[Olsr-users] Smart Gateway Feature of 0.6.0

[Henning Rogge]

Am Montag 24 Mai 2010, 18:58:21 schrieb Eric Malkowski:
> Hi All-
> 
> I had a look at the sourcecode readme, sample config files and such for
> 0.6.0 and didn't find anything written up about the Smart Gateway feature.
Look into REAMDE-Olsr-Extensions.

> So I'm curious if it might help the following situation:
> 
> For example a simple mesh setup with several nodes where 2 of them have
> internet connectivity and each internet gateway uses NAT for clients on
> the private mesh network w/ any attached HNAs etc.
> Each of the internet connected gateways use dyn-gw to remove their
> default route when they detect their internet connection is no good.
> This way anyone in the mesh can use the other healthy gateway when one
> of the two is down.
As soon as the HNA times out, the other nodes will switch the gateway. 
Unfortunately there is no way in OLSRv1 to revoke a HNA, so it might take some 
time, depending on the settings of your mesh.

> When clients using one gateway (downloading a file via TCP from the
> internet for instance) has that gateway go down, they will switch to the
> other gateway, but TCP obviously will have to start over since the
> internet server thinks the client is coming from two different places.
> It is not bad for light web browsing, but services that are more
> "persistent" will have trouble.
> 
> Does the Smart Gateway feature overcome this problem and if so, how?
If you have two gateways and both of them are using NAT, you cannot solve the 
feature unless you use a VPN of your own to connect to a VPN server in the 
internet (and make sure your "source ip" does not change).
 
> Even if the two gateway machines shared NAT information, they both have
> different public IP addresses, so internet servers can't adapt to client
> packets for the same TCP session going through the two different
> gateways when a gateway switch happens during the TCP session.
Switching between two NAT gateways will break all TCP sessions, even with 
smart-gateway.

> The only
> thing I think that would work is if each gateway did a VPN tunnel to a
> 3rd machine that lives on the internet in a datacenter somewhere (or
> wherever a very "reliable" internet connection exists) and only at that
> one machine would packets enter the internet.  This way one NAT is
> taking care of all mesh address space to internet address space and it
> doesn't matter how the traffic made it to the "datacenter" machine from
> the various mesh gateways that have internet presence via VPN tunnel to
> the "master" NAT machine.
> 
> I hope I'm making enough sense here.
Yes.
 
> I'll be curious to hear what you guys have to say.  If someone has setup
> a topology diagram that takes advantage of the Smart Gateway feature, I
> would love to see it!
The primary advantage of smartgateway is that your gateway does not change 
constantly if you have to different gateways with similar ETX cost. You can 
stick to one of the gateways even if the other one becomes a little bit 
"closer".

Henning Rogge

-- 
1) You can't win.
2) You can't break even.
3) You can't leave the game.
— The Laws of Thermodynamics, summarized
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 198 bytes
Desc: This is a digitally signed message part.
URL: <http://lists.olsr.org/pipermail/olsr-users/attachments/20100524/17db9912/attachment.sig>