Wired Intelligent Edge (Campus Switching and Routing)

Environment : This article applies to all Aruba Mobility switches and code versions.

1. We cannot configure an IP address from existing vlan subnet on a loopback interface in Aruba Mobility Switches.
This is different from Aruba Controllers where we can configure the addresses from existing subnet on a loopback interface.:

(ArubaS2500-24P) (config) #interface vlan 1
(ArubaS2500-24P) (vlan "1") #ip address 10.1.1.1 255.255.255.0
(ArubaS2500-24P) (vlan "1") #exit
(ArubaS2500-24P) (config) #interface loopback 0
(ArubaS2500-24P) (loopback "0") #ip address 10.1.1.2
Error: IP address conflict with vlan 1

(ArubaS2500-24P) (loopback "0") #ip address 100.1.1.2
(ArubaS2500-24P) (loopback "0") #

Verify:

(ArubaS2500-24P) (loopback "0") #show ip interface brief

Flags: S - Secondary IP address
Interface                   IP Address / IP Netmask        Admin   Protocol   Flags
vlan 1                        10.1.1.1 / 255.255.255.0     Up      Up
loopback 0                 100.1.1.2 / 255.255.255.255   Up      Up
mgmt                        unassigned / unassigned        Up      Down

2. We can however, have ip addresses from the same subnet if it exists only on one of the loopback interface of the Switch:

(ArubaS2500-24P) (config) #interface vlan 1
(ArubaS2500-24P) (vlan "1") #ip address 10.1.1.1 255.255.255.0
(ArubaS2500-24P) (vlan "1") #ip address 100.1.1.1 255.255.255.0 secondary
(ArubaS2500-24P) (vlan "1") #interface loopback 0
(ArubaS2500-24P) (loopback "0") #ip address 10.1.2.1
(ArubaS2500-24P) (loopback "0") #
(ArubaS2500-24P) (loopback "0") #interface loopback 1
(ArubaS2500-24P) (loopback "1") #ip address 10.1.2.2
(ArubaS2500-24P) (loopback "1") #ip address 10.1.2.3 secondary
(ArubaS2500-24P) (loopback "1") #exit


3. Unlike for Vlan interface secondary addresses, show ip interface brief command will only show the primary IP address on a loopback interface:

(ArubaS2500-24P) (config) #show ip interface brief
Flags: S - Secondary IP address
Interface                   IP Address / IP Netmask        Admin   Protocol   Flags
vlan 1                        10.1.1.1 / 255.255.255.0     Up      Up
vlan 1                       100.1.1.1 / 255.255.255.0     Up      Up         S
loopback 0                    10.1.2.1 / 255.255.255.255   Up      Up
loopback 1                    10.1.2.2 / 255.255.255.255   Up      Up
mgmt                        unassigned / unassigned        Up      Down


4. To view all the IP addresses configured on a loopback:

(ArubaS2500-24P) (config) #show interface loopback 0
loopback 0 is administratively Up, Line protocol is Up
Hardware is Loopback
Description: Loopback
Internet address is 10.1.2.1, Netmask is 255.255.255.255
Interface index: 100663296
MTU 1514 bytes

(ArubaS2500-24P) (config) #show interface loopback 1
loopback 1 is administratively Up, Line protocol is Up
Hardware is Loopback
Description: Loopback
Internet address is 10.1.2.2, Netmask is 255.255.255.255
Internet address is 10.1.2.3, Netmask is 255.255.255.255 secondary
Interface index: 100663297
MTU 1514 bytes