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I know that both are loopback IPs, but they have another ip mask.

What's the difference between them? Can they be used interchangeably?


IPv4 routes
Active routes:
Destination               Mask          Gateway        Interface Metric     26
[...]         On-link    306         On-link    306
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3 Answers 3

up vote 20 down vote accepted

No. You cannot use them both. And they are not both loopback adresses. is a loopback address is a loopback address is a loopback address and so on is a network address. Together with mask it gives you a hint that whole class A of addresses starting with 127.*.*.* will contain loopback addresses.

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thanks for explaining this to me – Disa Mar 30 '13 at 11:16
@mnmnc, Why is the mask necessary? Isn't it standard that 127.*.*.* will contain loopback addresses? – Pacerier Jul 23 at 14:03 is the network address (with netmask or is a host address in that network.

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thanks for your answer – Disa Mar 30 '13 at 11:18
True. with mask could theoretically also work. In praxis that is a very bad idea. since old software used to use the lowest address in a range as broadcast address. – Hennes Mar 30 '13 at 11:29

What is shown in the screenshot is a routing table from a computer. The routing table is just a "roadmap" that tells a computer/router where to go to get to other devices on the network.

In some ways this is similar to how we navigate in real life.

The first column provides the list of known destinations (where can I go) and the second column indicates how specific the destination (I can go to Canada or I can go to Uncle John's house in Canada). Without getting into great detail, the "higher" the mask value, the more specific the destination. So a value of covers going to any device and a value of specifies an individual device.

The third column specifies where traffic should go next to get to the destination (if you are going to Canada, you need to start by getting on Main Street) and the fourth column indicates which path out of the device should be used to get to the destination (from home you may only have your driveway but from the Walmart parking lot you may have several "exits" to choose from).

Finally, the metric gives the computer a way to choose the best path if there are multiple routes to the destination (you can go out either the north or east exit from the parking lot to get to Canada, but the east one is a faster).

So to answer the original question, no you can't use and interchangeably. The difference shown here is that there exists two routes - a general route to any device using 127.x.y.z and a very specific route to host (which is in, both of which use the interface.

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Your last paragraph states that there is a difference. But if we leave out the "specific route" (line, wouldn't traffic to then utilize the "generic route" (line and end up in the same place since both uses the interface? – Pacerier Jul 23 at 14:08

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