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[Rodolfo Alonso <1705536@xxxxxxxxxxxxxxxxxx>]

Bug closed due to lack of activity, please feel free to reopen if
needed.

** Changed in: neutron
       Status: Triaged => Won't Fix

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https://bugs.launchpad.net/bugs/1705536

Title:
  [RFE] L3-agent agent-backend ovs.

Status in neutron:
  Won't Fix

Bug description:
  The use of linux network namespaces in the l3 agent routers causes a choke point for bandwidth on east/west and north/south traffic.
  In the case of east/west traffic, the source and destination interfaces are known to Neutron and could be routed using Open vSwitch if it is selected as the mechanism_driver for the L2-agent.
  This should allow the l3-agent to be compatible with DPDK and Windows.

  When using network namespaces with Open vSwitch to route an l3 ping packet:
  - arp from source vm -> tap1 (vlan tagging skipped) + broadcast to other ports
  - tap1-> kernel network stack
  - kernel sends arp reply tap1
  - tap1-> source vm (vlan tagging skipped)
  - icmp from source vm -> tap1(vlan tagging skipped)
  - kernel receives icmp on tap1 and send arp request to dest vm via tap2(broadcast)
  - arp via tap2 -> dest vm (vlan tagging skipped)
  - dest vm replies -> tap2
  - kernel updates dest mac and decrement ttl the forward icmp packet to tap2
  - tap2 -> dest vm-> dest vm replies->tap2.(vlan tagging skipped)
  - kernel updates dest mac and decrement ttl the forward icmp reply packet to tap1
  - tap1-> source vm

  When OpenFlow is used to route the same traffic:
  - arp from source vm -> arp rewritten to reply -> sent to source vm ( single openflow action).
  - icmp from source vm -> destination mac update, ttl decremented -> dest vm ( single openflow action)
  - icmp from dest vm -> destination mac update, ttl decremented -> source vm ( single openflow action)

  Introducing a new agent_backend configuration would allow an operator
  to select which implementation is most suitable to their use case.

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