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Dell EMC Configuration Guide for the S4048T–ON System 9.14.2.4

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Configuring the Duration to Establish a TCP Connection

You can configure the duration for which the device must wait before it attempts to establish a TCP connection. Using this capability, you can limit the wait times for TCP connection requests. Upon responding to the initial SYN packet that requests a connection to the router for a specific service (such as SSH or BGP) with a SYN ACK, the router waits for a period of time for the ACK packet to be sent from the requesting host that will establish the TCP connection.

You can set this duration or interval for which the TCP connection waits to be established to a significantly high value to prevent the device from moving into an out-of-service condition or becoming unresponsive during a SYN flood attack that occurs on the device. You can set the wait time to be 10 seconds or lower. If the device does not contain any BGP connections with the BGP neighbors across WAN links, you must set this interval to a higher value, depending on the complexity of your network and the configuration attributes.

To configure the duration for which the device waits for the ACK packet to be sent from the requesting host to establish the TCP connection, perform the following steps:

  1. Define the wait duration in seconds for the TCP connection to be established.
    CONFIGURATION mode
    DellEMC(conf)#ip tcp reduced-syn-ack-wait <9-75>
    You can use the no ip tcp reduced-syn-ack-wait command to restore the default behavior, which causes the wait period to be set as 8 seconds.
  2. View the interval that you configured for the device to wait before the TCP connection is attempted to be established.
    EXEC mode
    DellEMC>show ip tcp reduced-syn-ack-wait

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