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GRE
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... PPTP uses an extended version of GRE to carry user PPP packets. These
enhancements allow for low-level ...
... sessions involving a given PNS-PAC pair. A key which is
present in the GRE header indicates which session a particular PPP ...
... control connection.
The GRE header also contains acknowledgment and sequencing
information that is used to perform some level of congestion ...
... MTU for the user data packets encapsulated in GRE is 1532 octets,
not including the IP and GRE ...
... by the PNS to match the Outgoing-Call-Reply
with the Outgoing-Call-Request it issued. It
also is used as the value sent in the GRE
header for mux/demuxing.
...
... PAC to match the Incoming-Call-Reply
with the Incoming-Call-Request it issued.
This value is included in the GRE header of
transmitted data packets ...
... packets are carried between the PAC and PNS, encapsulated in GRE
packets which in turn are carried over IP. The encapsulated ...
... IP Header |
+--------------------------------+
| GRE Header |
+--------------------------------+
...
... header used in PPTP is enhanced slightly from that specified
in the current GRE protocol specification [1, 2 ...
... involves the definition of a new Acknowledgment Number field, used to
determine if a particular GRE packet or set of packets has arrived at
the remote end of the tunnel. This Acknowledgment capability is not
...
... Acknowledgment Number
Contains the sequence number of the highest numbered GRE
packet received by the sending peer for this user session.
...
... flow control by each side of the data exchange. The enhanced GRE
protocol allows packet acknowledgments to be piggybacked on data
packets. Acknowledgments can also be sent separately from data
packets ...
... sequence numbers should never occur since the PAC and PNS never
retransmit GRE packets. A robust implementation will silently
discard duplicate GRE packets, should it receive any.
...
... retransmit GRE packets. A robust implementation will silently
discard duplicate GRE packets, should it receive any.
...
... This section describes how the calculation of ATO is modified in the
case where a time-out does occur. When a time-out occurs, the time-
out value should be adjusted rapidly upward. Although the GRE
packets are not retransmitted when a time-out occurs, the time-out
should be adjusted up toward a maximum limit. To compensate for
...
... in transit without detection.
The GRE packets forming the tunnel itself are not cryptographically
protected. Because the PPP ...
... Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 1701, October 1994. ...
... Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic Routing Encapsulation (GRE) over IPv4 Networks", RFC 1702, October 1994. ...