[clug] A routing question

Robert Edwards bob at cs.anu.edu.au
Wed Apr 18 23:30:06 GMT 2007

This is a bit hard to do if you are in a residential college and looking
for ways around the rate-limiting between your college room and the rest
of the (ANU) campus networks... :-)

Chris, you might want to look at using IP over IP and SNAT - that is one
way we have used in the past to achieve something similar to what you
are looking at. Of course, I am only speaking theoretically...

Bob Edwards.

Kim Holburn wrote:
> It really depends on what sort of routers you have and how much you 
> control them.
> The simplest way would probably be to remove the A to B link.  What do 
> you need it for anyway?
> Make all the machines on subnet A use the router that handles A to C.  
> Tell the A to C router that subnet B traffic goes to the router handing 
> C to B.  On subnet B tell the router that to find subnet A go the the 
> router handing B to C.
> On 2007/Apr/18, at 3:54 PM, Christopher Zhang wrote:
>> Hi list,
>> Say if the connections from subnet A to B are throttled down, but the 
>> connections from subnet A to C and from subnet B to C aren't. The way 
>> the connections are throttled is by applying rules on the default 
>> gateways of subnets A and B.
>> Is there a way to speed up the connections from subnet A to B?
>> The closest idea I can think of is to setup a gateway within subnet A, 
>> let's call it D. Setup a host in subnet C, let's call it E, and 
>> finally another gateway in subnet B, and call it F.
>> The idea is to route all traffic from subnet A to C, then bounce it 
>> off C to B. Since the connections from A to C and B to C are fast, 
>> this effectively increases speed from A to B. So instead of using the 
>> default gateways for subnet A and B, we can use our own new gateway D, 
>> then somehow pipe all traffic to E, and then from E pipe all traffic 
>> to our new gateway F in subnet B.
>> The reason this increases the speed from subnet A to B is that the 
>> connection is unthrottled from subnet A to C, and from subnet C to B.
>> Eventually this is like a man in the middle setup, in subnet A, tell 
>> all machines to use D as the default gateway. What D does is to 
>> forward to the traffic to E, D still uses the real default gateway for 
>> subnet A to do that however since this connection is to host E in an 
>> unaffected subnet, the connection is fast. Then E forwards whatever is 
>> forwarded to it to F, if we tell all computers to use F in subnet B, 
>> the traffic will reach any host fin subnet B, without any speed loss.
>> It is easy to setup D as a gateway and route traffic through it, but 
>> how can I tell D to route the traffic to E (in subnet C) and from E 
>> route all traffic to F (in subnet B)? I cannot tell D to use E as the 
>> default gateway since they are on different subnets. If I use iptables 
>> to forward the traffic, the packet will lose the original header which 
>> means the reverse won't come through.
>> Maybe a tunnel needs to be setup, but I have no idea how to do that, 
>> does anyone have better ideas?
>> Thanks
>> Chris
>> --linux mailing list
>> linux at lists.samba.org
>> https://lists.samba.org/mailman/listinfo/linux
> -- 
> Kim Holburn
> IT Network & Security Consultant
> Ph: +39 06 855 4294  M: +39 3494957443
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