Administrator Guide

CONFIGURATION mode
management route ip-address mask {forwarding-router-address | ManagementEthernet
slot/port}
Example of the show ip route static Command
To view the configured static routes for the management port, use the show ip management-route
command in EXEC privilege mode.
Dell#show ip management-route all
Destination Gateway State
----------- ------- -----
1.1.1.0/24 172.31.1.250 Active
172.16.1.0/24 172.31.1.250 Active
172.31.1.0/24 ManagementEthernet 1/0 Connected
Dell#
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.
PMTD is enabled by default on the switches that support this capability. To enable PMTD to function
correctly, you must enter the ip unreachables command on a VLAN interface to enable the generation of
ICMP unreachable messages. PMTD is supported on all the layer 3 VLAN interfaces. Because all of the Layer 3
interfaces are mapped to the VLAN ID of 4095 when VLAN sub-interfaces are configured on it, it is not
possible to 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 it, 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 452