Additional IP Addresses on Cisco Router Interface

[LinuxAdmin]

Hello Community,

I am a newbie trying to get my hands on couple of Routers. I have been going through lot of docs and videos but kinda stuck with these 2 questions.

1. Is it possible to use 3 Ethernet ports of Cisco Router 4331? The requirement is to connect 2 Network switches from different Networks and another Server. So in all 3 Networks need to be connected to this router. But it seems I am failing short of 1 Ethernet port. Please suggest.

2. Can we configure multiple IP Addresses on a single Ethernetport of the Router. E.g. Can Gigabitetherner 0/0/1 Port have 2 IP Addresses of same network? 1.176.86.1 and 1.176.86.10 Something like ip alias? It is specific requirement in which these 2 IPs are defined as gatway on 2 different Hosts. So if one of the hosts is down, the other should continue to work using another IP. 

I tried to look for help and found some reference of ip alias command. But it does not work on my Router 4331. It says invalid command. There was another hint to use keyword secondary as shown below. But that did not work as well.

ip address X.X.X.X  255.255.255.0  secondary

  So kindly suggest any hints if it is at all possible.

Thanx in advance.

Regards.

[balaji.bandi]

1 - yes you can use 3 interface to connect to different device (until you are concerned any interface let us know.

2- this is not possible of overlap ip address range as seconday, you can do subnet of the ip range and can be used.

Hope this make sense ? if our understanding not correct pleae clarify ?

[LinuxAdmin]

1 - yes you can use 3 interface to connect to different device (until you are concerned any interface let us know.

I think I did not explain the problem correctly. The problem is there are only 2 Ethernet Ports available on Cisco 4331 Router. The other 2 are SFP Ports. So thats the whole problem.

2- this is not possible of overlap ip address range as seconday, you can do subnet of the ip range and can be used.

Can you please elaborate. We wish to have 2 IPs to single Interface. (a. 10.10.10.1 and b. 10.10.10.2)   What command to be used for this?

[balaji.bandi]

1- #show inventory  (show you what module)

if you have Cisco 2-Port Gigabit Ethernet WAN Network Interface Module (NIM-2GE-CU-SFP) (Figure 1) - you can use 2 ports at a time, you can use 3 porsts here..

2. as mentioned that is not possible. instead :

you can do subnet 10.10.10.0/25 10.10.10.128/25

you can bind first interface 10.10.10.1/25 and other one 10.10.10.129/25 (is this works ?)

[LinuxAdmin]

1. SFP Module ist the only thing that seems to be possible if we have to use 3 Ports. Thanks for confirmation.

2. In the Cisco documentation there is something called (see below) which can be used to display IP aliases Tabel. So i thought this should be possible. But unfortunately i did not find any such example. And sorry but the idea of subnet does not really work for us. 

#show ip aliases

[balaji.bandi]

2-  not sure what is the use case here for 2 IP address in same interface ? why they can not have same gateway ?

[LinuxAdmin]

Your question is correct, ideally it does not. But we wish to have a configuration as if there are 2 Routers each connecting individual Hosts. So in case 1 of the routers is down , the connection should still take place over the other router.  This setup we wish to test using 1 Router and having the single interface with 2 IP Addresses.

[balaji.bandi]

#the solution you looking not going to be achivable. since you are allocating same IP address (if the router go down) both the interface go down.

if that is very critical, then you need to HsRP in place with dual uplink. with VIP IP as gateway for Device.

[LinuxAdmin]

I do understand your point. But this is the test-scenario which we want to only simulate. In the real scenario, we will be using 2 separate routers for 2 individual hosts. This is only simulation which we wish to test.

The real question is, can we assign same IP to same Interface on Router? Please just let me know if this is technically possible? Does not matter how,  using ip alias or  secondary or using any method. I just want to know if it is at all possible.

[balaji.bandi]

You can not simulate the scenario, and you like to test, use any simulator labs and test the feature.

The real question is, can we assign same IP to same Interface on Router? Please just let me know if this is technically possible? Does not matter how,  using ip alias or  secondary or using any method. I just want to know if it is at all possible.

NO

[LinuxAdmin]

Thanks for the reply. But I have found couple of links on cisco.com website which show that it is possible. It is just that the command "secondary" is not working on Cisco packet tracer simulator.

https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-1/addr_serv/configuration/guide/ipaddr_cg41a9k_chapter8.html#task_1026544

https://community.cisco.com/t5/other-network-architecture/any-limit-to-number-of-secondary-ip-addresses/td-p/462783https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-1/addr_serv/configuration/guide/ipaddr_cg41a9k_chapter8.html#ta...