
Tunnels
81
The protocol supports multiple simultaneous tunnels to/from an end-point device, and Local Tunnel ID values
are used on an end-point device to identify each tunnel. The 'scope' of the Local ID is restricted to a single end-
point device - as such, the tunnel itself does not possess a (single) ID value, and is instead identified by the
Local IDs in use at both ends, which may well differ.
11.2.1. Tunnel wrapper packets
The protocol works by wrapping a complete IP packet in a UDP packet, with the destination port number of the
UDP packet defaulting to 1, but which can be set to any other port number if required. These UDP packets are
referred to as the 'tunnel wrappers', and include the digital signature. As with any other UDP traffic originating
at the FB6000, the tunnel wrappers are then encapsulated in an IP packet and sent to the IP address of the far-
end tunnel end-point. The IP packet that is contained in a tunnel wrapper packet is referred to as the 'tunnel
payload', and IP addresses in the payload packet are not involved in any routing decisions until the payload
is 'unwrapped' at the far-end.
Payload packet traffic is sent down a tunnel if the FB6000's routing logic determines that tunnel is the routing
target for the traffic. Refer to Chapter 8 for discussion of the routing processes used in the FB6000. Often, a
dynamic route is specified in the tunnel definition, such that traffic to a certain range of IP addresses (or possibly
all IP addresses, for a default route) is routed down the tunnel when it is in the Up state - see Section 11.2.4
for details.
Tip
Payload IP addressing is not restricted to RFC1918 private IP address space, and so FB105 tunnels
can be used to transport public IP address traffic too. This is ideal where you want to provide public
IP addresses to a network, but it is either impossible to route the addresses directly to the network -
e.g. it is behind a NAT'ing router, or is connected via networks (e.g. a 3rd party ISP) that you have no
control over - or you wish to benefit from having 'portable' public IP addresses e.g. you can physically
relocate a tunnel end-point FB6000 such that it is using different WAN connectivity, yet still have the
same public IP address block routed to an attached network.
11.2.2. Setting up a tunnel
You define a tunnel by creating an
fb105
top-level object. In the web User Interface, these objects are created
and managed under the "Tunnels" category, in the section headed "FB105 tunnel settings".
The basic parameters for a tunnel are :-
•
name
: name of the tunnel (OPTIONAL)
•
local-id
: the Local ID to use for the tunnel (REQUIRED)
•
remote-id
: the ID used at the far-end for this tunnel (this will be the Local ID used on the far-end for
this tunnel) (REQUIRED)
•
secret
: this is a pre-shared secret string that must be set to the same value in the tunnel definitions on
both end-point devices
•
ip
: the IP address of the far-end end-point device (OPTIONAL)
The far-end IP address is optional, and if omitted, tunnel wrapper packets will be sent to the IP address from
which wrapper packets are being received (if any). As such, at least one of the two end-points involved must
have a far-end IP address specified, but it is not necessary for both ends to specify the other. This allows you
to setup a tunnel on an end-point without knowing (or caring) what the far-end IP address is ; this means you
can handle cases such as one of end-points being behind a NAT router that has a dynamic WAN IP address,
or can be used to simplify administration of end-points that are used to terminate a large number of tunnels,
by omitting the far-end IP address in tunnel definitions on such 'shared' end-points. The latter case is typical
where an ISP deploys a FireBrick device to provide a 'head-end' device for tunnel bonding.
Содержание FB6402
Страница 1: ...FireBrick FB6402 User Manual FB6000 Versatile Network Appliance...
Страница 2: ......