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The computation of the UDP checksum is defined in :
R. Braden, D. Borman, C. Partridge, Computing the Internet Checksum, RFC1071, Septembre 1988
UDP is mainly used for applications where either short messages are exchanged or losses or not a severe problem (either because they can be supported by the application or because they are used in LAN environment where there are almost no losses)
Domain Name System, Network File System (NFS), Remote Procedure Call (RPC), jeux
Multimedia (conversational) applications such as VoIP or VideooverIP often use UDP. In this case, UDP is often combined with RTP
H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson.RTP: A Transport Protocol for Real-Time Applications. RFC1889, Jan 1996
The biggest DDoS attack to date took place in September of 2017. The attack targeted Google services and reached a size of 2.54 Tbps. Google Cloud disclosed the attack in October 2020.
The attackers sent spoofed packets to 180,000 web servers, which in turn sent responses to Google. The attack was not an isolated incident: the attackers had directed multiple DDoS attacks at Google's infrastructure over the previous six months.
Urgent pointer is rarely used and will not be described.
The THL is indicated in blocs of 32 bits. The TCP header may contain options, these will be discussed later.
MSL in IP networks : 120 seconds
MSL in IP networks : 120 seconds
Don’t forget that TCP’s acknowledgements are cumulative.
See e.g.
RFC2001 TCP Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery Algorithms. W. Stevens. January 1997.
Some heavily loaded web servers, use abrupt release to close their connection to avoid maintaining state for 2*MSL seconds.
MSL in IP networks : 120 seconds
Most TCP implementations today have fixes for those problems. We will discuss them later.
Most TCP implementations today have fixes for those problems. We will discuss them later.
This utilization of a hash function to compute the value of the initial sequence number is usually called a SYN cookie.
In practice, the computation of the SYN cookie is slightly more complex than a simple hash function because the server must also remember inside the cookie the following information :
- the MSS value advertised by the client
- the optional utilization of TCP options such as RFC1323 large windows or timestamps or SACK by the sender
The original discussions that lead to the development of the SYN cookie solution may be found in :
http://cr.yp.to/syncookies/archive
Urgent pointer is rarely used and will not be described.
The THL is indicated in blocs of 32 bits. The TCP header may contain options, these will be discussed later.
MSL in IP networks : 120 seconds
MSL in IP networks : 120 seconds
The computation of TCP’s retransmission timer is described in
RFC2988 Computing TCP's Retransmission Timer. V. Paxson, M. Allman. November 2000.
Usual values for alpha and beta are 1/8 and 1/4.
See
P. Karn, C. Partridge, Improving round-trip time estimates in reliable transport protocols, Proc. ACM SIGCOMM87, August 1987
Les timestamps TCP ont étés introduits dans :
RFC1323 TCP Extensions for High Performance. V. Jacobson, R. Braden, D. Borman. May 1992.
L'utilisation de ces timestamps est négociée lors de l'établissement de la connexion TCP. La plupart des implémentations TCP actuelles supportent ces extensions.
See e.g.
RFC2001 TCP Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery Algorithms. W. Stevens. January 1997.
RFC2018 TCP Selective Acknowledgement Options. M. Mathis, J. Mahdavi, S. Floyd, A. Romanow. October 1996.
RFC2018 TCP Selective Acknowledgement Options. M. Mathis, J. Mahdavi, S. Floyd, A. Romanow. October 1996.
Urgent pointer is rarely used and will not be described.
The THL is indicated in blocs of 32 bits. The TCP header may contain options, these will be discussed later.
Some heavily loaded web servers, use abrupt release to close their connection to avoid maintaining state for 2*MSL seconds.