H3C Technologies H3C S5560 Series Switches - Manual (Page 33)

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Step Command Remarks
6. Bring up the loopback
interface.
undo shutdown By default, a loopback interface is up.
Configuring a null interface
A null interface is a virtual interface and is always up, but you cannot use it to forward data packets or
configure it with an IP address or link layer protocol. The null interface provides a simpler way to filter
packets than ACL. You can filter undesired traffic by transmitting it to a null interface instead of applying
an ACL. For example, if you specify a null interface as the next hop of a static route to a network segment,
any packets routed to the network segment are dropped.
To configure a null interface:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter null interface view. interface null 0
Interface Null 0 is the default null
interface on the device and cannot
be manually created or removed.
Only one null interface, Null 0, is
supported on the device. The null
interface number is always 0.
3. Set the interface description. description text The default setting is NULL0 Interface.
4. Restore the default settings for
the null interface.
default N/A
Configuring an inloopback interface
An inloopback interface is a virtual interface created by the system, which cannot be configured or
deleted. The physical layer and link layer protocol states of an inloopback interface are always up. All
IP packets sent to an inloopback interface are considered packets sent to the device itself and are not
forwarded.
Displaying and maintaining loopback, null, and
inloopback interfaces
Execute display commands in any view and reset commands in user view.
Task Command
Display information about the specified or all
loopback interfaces.
display interface [ loopback [ interface-number ] ] [ brief
[ description ] ]
display interface [ loopback ] [ brief [ down ] ]