- Consider an
arbitrary
TCP connection request:
Question:
- Is the TCP connection request
always a
valid request ???
- Can such a
request be
bogus ???
(And how to process bogus requests ???)
- Is the TCP connection request
always a
valid request ???
- "Creating" a
bogus
TCP connection request
- The client
picks the random number 7625
and
sends a
(valid) connection request
to the server:
However:
- the connection request message is delayed !!!
- The client
times out and ...
retransmits
the (same) connection request message
to the server.
Suppose:
- The retransmitted connection request is received first
- Suppose: the
(second) connection is
established and
closed
- The client and
server
finished the
TCP connection protocol
- The client and
server
exchanged
a few messages
- The client and server then closed the TCP connection
All the while, the first (delayed) connection request has not been received:
- The client and
server
finished the
TCP connection protocol
- After
the client/server
closed the
TCP connection,
the delayed connection request
arrives:
Clearly:
- The delayed connection request is a bogus request !!!!
- The client
picks the random number 7625
and
sends a
(valid) connection request
to the server:
- Fact 1:
- The bogus connection request
is
indistinguishable
from a
legitimate connection request
In fact:
- If the connection request was not received, the connection request would have been a legitimate connection request !!!
- The bogus connection request
is
indistinguishable
from a
legitimate connection request
- Fact 2:
- The server does
not have
any information that:
- Allow the server to decide whether the connection request is bogus or legitimate.
Conclussion from fact 2:
- The server will
process a
bogus connection request
as if it is a
legitimate connection request
(Because the server cannot tell the difference)
- The server does
not have
any information that:
- Fact 3:
- The
client
does have the
necessay
information
that:
- Allow the client to decide whether the connection request is bogus or legitimate.
- For a
legitimate connection request:
- The client has
created a
partially filled
TCP state record:
- The client has
created a
partially filled
TCP state record:
- For a
bogus connection request:
- The client has a no TCP state record !!!
Conclussion from fact 3:
- The client is able to process a bogus connection request differently from a legitimate connection request !!!!!!
- The
client
does have the
necessay
information
that: