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Tunnels
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11.2.6.1. FB6000 doing NAT
If you have a bonded tunnel set implementing a single logical WAN connection, then the FB6000 will typically
have multiple WAN-side IP addresses, one per physical WAN connection. If you are using the FB6000 to NAT
traffic to the WAN, the real source IP address of the traffic will be translated by the NAT process to one of
the IP addresses used by the FB6000.
When this NAT'd traffic is carried via a tunnel, it will be the source address of the tunnel payload packet that
is modified.
Whatever address is used, reply traffic will come back to that address. In order to ensure this reply traffic is
distributed across the tunnel set by the far-end tunnelling device, the address used needs to be an address that
is routed down the tunnel set, rather than one associated with any particular WAN connection.
In order to handle this scenario, the
internal-ip
attribute can be used to define which IP address is used
as the source IP address of the tunnel payload packets.
**TBC do you therefore need at least a /32 public IP that is used by the brick, and is not associated with any
specific WAN connection? So far I have seen NAT used only where there is also a block of public IPs routed
down the tunnel set.**
11.2.6.2. Another device doing NAT
If you are using another device that is performing NAT (for example, a NAT'ing ADSL router) and that device
is on the route that tunnel wrapper packets will take , you may have to set up what is generally called port
forwarding on your NAT'ing router.
If the FB6000 is behind a NAT router, it will not have a public IP address of its own which you can reference
as the far-end IP address on the other end-point device. Instead, you will need to specify the WAN address of
the NAT router for this far-end address. Whether you need to setup a port forwarding rule on your NAT router
depends on whether the FB6000 behind the router has a far-end IP address specified in tunnel definition(s),
as follows :-
• If it does, then it will be sending tunnel wrapper packets via the NAT router such that a session will have
been created in the NAT router by the session tracking functionality that is used to implement NAT (this
assumes there is no outgoing 'firewall' rule on the NAT router that would prevent the wrapper packets from
being forwarded). The established session will mean that UDP packets that arrive from the WAN side will
be passed to the UDP port number that was the source port used in the outgoing wrapper packets.
• If it does not, then you will have to manually setup a port-forwarding rule, since there will have been no
outbound packets to initiate a session. The forwarding rule should specify the UDP port number that is being
used by the tunnel wrapper packets (the
port
attribute value in the tunnel definintion, or the default of 1
if the port is not specified)
11.3. Ether tunnelling
Ether tunnelling provides a mechanism to tunnel layer 2 ethernet traffic between two devices, using the protocol
defined in RFC3378.
An ETUN tunnel provides a link layer 2 connection between two specific physical ports on different FireBricks.
Consider two FireBricks A and B which are able to communicate with each other using IP (eg over the internet).
An otherwise unused port on each FireBrick can be configured as an ETUN port. Every ethernet packet arriving
at FireBrick A's ETUN port is encapsulated and transmitted to FireBrick B (over IP). FireBrick B decapsulates
the packet and transmits it on its configured ETUN port. Ethernet packets received on FireBrick B's ETUN port
are likewise transported to FireBrick A and transmitted from its ETUN port. This mechanism can be used to
extend a LAN over a large physical distance. A typical application would be to enable a single LAN to bridge
two data centres which do not have a direct layer 2 link connection (or to provide alternative backup in the case
that a layer 2 link becomes unavailable).
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