There is some difference in how lo and dummy are used, but that is the magic 127.0.0.2 stuff that is not important to the question. The same is true for dummy, and the same is true for lo.īut if you haven't observed this, you can use the less advanced explanation. It is possible to verify this with tcpdump or the packet counters in ip -s link. Loopback addresses range from 127.0.0.0. When you ping the IP address of your computer's ethernet or wifi interface, it works without sending anything over that interface. A loopback address is a reserved IP address that sends the outgoing signal back to the computer running the program. (You can play with ip link add type dummy). But there is no need to care unless you are exploiting that "feature" of the legacy version of Internet Protocol, or you are developing the kernel.Ī more advanced way to think of lo is that it does not need to do anything, just like the dummy interface. This is at least clear when you look at the strange fact that ping 127.0.0.2 works, but you cannot see the address 127.0.0.2 in ip -4 addr. In reality the implementation details are not the same. You can think of lo like a veth pair, except there is only one end. They are designed to communicate with containers: one end of the veth pair can be moved into a container. But in the two examples, I don't see that meaning happening, but just the same thing as non-loop back IP addresses.Ī veth pair is a pair of ethernet devices with a cable between them. "loopback" is supposed to mean "a message or signal ends up (or loops) back to where it started" ( ). When I type in browser's address bar and hit return, it works just like typing any other URL.When I type ssh localhost, it works just like ssh with any other IP address.How is that different from a regular scenario?Ĭould you use some commands to show the loopback scenario and the regular one? What are the source and destination in the loopback scenario? It had been received from another device. Simply and immediately passed back up the network software stack as if Īny traffic that a computer program sends to a loopback IP address is Ip ip-prefix prefix10.0.0.1 index 10 deny 10.0.0.1 32 greater-equal 32 less-equal 32 ip ip-prefix prefix10.0.0.1 index 20 permit 0.0.0.I have some difficulty to picture a diagram for the meaning of loopback. Route-policy import_isis_2 permit node 10 apply tag 200 Route-policy import_isis_2 deny node 5 if-match tag 100 Route-policy import_isis_1 permit node 10 apply tag 100 Type interface loopback where is any free interface number on your router. Route-policy import_isis_1 deny node 5 if-match tag 200 However, the tag value specified in the route-policy import_isis_2 deny node 5 configuration on DeviceD for matching is not 100. In this example, however, the tag value is incorrectly set to 300.Ī routing policy is used in IS-IS 2 on DeviceE to import routes from IS-IS 1, and a tag value of 100 is applied to matched routes. Therefore, the tag value in the route-policy import_isis_2 deny node 5 configuration should be set to 100 for matching. It is expected that IS-IS 1 on DeviceD no longer imports a route with a tag value of 100 from IS-IS 2. You can then click on the results to find out more about that IP Address. If you type in an IP address, we will attempt to locate a dns PTR record for that IP address. Import-route isis 1 inherit-cost route-policy import_isis_1Ī routing policy is specified when IS-IS 1 imports routes from IS-IS 2, but the policy configuration is incorrect. Blacklists DMARC Diagnostics Email Health DNS Lookup Analyze Headers All Tools Reverse Lookup IP Address ABOUT REVERSE LOOKUP The Reverse Lookup tool will do a reverse IP lookup. Import-route isis 2 inherit-cost route-policy import_isis_2 Route-policy import_isis_2 permit node 10 Route-policy import_isis_2 deny node 5 if-match tag 300 Route-policy import_isis_1 permit node 10 No routing policy is configured when IS-IS 2 imports routes from IS-IS 1. No routing policy is configured when IS-IS 1 imports routes from IS-IS 2.
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