By a loopback interface I mean an interface that does not have a receiver system, but instead transmits the sent (and optionally transformed) message back to the sender. In the past I’ve seen only solutions which involved a receiver system with a small dummy server, that responded with the request sent to it. The loopback interface is used to identify the device. While any interface address can be used to determine if the device is online, the loopback address is the preferred method. Whereas interfaces might be removed or addresses changed based on network topology changes, the loopback address never changes.
This section describes how to configure and use user-defined loopback interfaces on the switch.
NOTE: The interface loopback command is not support by HP Switch 2530 (J9772A–J9783A) products. |
By default, each switch has an internal loopback interface (
lo0
) with the IP address 127.0.0.1. This IP address is used only for internal traffic transmitted within the switch and is not used in packet headers in egress traffic sent to network devices.You can configure up to seven other loopback interfaces (
lo1
, lo2
, lo3
, and so on) on the switch to use to transmit network across the network. Each loopback interface can have multiple IP addresses. Routing protocols, such as RIP and OSPF, advertise the configured loopback addresses throughout a network or autonomous system.User-defined loopback addresses provide the following benefits:
- A loopback interface is a virtual interface that is always up and reachable as long as at least one of the IP interfaces on the switch is operational. As a result, a loopback interface is useful for debugging tasks since its IP address can always be pinged if any other switch interface is up.
- You can use a loopback interface to establish a Telnet session, ping the switch, and access the switch through SNMP, SSH, and HTTP (WebAgent).
- A loopback IP address can be used by routing protocols. For example, you can configure the loopback IP address as the router ID used to identify the switch in an OSPF area. Because the loopback interface is always up, you ensure that the switch's router ID remains constant and that the OSPF network is protected from changes caused by downed interfaces.
NOTE: OSPF does not require that you use an IP address as the router ID. OSPF only requires the router ID to be a unique value within the autonomous system (AS). However, if you configure the loopback IP address as the router ID, OSPF can reach the switch if any switch interface is up. (Normally, OSPF automatically configures the router ID with the IP address of a switch interface. The disadvantage is that if the interface goes down, OSPF can no longer ping the switch using the router ID even if other interfaces are operational.) For more information about how to configure a loopback IP address to participate in an OSPF broadcast area, See the section titled '(Optional) Assigning Loopback Addresses to an Area' in the Multicast and Routing Guide. |
NOTE: The interface loopback command is not support by HP Switch 2530 (J9772A–J9783A) products. |
To configure a loopback interface, enter the interface loopback command at the global configuration level of the CLI:
Loopback Interface
Syntax
[no]
interface loopback
<number>
Creates a loopback interface, where<number> is a value from 1 to 7. Use thenoform of the command to remove the loopback interface.
Loopback Interface Hack
Note:You cannot remove the default loopback interface (number 0) with IP address 127.0.0.1.
You can configure up to thirty-two IP addresses on a loopback interface. To configure an IP address for the loopback interface, enter the ip address <ip address> command at the loopback interface configuration level as shown in the following example.
Note that when you configure an IP address for a loopback interface, you do not specify a network mask. The default subnet mask 255.255.255.255 is used.
NOTE:
|
To display the list of loopback interfaces which have been assigned IP addresses, enter the show ip command.
In the show ip command output, information about configured loopback interfaces is displayed below other IP configuration parameters, such as packet TTL and ARP age-out values, and VLAN IP configurations. The following example displays the IP addresses configured for two user-defined loopback interfaces (lo1) and (lo2).
The show ip command output
NOTE: The default loopback interface ( lo0 ) with IP address 127.0.0.1 is not displayed in the show ip command output because it is permanently configured on the switch. To display the default loopback address, enter theshow ip route command as shown in the example below. |
To display the loopback interfaces configured on the switch in a list of IP routing entries displayed according to destination IP address, enter the show ip route command.
The following example displays the configuration of the default loopback interface (lo0) and one user-defined loopback interface (lo2).
The show ip route command output
-->This article describes how to install the Microsoft Loopback Adapter.
Original product version: Windows Server 2003
Original KB number: 842561
Original KB number: 842561
Introduction
Purpose Of Loopback Interface
This article describes how to install the Microsoft Loopback Adapter in Microsoft Windows Server 2003. You can install the adapter by using a command prompt or by using the Hardware Wizard.
More information
Method 1
To quickly install the Microsoft Loopback Adapter in Microsoft Windows Server 2003, use the DevCon utility at a command prompt. To download and to run the DevCon utility, follow these steps:
- Download the DevCon compressed file, and then extract the files:
- Visit the following Microsoft Web site:
Windows Device Console (Devcon.exe) - Save the Devcon.exe file to a folder on your computer, and then open the folder.
- Double-click Devcon.exe. A WinZip Self-Extractor dialog box appears.
- In the Unzip to path box, type the folder where you want to unzip the files, and then click Unzip.
- Click OK, and then Close to complete the unzip process.
- Install the Microsoft Loopback Adapter:
- At a command prompt, change directory to the folder where you extracted the DevCon files.
- Change directory to the i386 folder.
- Type devcon.exe install %windir%infnetloop.inf *msloop, and then press ENTER. You see output that is similar as:
Device node created. Install is complete when drivers are updated...
Updating drivers for *msloop from C:WINDOWSinfnetloop.inf.
Drivers updated successfully. - Close the command prompt.
- Click Start, click Control Panel, and then click Network Connections to verify that the Microsoft Loopback Adapter has been installed.
Method 2
To install the Microsoft Loopback Adapter by using the Hardware Wizard, follow these steps:
- In Control Panel, double-click Add Hardware, and then clickNext
- Click Yes, I have already connected the hardware, and then clickNext.
- At the bottom of the Installed hardware list, click Add a new hardware device, and then click Next.
- Click Install the hardware that I manually select from a list, and then click Next
- In the Common hardware types list, click Network adapters, and then click Next.
- In the Manufacturers list box, click Microsoft.
- In the Network Adapter list box, click Microsoft Loopback Adapter, and then click Next.
- Click Next to start installing the drivers for your hardware.
- Click Finish.
- Click Start, click Settings, and then click Network Connections to verify that the Microsoft Loopback Adapter has been installed.
References
For additional information about the DevCon utility, click the following article number to view the article in the Microsoft Knowledge Base:
311272 DevCon command-line utility alternative to Device Manager