Symptoms ... In some cases, an active BIG-IP may fail to forward the SYN on the server-side when handling traffic for a mirrored FastL4 virtual after receiving a context ACK from the standby BIG-IP. ... Symptoms include: -- TCP connection failures. -- Possibly other packets lost. ... Impact ... FastL4 mirroring does not always forward SYN to server after receiving context ACK. ... Connections fail. ... Workaround ... Set the tm.fastl4_ack_mirror db variable using the following command: tmsh modify sys db tm.fastl4_ack_mirror value disable ... Fix Information ... In this release, mirrored FastL4 virtual servers now forward the SYN on the server-side after receiving the context-ack from the peer as expected. ... Behavior Change