[LARTC] bandwidth aggregation between 2 hosts in the same subnet

[Grant Taylor]

On 07/31/07 10:31, Ralf Gross wrote:
> I've talked to one of the people of the network staff. He meant they
> never used CEF in this type of scenario. I'm also not very familiar
> with Cicso products.

My physical scenario is a Cisco 3640 router with two (10BaseT) ethernet 
connections connected to external ethernet to SDSL bridging modems.  The 
SDSL modems bridge the ethernet to an ATM circuit.  The ATM circuit is 
terminated in a Cisco 7206 (I think it's a 6) UBR router at my ISP.

Cisco Express Forwarding is being run on the local 3640 and the remote 
7206 to control which connection the packets are being routed down.  The 
local 3640 has two routes upstream, each being the remote IP for each of 
the ATM links.  Correspondingly the 7206 has two routes to a (globally) 
routable subnet behind the local 3640.

As I understand it, CEF (ultimately) builds a forwarding information 
base (a.k.a. FIB) from the routing tables.  So if you have multiple 
routes, CEF will know about them.  CEF will then divide the traffic 
either "per flow" or "per packet" across all available routes so that 
more aggregate bandwidth is achieved.

In my scenario, I am using CEF via OSPF to combine two 1.1 Mbps SDSL 
connections to get close to 2 Mbps worth of aggregate bandwidth to the 
net.  I can and do routinely receive 1.5 - 1.8 Mbps throughput via FTP / 
HTTP / BitTorrent.  (Though BitTorrent by nature is not the best example)

> If you could give me more details on your CEF setup, that would maybe
> help me to show them what a CEF config should look like.

I think I have done so above.  If you want config examples, contact me 
off list as I don't want to publish it to the world.

> But I'm still not sure if CEF is a thing that is designed to work
> with client-client connections.

I can't say for sure one way or the other. but It think that CEF will 
achieve what you are wanting to do as long as the device you are 
connecting to will support it.  I know that more and more layer 3 
devices support it.  So, that being said if your switches are recent 
layer 3 switches, I'd say that they will support CEF.  I don't know for 
sure though.



Grant. . . .