- Real network interface:
- Real network interface =
a network card that
a node uses to
tranmsmit
physical frames
Example:
- Ethernet interface
- Real network interface =
a network card that
a node uses to
tranmsmit
physical frames
- Virtual
network interface:
- Virtual network interface =
an abstract representation
(= object)
of a computer network interface
- A Virtual network interface can
be mapped:
- To a real network interface or
- To a IP destination (this is the more common usage)
- Virtual network interface =
an abstract representation
(= object)
of a computer network interface
- Recall the format of the
(Layer 2) Forwarding Table
Layer 2 forwarding table +---------------+--------------------+ | Dest NetID | Port (Interface) | +---------------+--------------------+ | IP netw 1 | #1 | +---------------+--------------------+ | ..... | ..... | +---------------+--------------------+
- Layer 2 forwarding table
with virtual interfaces:
Layer 2 forwarding table +---------------+----------------------+ | Dest NetID | Port (Interface) | +---------------+----------------------+ | IP netw 1 | #1 | <---- Real interface +---------------+----------------------+ | IP netw 2 | Destination IP addr | <---- Virtual interface +---------------+----------------------+
- Note:
- It is clearly
stupid to:
- Transmit an IP packet using another IP packet
- The novelty of
transmit an
inner IP packet using
an outer IP packet is the
fact that:
- The inner IP packet is transformed in some way.
- It is clearly
stupid to:
- Processing
prior to
encapsulation:
- The virtual interface
often has an associated
special (packet)
processing handler to provide
optional processing
- The handler routine can
be part of the
virtual interface specification:
Layer 2 forwarding table +---------------+-------------------------------+ | Dest NetID | Port (Interface) | +---------------+-------------------------------+ | IP netw 1 | #1 | +---------------+-------------------------------+ | IP netw 2 | Destination IP addr, handler | +---------------+-------------------------------+
- The virtual interface
often has an associated
special (packet)
processing handler to provide
optional processing
-
Processing on each
type of
interfaces:
- Forwarding a
packet on
a real (= physical)
network interface
- The packet is
transmitted in a
physical network frame
E.g.: in an Ethernet frame
- The packet is
transmitted in a
physical network frame
- Forwarding a
packet on
a virtual
network interface
- The IP packet is
optionally
pre-processed
- Example: encrypted
- Then the packet is
encapsulated:
- The outer IP packet is then forwarded (using the forwarding/routing tables)
- The IP packet is
optionally
pre-processed
- Example:
- Suppose a
router has the following
virtual interface entry:
- Then an IP packet destined for
the IP network 7.7.7.0:
will be forwarded as follows:
- Network 7.7.7.0 found
in forwarding table with
virtual entry:
The router will encapsulate (optionally with some pre-processing):
- Then the encapsulated IP packet is
forwarded:
According to the routing table, the encapsulated IP packet will be forwarded to the default router !!!
- The encapsulated IP packet
will eventually arrive
at the destination router of
the virtual interface:
- Network 7.7.7.0 found
in forwarding table with
virtual entry:
- Suppose a
router has the following
virtual interface entry:
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