thus presenting an additional
upstream static IP to the main system, thus allowing the main system to
see two static upstream gateways.
Ultimately I see the routing tables as such:
main routing table(s):
lo: 127.0.0.1/8
eth0: A.B.C.D/24 (WISP)
eth2: 192.168.0.254/24 (LAN)
tun0: 192.168.1.253/24 (virtual point-to-point)
virtualRouter routing table(s):
lo: 127.0.0.1/8
eth1: (PPPoE ADSL)
tun1: 192.168.1.254/24 (virtual point-to-point)
ppp0: M.N.O.P/24 (ADSL ISP)
Some packet flow might help make it easier to understand. Traffic
flowing from the LAN out through the main system out through the PPPoE
would pass through the system as such:
1) In the eth2 LAN interface out the tun0 virtual interface.
2)**In the tun0 virtual interface out tun1 virtual interface.**
3) In the tun1 interface out the ppp0 interface.
4) In the ppp0 interface out the eth0 (ADSL) interface.
Returning traffic would take this path:
1) In the eth0 (ADSL) interface out the ppp0 interface.
2) In the ppp0 interface out the tun1 interface.
3)**In the tun1 interface out the tun0 interface.**
4) In the tun0 interface out the eth2 (LAN) interface.
Steps 2 and 3 respectively (*ed lines) are where the traffic would go
from one routing table to the other.
So, now that I have tried to explain what I'm wanting to do, and
probably thoroughly made a mess of it, do you think that at least in
theory this is possible?
Grant. . . .
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