iSCSI and NVMe/TCP with VXLAN
Virtual Extensible LAN (VXLAN) extends Layer 2 domains over a Layer 3 data center network. The end devices do not know that their traffic is passing through VXLAN tunnels. Also, the traffic classification based on the DSCP field in the IP header and ECN bits are preserved in VXLAN. Because of these reasons, everything that has been explained in this chapter applies to VXLAN environments as well. Refer to Chapter 7, the section on Lossless Traffic with VXLAN for a brief overview of VXLAN and how traffic classification and ECN bits are preserved. 虚拟可扩展局域网（VXLAN）将第 2 层域扩展到第 3 层数据中心网络。终端设备不知道其流量正在通过 VXLAN 隧道。此外，VXLAN 还保留了基于 IP 头中 DSCP 字段和 ECN 位的流量分类。由于这些原因，本章所解释的所有内容也适用于 VXLAN 环境。有关 VXLAN 以及如何保留流量分类和 ECN 位的简要概述，请参阅第 7 章 "使用 VXLAN 的无损流量 "一节。
Fibre Channel over TCP/IP (FCIP)
FCIP (defined in RFC 3821) is used for replication and backup services among data center sites. Storage arrays in these sites connect to a Fibre Channel fabric, whereas the sites have IP connectivity among them. FCIP transports Fibre Channel frames via a TCP connection, essentially merging the remote fabrics. The FCIP endpoints are switches that have Fibre Channel and Ethernet ports, such as Cisco MDS 9220i. They encapsulate (and decapsulate) FC frames within FCIP, TCP, IP, and Ethernet headers. Refer to Chapter 1, the section on FCIP for FCIP packet format. FCIP（在 RFC 3821 中定义）用于数据中心站点之间的复制和备份服务。这些站点的存储阵列连接到光纤通道结构，而站点之间则有 IP 连接。FCIP 通过 TCP 连接传输光纤通道帧，本质上是合并远程结构。FCIP 端点是具有光纤通道和以太网端口的交换机，如 Cisco MDS 9220i。它们在 FCIP、TCP、IP 和以太网标头中封装（和解封装）FC 帧。有关 FCIP 数据包格式，请参阅第 1 章 FCIP 部分。
TCP Optimizations for Storage Traffic on Cisco FCIP Switches
Those who have experience in operating FCIP may recall that the TCP stack on FCIP switches is enhanced for storage traffic. This achieves high-performance requirements for synchronous and asynchronous replication. The following are these enhancements. 有 FCIP 操作经验的人可能还记得，FCIP 交换机上的 TCP 栈针对存储流量进行了增强。这实现了同步和异步复制的高性能要求。以下是这些增强功能。
1. MTU: Because the maximum Fibre Channel frame size is 2148 bytes, configuring IP MTU of 2300 bytes (after accounting for the headers) on all the links between the FCIP end points avoids fragments, and therefore achieves better performance (Example 8-8). 由于最大光纤通道帧大小为 2148 字节，因此在 FCIP 端点之间的所有链路上配置 2300 字节（考虑报头后）的 IP MTU 可以避免碎片，从而获得更好的性能（例 8-8）。
2. Selective Acknowledgements (SACK): SACK increases performance during packet drops by selectively acknowledging only the received packets, and hence the sender retransmits only the lost packets instead of retransmitting all the packets after the lost packets even if these packets might have reached the receiver. By default, SACK is enabled on Cisco FCIP switches, although Ex
