Dell S3048-ON, Configuration Manual

Page: 365 / 1036

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.
IPv4 Routing 365