Creating IP Alias Devices on Different Subnets Behind a Site-to-Site VPN
In this article, we will discuss the process of creating IP alias devices on different subnets behind a site-to-site VPN. Specifically, we will cover the case where one router (Router1) controls the 11.11.11.0/24 subnet, and another router (Router2) controls the 192.168.1.0/24 subnet. We will assume that the tunnel between the two routers is already working correctly.
Background
A site-to-site VPN is a type of VPN that connects two or more networks together over the internet. In this case, we have two networks, each with its own subnet, that we want to connect together. We will use a site-to-site VPN to create a secure tunnel between the two networks, allowing devices on each network to communicate with each other as if they were on the same local network.
Creating IP Alias Devices
Once the site-to-site VPN is established, we can create IP alias devices on each network. An IP alias device is a virtual interface that allows a device to have multiple IP addresses. This can be useful in a variety of situations, such as when we want to run multiple services on a single device, or when we want to test network configurations without affecting production systems.
To create an IP alias device on Router1, which controls the 11.11.11.0/24 subnet, we can use the following commands:
enable
configure terminal
interface vlan 1
ip address 11.11.11.1 255.255.255.0
ip address 10.0.0.1 255.255.255.0 secondary
no shutdown
exit
In this example, we have created a new IP alias device on Router1 with the IP address 10.0.0.1/24. This device is associated with VLAN 1, which is already configured on the router. We have also specified that the new IP address is secondary, meaning that it will only be used if the primary IP address (11.11.11.1/24) is not available.
To create an IP alias device on Router2, which controls the 192.168.1.0/24 subnet, we can use the following commands:
enable
configure terminal
interface vlan 1
ip address 192.168.1.1 255.255.255.0
ip address 10.0.0.2 255.255.255.0 secondary
no shutdown
exit
In this example, we have created a new IP alias device on Router2 with the IP address 10.0.0.2/24. This device is also associated with VLAN 1, which is already configured on the router. We have specified that the new IP address is secondary, meaning that it will only be used if the primary IP address (192.168.1.1/24) is not available.
Testing the Configuration
Once we have created the IP alias devices on both routers, we can test the configuration by pinging one IP alias device from the other. For example, we can log in to Router1 and ping the IP alias device on Router2:
enable
ping 10.0.0.2
If the configuration is correct, we should see reply messages from the IP alias device on Router2. We can also test the configuration by attempting to access services on the IP alias devices from devices on the other network. For example, we could set up a web server on the IP alias device on Router1 and attempt to access it from a device on the 192.168.1.0/24 subnet.
- Site-to-site VPNs allow two or more networks to communicate with each other over the internet.
- IP alias devices allow a device to have multiple IP addresses, which can be useful in a variety of situations.
- To create an IP alias device on a router, we can use the
ip addresscommand to specify the new IP address and associate it with a VLAN. - We can test the configuration by pinging one IP alias device from the other, or by attempting to access services on the IP alias devices from devices on the other network.