Understanding Martian Addresses on Junos Devices

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Martian addresses on a Junos device refer to IP addresses that should never appear on the public internet, either because they are not globally unique or because they are reserved for private use only. These addresses are often referred to as "Martian" because they are "alien" or "foreign" to the public internet.

In other words, Martian addresses are IP addresses that are not routable on the internet, and their appearance in the public internet routing table can cause issues and create security risks.

Some examples of Martian addresses include IP addresses in the following ranges:

• 0.0.0.0/8 (for example, 0.0.0.0/32, 0.0.0.0/31, 0.0.0.0/30)
• 127.0.0.0/8 (for example, 127.0.0.1/32)
• 169.254.0.0/16 (for example, 169.254.0.1/32)
• 192.0.2.0/24 (for example, 192.0.2.1/32)
• 198.51.100.0/24 (for example, 198.51.100.1/32)
• 203.0.113.0/24 (for example, 203.0.113.1/32)

These addresses are reserved by the Internet Assigned Numbers Authority (IANA) for private use, testing, and documentation purposes, and should not be used on the public internet.

To prevent Martian addresses from being propagated through the network, Junos devices have a built-in filter that drops traffic from these addresses. Additionally, Junos devices will never install Martian addresses in their routing tables by default, so they cannot be used to route traffic on the public internet.

In summary, Martian addresses on a Junos device are IP addresses that should never appear on the public internet, and their appearance can cause issues and create security risks. They are filtered by Junos devices by default, and are not installed in the routing table.