Service Manual

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Dell Networking OS installs a next hop that is on the directly connected subnet of current IP address on the interface (for example, if
interface GigabitEthernet 1/1 is on 172.31.5.0 subnet, Dell Networking OS installs the static route).
Dell 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 congured subnet. For example, if gig 0/0 has ip address on subnet 2.2.2.0 and if 172.31.5.43 recursively
resolves to 2.2.2.0, Dell Networking OS installs the static route.
• When the interface goes down, Dell Networking OS withdraws the route.
• When the interface comes up, Dell Networking OS re-installs the route.
• When the recursive resolution is “broken,” Dell Networking OS withdraws the route.
• When the recursive resolution is satised, Dell Networking OS re-installs the route.
Congure Static Routes for the Management Interface
When an IP address that a protocol uses and a static management route exists for the same prex, the protocol route takes
precedence over the static management route.
To congure 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}
Example of the show ip route static Command
To view the congured static routes for the management port, use the show ip management-route command in EXEC
privilege mode.
Dell#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
This functionality is supported on the platform.
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 dierent for various types of trac sent
from one host to the same endpoint.
Path MTU discovery (PMTD) identies 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
IPv4 Routing
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