Administrator Guide

Configure the source to send the configured source interface IP address instead of using its front-end IP address in the ICMP unreachable
messages and in the traceroute command output. Use the ip icmp source-interface interface or the ipv6 icmp
source-interface interface commands in Configuration mode to enable the ICMP error messages to be sent with the source
interface IP address. This functionality is supported on loopback, VLAN, port channel, and physical interfaces for IPv4 and IPv6 messages.
feature is not supported on tunnel interfaces. ICMP error relay, PATH MTU transmission, and fragmented packets are not supported for
tunnel interfaces. The traceroute utilities for IPv4 and IPv6 list the IP addresses of the devices in the hops of the path for which ICMP
source interface is configured.
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
Enabling Directed Broadcast
By default, Dell EMC 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 EMC 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
• Specifying the Local System Domain and a List of Domains
• Configuring DNS with Traceroute
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IPv4 Routing