Brocade Communications Systems ICX 7250 series, Configuration Manual

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Disabling ICMP destination unreachable messages
By default, when a Brocade device receives an IP packet that the device cannot deliver, the device sends an ICMP Unreachable message
back to the host that sent the packet. You can selectively disable a Brocade device response to the following types of ICMP Unreachable
messages:
• Host - The destination network or subnet of the packet is directly connected to the Brocade device, but the host specified in the
destination IP address of the packet is not on the network.
• Protocol - The TCP or UDP protocol on the destination host is not running. This message is different from the Port
Unreachable message, which indicates that the protocol is running on the host but the requested protocol port is unavailable.
• Administration - The packet was dropped by the Brocade device due to a filter or ACL configured on the device.
• Fragmentation-needed - The packet has the Do not Fragment bit set in the IP Flag field, but the Brocade device cannot
forward the packet without fragmenting it.
• Port - The destination host does not have the destination TCP or UDP port specified in the packet. In this case, the host sends
the ICMP Port Unreachable message to the Brocade device, which in turn sends the message to the host that sent the packet.
• Source-route-fail - The device received a source-routed packet but cannot locate the next-hop IP address indicated in the
packet Source-Route option.
You can disable the Brocade device from sending these types of ICMP messages on an individual basis. To do so, use the following CLI
method.
NOTE
Disabling an ICMP Unreachable message type does not change the Brocade device ability to forward packets. Disabling ICMP
Unreachable messages prevents the device from generating or forwarding the Unreachable messages.
To disable all ICMP Unreachable messages, enter the no ip icmp unreachable command.
device(config)# no ip icmp unreachable
Syntax: [no] ip icmp unreachable { host | protocol | administration | fragmentation-needed | port | source-route-fail }
• If you enter the command without specifying a message type (as in the example above), all types of ICMP Unreachable
messages listed above are disabled. If you want to disable only specific types of ICMP Unreachable messages, you can specify
the message type. To disable more than one type of ICMP message, enter the
no ip icmp unreachable command for each
messages type.
• The host parameter disables ICMP Host Unreachable messages.
• The protocol parameter disables ICMP Protocol Unreachable messages.
• The administration parameter disables ICMP Unreachable (caused by Administration action) messages.
• The fragmentation-needed parameter disables ICMP Fragmentation-Needed But Do not-Fragment Bit Set messages.
• The port parameter disables ICMP Port Unreachable messages.
• The source-route-fail parameter disables ICMP Unreachable (caused by Source-Route-Failure) messages.
To disable ICMP Host Unreachable messages but leave the other types of ICMP Unreachable messages enabled, enter the following
commands instead of the command shown above.
device(config)# no ip icmp unreachable host
If you have disabled all ICMP Unreachable message types but you want to re-enable certain types, for example ICMP Host Unreachable
messages, you can do so by entering the following command.
device(config)# ip icmp unreachable host
Configuring IP parameters - Layer 3 switches
Brocade FastIron Layer 3 Routing Configuration Guide
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