Users Guide

Conguring the Duration to Establish a TCP Connection
This functionality is supported on the S4820T platform.
You can congure the amount of time 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 specic 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 signicantly high value to prevent the
device from moving into an out-of-service condition or becoming unresponsive during a SYN ood 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 conguration
attributes.
To congure 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. Dene the wait duration in seconds for the TCP connection to be established.
CONFIGURATION mode
Dell(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 congured for the device to wait before the TCP connection is attempted to be established.
EXEC mode
Dell>show ip tcp reduced-syn-ack-wait
Enabling Directed Broadcast
By default, Dell Networking OS drops directed broadcast packets destined for an interface. This default setting provides some
protection against denial of service (DoS) attacks.
To enable Dell Networking OS to receive directed broadcasts, use the following command.
• Enable directed broadcast.
INTERFACE mode
ip directed-broadcast
To view the conguration, use the show config command in INTERFACE mode.
Resolution of Host Names
Domain name service (DNS) maps host names to IP addresses. This feature simplies such commands as Telnet and FTP by allowing
you to enter a name instead of an IP address.
Dynamic resolution of host names is disabled by default. Unless you enable the feature, the system resolves only host names entered
into the host table with the ip host command.
The following sections describe DNS and the resolution of host names.
• Enabling Dynamic Resolution of Host Names
• Specifying the Local System Domain and a List of Domains
• Conguring DNS with Traceroute
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IPv4 Routing