Administrator Guide

Using the Configured Source IP Address in ICMP
Messages
ICMP error or unreachable messages are now sent with the configured IP address of the source interface instead of the front-
end port IP address as the source IP address. Enable the generation of ICMP unreachable messages through the ip
unreachable command in Interface mode. When a ping or traceroute packet from an endpoint or a device arrives at the null 0
interface configured with a static route, it is discarded. In such cases, you can configure Internet Control Message Protocol
(ICMP) unreachable messages to be sent to the transmitting device.
Configuring the ICMP Source Interface
You can enable the ICMP error and unreachable messages to contain the configured IP address of the source device instead of
the previous hop's IP address. This configuration helps identify the devices along the path because the DNS server maps the
loopback IP address to the host name, and does not translate the IP address of every interface of the switch to the host name.
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.
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IPv4 Routing