IP Unnumbered theory
If you want go deep and learn all about the IP Unnumbered you can always refer to Cisco’s technical documentation, for this particular subject you may want to take a look at the one available at the following link:
But, to make a long story short, basically, an IP Unnumbered is just a sort of borrowed/shared IP address that can be assigned just referring to the interface which will share its IP Address, or you can also refer to the interface VLAN you want to use.
vgw#show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 192.168.1.102 YES NVRAM up up
Service-Engine0/1 unassigned YES unset administratively down down
GigabitEthernet0/1 172.16.1.102 YES NVRAM up up
GigabitEthernet3/0 unassigned YES unset administratively down downIn our example we are going to use the interface GigabitEthernet0/1, line number 5(five) of the above CLI output.
Why interface GigabitEthernet0/1 ?
Well, in our particular case the interface GigabitEthernet0/1 is connecting us to the LAN, you can always use CDP to confirm that.
vgw#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
D - Remote, C - CVTA, M - Two-port Mac Relay
Device ID Local Intrfce Holdtme Capability Platform Port ID
Switch Gig 0/1 126 S I WS-C3750- Gig 1/0/2
vgw#As you can see with “show cdp neighbors” the interface Gig 0/1 is connected to the Cisco switch WS-C3750 on the switch’s interface Gig 1/0/2.
Please notice that we are not configuring our CUE for production yet, what we are doing instead is to just familiarize ourselves with this device and the way we can get as much information about it without having to go over a typical VoIP configuration that includes VLAN and of course the proper integration of our CUE either with CUCM or CME.
For that we must have a few extension numbers already designated as triggers for Voice Mail, AutoAttendant, Admin via Telephone (AVT), Message Waiting Indicator (MWI) ON and OFF, and a few other considerations like dial-peers, users and theirs voice mail profiles, all of that is out of the scope for this LAB at this moment.
Be patient, we’ll configure CUE for production later in our series of articles.
The image perfectly shows our current situation, just a router and a switch isolated and with the minimum configuration that will allow us to play a little bit around while also learn about the CUE and its particular way of configuration.
Assigning the Unnumbered IP
Now that we we know the reason why we are going to use the interface Gig 0/1 to borrow its IP address let’s do it.
vgw#
vgw#conf t
Enter configuration commands, one per line. End with CNTL/Z.
vgw(config)#interface Service-Engine0/1
vgw(config-if)#ip unnumbered GigabitEthernet0/1
vgw(config-if)#^Z
vgw#How does it look so far?
vgw#show running-config interface Service-Engine0/1
Building configuration...
Current configuration : 98 bytes
!
interface Service-Engine0/1
ip unnumbered GigabitEthernet0/1
no ip route-cache
shutdown
end
vgw#The next step also inside the interface Service-Engine0/1 is to assign an IP address for CUE itself (in our LAB just the next available IP in the same subnet) and also the Default Gateway, see below:
vgw#conf t
Enter configuration commands, one per line. End with CNTL/Z.
vgw(config)#interface Service-Engine0/1
vgw(config-if)#service-module ip address 172.16.1.103 255.255.255.0
vgw(config-if)#service-module ip default-gateway 172.16.1.1
vgw(config-if)#exit
vgw(config)#exit
vgw#How does it finally look?
vgw#show running-config interface Service-Engine0/1
Building configuration...
Current configuration : 198 bytes
!
interface Service-Engine0/1
ip unnumbered GigabitEthernet0/1
no ip route-cache
shutdown
service-module ip address 172.16.1.103 255.255.255.0
service-module ip default-gateway 172.16.1.1
end
vgw#Enabling the interface
Now that the IP Addressing has been done we just need to enable the interface using the CLI command “no shutdown”.
vgw#conf t
Enter configuration commands, one per line. End with CNTL/Z.
vgw(config)#interface Service-Engine0/1
vgw(config-if)#no shutdown
vgw(config-if)#^Z
vgw#Let’s check with “show ip interface brief” once again to see the changes completed so far:
vgw#show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 192.168.1.102 YES NVRAM up up
Service-Engine0/1 172.16.1.102 YES unset up up
GigabitEthernet0/1 172.16.1.102 YES NVRAM up up
GigabitEthernet3/0 unassigned YES unset administratively down down
vgw#Looking at lines number 4 and number 5 you can confirm that we in fact now have one IP address being “borrowed” or if you want “shared”, well done! mission accomplished.
Where to go from here?
Because we did also assign an IP address to CUE, now we can move forward and access for the very first time to CUE.