[Olsr-users] Smart Gateway Feature of 0.6.0

Eric Malkowski (spam-protected)
Mon May 24 18:58:21 CEST 2010

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.

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.

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?

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.  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.

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!


-Eric Malkowski

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