ECN
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... gained.
The correct operation of ECN requires the cooperation of the receiver
to return Congestion ...
... the possibility that an unscrupulous or poorly implemented receiver
could always clear ECN-Echo and simply not return congestion signals
...
... central role of congestion control, it is prudent to design the ECN
signaling loop to be robust against as many threats as possible. In
...
... signaling loop to be robust against as many threats as possible. In
this way, ECN can provide a clear incentive for improvement over the
prior state-of-the-art without potential incentives for abuse. The
...
... prior state-of-the-art without potential incentives for abuse. The
ECN-nonce is a simple, efficient mechanism to eliminate the potential
abuse of ECN ...
... nonce enables the sender to verify the correct behavior of
the ECN receiver and that there is no other interference that
conceals marked (or dropped) packets in the signaling ...
... receiver and that there is no other interference that
conceals marked (or dropped) packets in the signaling path. The ECN-
nonce protects against both implementation errors and deliberate
...
... receiver.
- does not change other aspects of ECN, nor does it reduce the
benefits of ECN for behaving receivers ...
... - does not change other aspects of ECN, nor does it reduce the
benefits of ECN for behaving receivers.
...
... attacks.
We also note that use of the ECN-nonce has two additional benefits,
even when only drop-tail routers ...
... not elaborate on these benefits in this document.
The rest of this document describes the ECN-nonce. We present an
overview followed by detailed behavior at senders ...
... Congestion Window
Reduced (CWR) signaling mechanism. Familiarity with ECN [ECN] is
assumed. For simplicity, we describe the ECN ...
... ECN [ECN] is
assumed. For simplicity, we describe the ECN-nonce in one direction
only, though it is run in both directions in parallel.
...
... only, though it is run in both directions in parallel.
The ECN protocol for TCP remains unchanged, except for the definition
of a new field in the TCP header ...
... TCP header. As in [RFC3168], ECT(0) or ECT(1)
(ECN-Capable Transport) is set in the ECN field of the IP header ...
... (ECN-Capable Transport) is set in the ECN field of the IP header on
outgoing packets. Congested routers ...
... receivers notice CE, the ECE
(ECN-Echo) flag is set in subsequent acknowledgements until receiving
...
... congestion signals.
The following paragraphs describe aspects of the ECN-nonce protocol
in greater detail.
...
... segments as a large segment, has a simple
answer: ECN is disabled for retransmissions, so can carry no nonce.
...
... starting with sender transmit behavior, then around
the ECN signaling loop, and finish with sender acknowledgement
...
... sum is optional, but recommended, as senders are allowed to
discontinue sending ECN-capable packets to receivers that do not
support the ECN ...
... nonce values are
ignored when calculating the sum (or equivalently a value of zero is
assumed) and ECN-Echo will be set to signal congestion to the sender ...
... nonce sum is checked when an acknowledgement of new data is
received, except during congestion recovery when additional ECN-Echo
signals would be ignored. Checking consists of comparing the correct
...
... with a correction described in the following subsection.
If ECN-Echo is not set, the receiver claims to have received no
...
... congestion window
will be halved, CWR will be set on the next packet with new data
sent, and ECN-Echo will be cleared once the CWR signal is received,
as in [RFC3168 ...
... reduced. When responding to explicit congestion signals, this will
be the first acknowledgement without the ECN-Echo flag set: the
acknowledgement of the packet containing the CWR flag.
...
... sender should ignore the nonce sum returned on any
acknowledgements bearing the ECN-echo flag.
...
... segment is acknowledged.
Finally, in ECN, senders can choose not to indicate ECN capability on
...
... Finally, in ECN, senders can choose not to indicate ECN capability on
some packets for any reason. An ECN-nonce ...
... senders can choose not to indicate ECN capability on
some packets for any reason. An ECN-nonce sender must resynchronize
...
... nonce sender must resynchronize
after sending such ECN-incapable packets, as though a CWR had been
sent with the first new data after the ECN-incapable packets. The
...
... after sending such ECN-incapable packets, as though a CWR had been
sent with the first new data after the ECN-incapable packets. The
sender loses protection for any unacknowledged packets until
...
... sender might infer that a network device has interfered with
correct ECN signaling between ECN-nonce ...
... segments. An incorrect nonce sum
is a sign of misbehavior or error between ECN-nonce supporting
endpoints ...
...
The ECN-nonce can provide robustness beyond checking that marked
packets are signaled to the sender ...
... connection, or provide reliability at the application level.
If robustness against these faults is also desired, then the ECN-
nonce should not be disabled. Instead, reducing the congestion
window ...
... operation while providing continued checking.
The ECN-nonce can also detect misbehavior in Eifel [Eifel ...
... As described in RFC3168, use of the Don't Fragment bit with ECN is
recommended. Receivers that receive unmarked fragments ...
... nonce to conceal a marked fragment. The
ECN-nonce cannot protect against misbehaving receivers that conceal
...
... smaller frame in place of a larger one. Since these smaller packets
are retransmissions, they will be ECN-incapable and bear no nonce.
The sender ...
... the generation function and thus its future output.
Although the ECN-nonce protects against concealment of congestion
...
... ECN signaling mechanism
that improves ECN's robustness by preventing receivers from
concealing marked (or dropped) packets. The intent of this work is
...
... congestion control in the Internet.
The modification retains the character and simplicity of existing ECN
signaling. It is also practical for deployment ...
... codepoints and one TCP header flag (as
well as CWR and ECN-Echo) and has simple processing rules.
...
... Ramakrishnan, K., Floyd, S. and D. Black, "The addition of explicit congestion notification (ECN) to IP", RFC 3168prop, September 2001. ...