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How does ODL work at Layer 2?

I have ODL installed and I can install/delete/etc flows mostly with no issues. Now I am trying to figure out how to actually make it work in a production style environment. My question pertains to this situation:

PHYSICAL: hostA - to - l2A (non-of-switch) - to - router1 (of-router) - l2B (non-of-switch) - to - hostB

LOGICAL: hostA (10.1.1.10/24) - vlan10, Default GW router1 hostB (10.2.2.10/24- vlan20, Default GW router1

TEST: ping hostB from hostA

CONFUSION: So hostA will send the icmp traffic to it's default gateway (the openflow router1 in the middle), where I would presumably have a flow that matches on src mac/ip address/vlanid/etc info and then send the echo-request out the port to l2B. Great. My confusion comes when you consider that the src/dst frame headers will be left unchanged when router1 forwards the ping out towards l2B (it would still have the src mac of hostA and the dst mac of hostA's default gw)... I know you can change the src/dst mac-addresses in a flow, done that in testing, but I don't want to have to know the mac address of 100's or 1000's of hosts and have them explicitly layer2 "NATed" with each flow.

I'm new to this SDN stuff, so if someone could help me understand how this is solved on ODL and maybe point me in a documentation direction, I would be grateful!

Thanks,

Steve