RestartModeB.seq - COOKIE ECHO chunk is received when a TCB exists (Case B)
To check that if COOKIE ECHO chunk is received when a TCB exists in mode B
then the endpoint should update its peer's Verification Tag from the State
Cookie, stop any init or cookie timers that may be running, and send a
COOKIE-ACK.
./RestartModeB.seq [-tooloption ...] -pkt ./RestartModeB.def
-tooloption : v6eval tool option
See Also: ../common/STD_PKT_COMMON.def
../common/SCTP_COMMON.def
Association not established between endpoint A and B. Also arrange the
data in endpoint B such that upper layers send Associate primitive to
startup an association with endpoint A.
Endpoint A Endpoint B ULP
(CLOSED) (CLOSED)
<----- Associate
<----------------- INIT
INIT ----------------->
<----------------- INIT-ACK
COOKIE-ECHO ----------------->
<----------------- COOKIE-ACK
Communication Up ---------->
TEST DESCRIPTION:
1. Try to send a COOKIE-ECHO message when a TCB exists from
endpoint A to B.
2. Check A: COOKIE-ECHO message is accepted and COOKIE-ACK message
is received at endpoint A.
None
RFC 4960
5.2.4. Handle a COOKIE ECHO when a TCB Exists
5) Refer to Table 2 to determine the correct action to be taken.
+------------+------------+---------------+--------------+-------------+
| Local Tag | Peer's Tag | Local-Tie-Tag |Peer's-Tie-Tag| Action/ |
| | | | | Description |
+------------+------------+---------------+--------------+-------------+
| X | X | M | M | (A) |
+------------+------------+---------------+--------------+-------------+
| M | X | A | A | (B) |
+------------+------------+---------------+--------------+-------------+
| M | 0 | A | A | (B) |
+------------+------------+---------------+--------------+-------------+
| X | M | 0 | 0 | (C) |
+------------+------------+---------------+--------------+-------------+
| M | M | A | A | (D) |
+======================================================================+
| Table 2: Handling of a COOKIE ECHO when a TCB Exists |
+======================================================================+
Legend:
X - Tag does not match the existing TCB.
M - Tag matches the existing TCB.
0 - No Tie-Tag in cookie (unknown).
A - All cases, i.e., M, X, or 0.
Note: For any case not shown in Table 2, the cookie should be
silently discarded.
Action
A) In this case, the peer may have restarted. When the endpoint
recognizes this potential 'restart', the existing session is
treated the same as if it received an ABORT followed by a new
COOKIE ECHO with the following exceptions:
- Any SCTP DATA chunks MAY be retained (this is an
implementation-specific option).
- A notification of RESTART SHOULD be sent to the ULP instead of
a "COMMUNICATION LOST" notification.
All the congestion control parameters (e.g., cwnd, ssthresh)
related to this peer MUST be reset to their initial values (see
Section 6.2.1).
After this, the endpoint shall enter the ESTABLISHED state.
If the endpoint is in the SHUTDOWN-ACK-SENT state and recognizes
that the peer has restarted (Action A), it MUST NOT set up a new
association but instead resend the SHUTDOWN ACK and send an ERROR
chunk with a "Cookie Received While Shutting Down" error cause to
its peer.
B) In this case, both sides may be attempting to start an association
at about the same time, but the peer endpoint started its INIT
after responding to the local endpoint's INIT. Thus, it may have
picked a new Verification Tag, not being aware of the previous tag
it had sent this endpoint. The endpoint should stay in or enter
the ESTABLISHED state, but it MUST update its peer's Verification
Tag from the State Cookie, stop any init or cookie timers that may
be running, and send a COOKIE ACK.
C) In this case, the local endpoint's cookie has arrived late.
Before it arrived, the local endpoint sent an INIT and received an
INIT ACK and finally sent a COOKIE ECHO with the peer's same tag
but a new tag of its own. The cookie should be silently
discarded. The endpoint SHOULD NOT change states and should leave
any timers running.
D) When both local and remote tags match, the endpoint should enter
the ESTABLISHED state, if it is in the COOKIE-ECHOED state. It
should stop any cookie timer that may be running and send a COOKIE
ACK.
Note: The "peer's Verification Tag" is the tag received in the
Initiate Tag field of the INIT or INIT ACK chunk.