What is the difference between bridging and routing?

Bridging and routing are two methods of linking systems via a VPN.

Bridging advantages

  • Broadcasts traverse the VPN -- this allows software that depends on LAN broadcasts such as Windows NetBIOS file sharing and network neighborhood browsing to work.
  • No route statements to configure.
  • Works with any protocol that can function over ethernet, including IPv4, IPv6, Netware IPX, AppleTalk, etc.
  • Relatively easy-to-configure solution for road warriors.

Bridging disadvantages

  • Less efficient than routing, and does not scale well.

Routing advantages

  • Efficiency and scalability.
  • Allows better tuning of MTU for efficiency.

Routing disadvantages

  • Clients must use a WINS server (such as samba) to allow cross-VPN network browsing to work.
  • Routes must be set up linking each subnet.
  • Software that depends on broadcasts will not "see" machines on the other side of the VPN.
  • Works only with IPv4 in general, and IPv6 in cases where tun drivers on both ends of the connection support it explicitly.