Introduction- ArubaOS supports multiple IP addresses per VLAN and loopback interface. This allows the user to specify any number of secondary IP addresses. Secondary IP address can be used in a variety of situations, such as the
following:
- If an insufficient number of host addresses are available on a particular network segment. Using secondary IP addresses on the routers or access devices allows you to have two logical subnets using one physical subnet
- If the an older network is built using Layer 2 bridges and has no subnetting. Secondary addresses can aid in the transition to a subnetted, router-based network.
- Two subnets of a single network might be otherwise separated by another network. You can create a single network from subnets that are physically separated by another network using a secondary address.
Feature Notes- Important Points to Remember:
- OSPF advertises the secondary IP address in the router LSA but it does not form adjacency on the secondary IP address.
- PIM will not send hello packets on the secondary IP address.
- DHCP servers identify the subnets associated with secondary IP addresses used for allocation.
Configuration Steps- Configuring Secondary IP:
To configure a secondary IP address, use the following command:
(host) (vlan "1") #ip address 1.1.1.1 255.255.255.0 ?
secondary Make this IP address a secondary address
Sample Configuration:
(host) (config) #interface vlan 2
(host) (vlan "2") #ip address 1.1.1.1 255.255.255.0 secondary
Answer- (host) (vlan "2") #show interface vlan 2
VLAN2 is administratively Up, Line protocol is Up
Hardware is CPU Interface, Address is 00:0b:86:6a:1c:c0
Description: 802.1Q VLAN
Internet address is 20.20.20.1, Netmask is 255.255.255.0
Internet address is 1.1.1.1, Netmask is 255.255.255.0 secondary
IPV6 link-local address is fe80::b:8600:26a:1cc0
Global Unicast address(es):
Routing interface is enable, Forwarding mode is enable
Directed broadcast is disabled, BCMC Optimization disabled
Verification- (ArubaS1500-24P) (config) #interface vlan 20
(ArubaS1500-24P) (vlan "20") #ip address 10.1.1.4 255.255.255.0 secondary
(ArubaS1500-24P) (vlan "20") #show ip interface brief
Flags: S - Secondary IP address
Probe: U - Up, D - Down, U/O - Up & Own IP, N/A - Not Applicable
Interface IP Address / IP Netmask Admin Protocol Probe Flags
vlan 1 10.17.169.165 / 255.255.255.0 Up Up N/A
vlan 10 unassigned / unassigned Up Down N/A
vlan 20 20.1.1.2 / 255.255.255.0 Up Up N/A
vlan 20 10.1.1.4 / 255.255.255.0 Up Up N/A S --> S Flag indicate its secondary
gre-tunnel 1 unassigned / unassigned Up Down N/A
Internal Note- Verified and tested in 7.4.0.2 image version.