Dual ISP WAN interfaces in the same network

[Miguel Alejandro Callejas Pastor]

Hi everyone,

I am facing a really simple but tricky scenario. My ISP is giving me 2 public IP addresses, both in the same network. They also gave me the default gateway which of course is in the same network too. 

I need both ip addresses fully operational but I realised that I can't have two interfaces (routed interfaces) in the same network segment. I just have one router (a Cisco 2911). A friend told me that I might be able to configure this using VRF but as far as I could read, there is no way to use VRF to accomplish this.

Is there any way to use two (or more) ip addresses to redirect traffic to the same default gateway within the same router?

Thanks!

Miguel

[Peter Paluch · Accepted solution]

Hi Miguel,

If you just want your 2911 to have both public IP addresses configured, you can set one of them as a secondary IP address. Let's assume that 192.0.2.1/29 is your default gateway, and 192.0.2.2/29 and 192.0.2.3/29 are your IP addresses. So to have them both configured, you'd do:

interface Gigabit0/0/0
 ip address 192.0.2.2 255.255.255.248
 ip address 192.0.2.3 255.255.255.248 secondary

And voila - that should do the trick :)

Best regards,
Peter

[Miguel Alejandro Callejas Pastor]

Thanks, this helped me to accomplish the requirement. 

Miguel

[ahmedshoaib]

Hi Miguel,

Just want Little bit more information what you will  achieve after assign 2 public IP address on your Router interfere. By doing you will Don't achieve any thing. 2ND public IP address will be use in meaning full area just like assigned your public server / email gateway and etc.

Thanks & Best regards

[Miguel Alejandro Callejas Pastor]

Hi,

It was a requirement for some developers inside the company. Some traffic from specific applications and hosts should use the second public IP address to reach the internet. 

ACLs and PAT helped a bit, then route maps were helping too. Then it got complicated with tunnels and crypto maps inside so we needed to separate them completely. 

We have tried with the secondary IP address and it was interesting what we could do. In the meanwhile we bought an ASA. 

I appreciate your help!

Miguel