Information Technology Reference
In-Depth Information
•
Data packaging
—BGP information can be packaged for transmission in multiple
ways. Optimizations are available when commonalities in data or remote peer
attributes are leveraged. These commonalities take advantage of the BGP update
packaging mechanism to drastically reduce the number of packets required.
The following sections examine each of these aspects of the BGP update process, identify
bottlenecks, and recommend features that can improve performance. These aspects are
interdependent. This section concludes with a discussion of the interdependencies.
TCP Protocol Considerations
The two main parameters that affect TCP's performance are the maximum segment size
(MSS) and the TCP window size. The TCP MSS controls the size of the TCP segment, or
packet, and the TCP window size controls the rate at which packets can be sent.
TCP MSS
The TCP MSS for a session is determined at session initiation. This value is advertised
using a TCP option, as described in RFC 793. The TCP MSS option is carried only in the
SYN packet and the corresponding SYN/ACK. The TCP MSS that is used for the TCP
session is the smallest of the advertised TCP MSS options in the SYN packets, as shown in
Figure 3-1.
Figure 3-1
TCP Session Establishment and MSS Determination
TCP SYN
MSS=1460
TCP SYN/ACK
MSS = 536
TCP ACK
