Users Guide

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
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 configured 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 configuration, use the show config command in INTERFACE mode.
Resolution of Host Names
Domain name service (DNS) maps host names to IP addresses. This feature simplifies commands such 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.
In a dual stack setup, the system sends both A ( for IPv4 — RFC 1035) and AAAA ( for IPv6 — RFC 3596) record requests to a
DNS server even if you configure only the ip name-server command.
The following sections describe DNS and the resolution of host names.
• Enabling Dynamic Resolution of Host Names
IPv4 Routing 351