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The system installs a next hop that is on the directly connected subnet of current IP address on the interface (for example, if
interface tengig 0/0 is on 172.31.5.0 subnet, the system installs the static route).
The system 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. For example, if tengig 0/0 has ip address on subnet 2.2.2.0 and if 172.31.5.43 recursively
resolves to 2.2.2.0, the system installs the static route.
● When the interface goes down, the system withdraws the route.
● When the interface comes up, the system re-installs the route.
● When the recursive resolution is “broken,” the system withdraws the route.
● When the recursive resolution is satisfied, the system 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.
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.
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.
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IPv4 Routing