> Source: [sk183570](https://support.checkpoint.com/results/sk/sk183570)

# sk183570 - "Cannot calculate IP based on network topology, because some network interfaces are defined by routing" error when "Calculate topology automatically based on routing information" is enabled on a VSX Gateway

| Property | Value |
|----------|-------|
| Solution ID | sk183570 |
| Date Created | 2025-07-07 |
| Last Modified | 2025-07-08 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R81.20 |
| OS | Gaia |

## Symptoms

- When configuring Link Selection in SmartConsole with the option **Calculate IP based on network topology** , and the checkbox **Calculate topology automatically based on routing information** is selected, this error appears:

`Cannot calculate IP based on network topology, because some network interfaces are defined by routing.`
![Error window pop-up](https://sc1.checkpoint.com/sc/SolutionsStatics/NEW_SK_NOID1749819502582/Screenshot_for_sk202506131558121.png)

## Cause

This error occurs because Link Selection requires a static and clearly defined IP topology to determine which interface IP to use when building VPN tunnels or handling external traffic.

If **calculate topology automatically based on routing information** is selected, the IP address for some interfaces cannot be determined. As a result, Link Selection cannot reliably identify the correct source IP, and the configuration fails.

## Solution

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