Setup Guide

Direct, Lo 0
--More--
Dell EMC Networking OS installs a next hop that is on the directly connected subnet of current IP address on the interface.
Dell EMC Networking OS also installs a next hop that is not on the directly connected subnet but which recursively resolves to a next hop
on the interface's configured subnet.
• When the interface goes down, Dell EMC Networking OS withdraws the route.
• When the interface comes up, Dell EMC Networking OS re-installs the route.
• When the recursive resolution is “broken,” Dell EMC Networking OS withdraws the route.
• When the recursive resolution is satisfied, Dell EMC Networking OS re-installs the route.
Configure Static Routes for the Management
Interface
When an IP address that a protocol uses and a static management route exists for the same prefix, the protocol route takes precedence
over the static management route.
To configure a static route for the management port, use the following command.
• Assign a static route to point to the management interface or forwarding router.
CONFIGURATION mode
management route ip-address mask {forwarding-router-address | ManagementEthernet slot/port}
To view the configured static routes for the management port, use the show ip management-route command in EXEC privilege
mode.
DellEMC#show ip management-route
Destination Gateway State Route Source
----------- ------- ----- ------------
10.16.0.0/16 ManagementEthernet 1/1 Connected Connected
172.16.1.0/24 10.16.151.4 Active Static
IPv4 Path MTU Discovery Overview
The size of the packet that can be sent across each hop in the network path without being fragmented is called the path maximum
transmission unit (PMTU). This value might vary for the same route between two devices, mainly over a public network, depending on the
network load and speed, and it is not a consistent value. The MTU size can also be different for various types of traffic sent from one host
to the same endpoint.
Path MTU discovery (PMTD) identifies the path MTU value between the sender and the receiver, and uses the determined value to
transmit packets across the network. PMTD, as described in RFC 1191, denotes that the default byte size of an IP packet is 576. This
packet size is called the maximum transmission unit (MTU) for IPv4 frames. PMTD operates by containing the do not fragment (DF) bit
set in the IP headers of outgoing packets. When any device along the network path contains an MTU that is smaller than the size of the
packet that it receives, the device drops the packet and sends an Internet Control Message Protocol (ICMP) Fragmentation Needed
(Type 3, Code 4) message with its MTU value to the source or the sending device. This message enables the source to identify that the
transmitted packet size must be reduced. The packet is retransmitted with a lower size than the previous value. This process is repeated
in an interactive way until the MTU of the transmitted packet is lower or equal to the MTU of the receiving device for it to obtain the
packet without fragmentation. If the ICMP message from the receiving device, which is sent to the originating device, contains the next-
hop MTU, then the sending device lowers the packet size accordingly and resends the packet. Otherwise, the iterative method is followed
until the packet can traverse without being fragmented.
To use the PMTD functionality, you must enter the ip unreachables command on a VLAN interface to enable the generation of
ICMP unreachable messages in the intermediate nodes. The PMTD functionality is based on the ICMPv4 destination unreachable message
which is generated by the intermediate device only when the ip unreachables command is configured. PMTD is supported on all the
layer 3 VLAN interfaces. Since all of the Layer 3 interfaces are mapped to the VLAN ID of 4095, you cannot configure unique layer 3 MTU
values for each of the layer 3 interfaces. If a VLAN interface contains both IPv4 and IPv6 addresses configured on the system, both the
IPv4 and IPv6 traffic are applied the same MTU size; you cannot specify different MTU values for IPv4 and IPv6 packets.
IPv4 Routing
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