Re: Re: [LARTC] multipath routing problem [Shorter version] - Help

[Julian Anastasov <ja@ssi.bg>]

	Hello,

On 25 Oct 2002, Vincent Jaussaud wrote:

> But traffic is NAT-ed after multipath routing occurs !
> Eg, the box which do multipath routing do not NAT traffic; traffic get
> NAT-ed when leaving the gateways:
>
> LAN --> FW w/ multipath-routing
> 	   |		|
> 	  Gateway1  Gateway2
> 	   | (NAT)	| (NAT)
> 	   |		|
> 	-------------------- Remote Network
>
> Packets reach the Remote Network using one of the Gateway NAT-ed IP, so
> that when packets come back they should use the proper return path. Am I
> wrong ?

	Now I see, then the TOS is a big problem for you. May
be your problem will be solved if TOS is not a routing key but
it does not sound as a thing that is easy to fix in kernel.

> Hmmm... Then this is where the problem is. So, if I understand
> correctly, packets coming from a single TCP connections will use any of
> the multipath route _if_ they are not NAT-ed ? Isn't the routing cache

	Yes, traffic A->B with TOS=XXX will use one path, traffic
A->B with TOS=YYY can use different path.

> suppose to ensure that every packets coming from a single connection use
> the same path ?

	The routing does not cache connections but route resolutions keyed
by saddr, daddr, tos, etc. Even there are no TCP/UDP ports (yet?).

> Now, If I understand the whole topic, in order to fix my problem, I need
> to:
>
> 	- NAT everything on the FW itself

	This is a solution

> 	- or disable NAT on both gateways, and ensure that routing is done
> properly

	Not sure what you mean. But you can run multipath routes
on the both gateways. Then the internal hosts can select any of
the gateways as default (or to use alternative default gateways).
Another solution is your apps not to change the TOS, it can be
changed at the border gateways (if useful at all).

> Am I right ? I'm becomming a bit lost, here :-\
>
> Many Thanks for your time.
> Vincent.

Regards

--
Julian Anastasov <ja@ssi.bg>

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