3com MSR 20-20 참조 매뉴얼

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The primary and secondary IP addresses can be located in the same network 
segment.

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Before removing the primary IP address, remove all secondary IP addresses.

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You can assign a secondary IP address only when the interface is not 
configured to borrow an IP address through IP unnumbered or obtain one 
through BOOTP, DHCP, or PPP negotiation.

display ip interface.

Assign Ethernet1/0 a primary IP address and a secondary IP address, with the 
subnet masks both being 255.255.255.0.

<Sysname> system-view

[Sysname] interface ethernet 1/0

[Sysname-Ethernet1/0] ip address 129.102.0.1 255.255.255.0

[Sysname-Ethernet1/0] ip address 202.38.160.1 255.255.255.0 sub 

ip address unnumbered interface interface-type interface-number

Interface view

interface interface-type interface-number: Specifies an interface from which the 
current interface can borrow an IP address.

Use the ip address unnumbered command to configure the current interface 
as IP unnumbered to borrow an IP address from another interface.

Use the undo ip address unnumbered command to disable IP unnumbered on 
the interface.

By default, the interface does not borrow IP addresses from other interfaces.

# Configure PPP-encapsulated interface Serial 2/2 to borrow IP address from 
interface Ethernet 1/0.

<Sysname> system-view

[Sysname] interface serial 2/2

[Sysname-Serial2/2] ip address unnumbered interface ethernet 1/0