On Tue, Oct 28, 2014 at 07:44:48, A, Keshava wrote:
> Hi,
> Current Open-stack was built as flat network.
> With the introduction of the L3 lookup (by inserting the routing table
> in forwarding path) and separate 'VIF Route Type' interface:
> At what point of time in the packet processing  decision will be made
> to lookup FIB  during ? For each packet there will additional  FIB
> lookup ?
> How about the  impact on  'inter compute traffic', processed by  DVR  ?
> Here thinking  OpenStack cloud as hierarchical network instead of Flat
> network ?


It's difficult for me to answer in general terms: the proposed specs are 
general enough to allow multiple approaches to building purely-routed networks 
in OpenStack, and they may all have slightly different answers to some of these 
questions. I can, however, speak about how Project Calico intends to apply them.

For Project Calico, the FIB lookup is performed for every packet emitted by a 
VM and destined for a VM. Each compute host routes all the traffic to/from its 
guests. The DVR approach isn't necessary in this kind of network because it 
essentially already implements one: all packets are always routed, and no 
network node is ever required in the network.

The routed network approach doesn't add any hierarchical nature to an OpenStack 
cloud. The difference between the routed approach and the standard OVS approach 
is that packet processing happens entirely at layer 3. Put another way, in 
Project Calico-based networks a Neutron subnet no longer maps to a layer 2 
broadcast domain.

I hope that clarifies: please shout if you'd like more detail.


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