Query on IP load balancing using direct routing

[SAMPATHKUMAR KISHORE KANIYAR <sampatki@xxxxxxxxxxxx>]

  Hi,
  
  I am new to the LVS subscription list.
  
  I was going through the paper "Linux Virutal Server for Scalable
  Network Services" by Wensong Zhang maintained in the LVS homepage.
  I found the following explanation in section 3.3 titled "Linux
  Virtual Server via Direct Routing":
  
      "... . The load balancer and the real servers must have one of
      their interfaces physically linked by an uninterrupted segment
      of LAN such as a HUB/Switch. ..."
  
  Again, later on, in section 3.4 titled "Advantages and
  Disadvantages", there exists the following:
  
      ... [For Direct routing] ... "the load balancer and each server
      must be directly connected to one another by a single un-
      interrupted segment of a local-area network".
  
  Is there a scenario and/or real-life example where one does NOT
  use HUB/Switch to physically connect a network interface card?
  Under what scenarios is IP Tunnelling preferred over Direct Routing
  in LVS?
  
  Thanks,
  - Kishore