> Source: [sk157074](https://support.checkpoint.com/results/sk/sk157074)

# sk157074 - Decrypted Site-to-Site VPN traffic dropped for anti-spoofing

| Property | Value |
|----------|-------|
| Solution ID | sk157074 |
| Date Created | 2019-06-28 |
| Last Modified | 2020-10-20 |
| Technical Level | Advanced |

## Symptoms

- * Decrypted Site-to-Site VPN traffic dropped for anti-spoofing.
* IKE and IPSEC SA is successful (Phase 1 and Phase 2 SAs created successfully)
* Some or all VPN site-to-site traffic not reaching destination.
* *fw ctl zdebug + drop* indicates the problematic traffic is dropped for "anti spoofing"
* External (Internet) interface has anti-spoofing "Prevent" action enabled.

## Cause

If the gateway has an interface topology configured which "leads to" a network range, or a group, that overlaps with the remote VPN peer's encryption domain, the decrypted inbound traffic will be interpreted as being on the 'wrong' interface and dropped for anti-spoofing.

Example: Interface eth1 "leads to" 10.0.0.0/8

![](https://sc1.checkpoint.com/sc/SolutionsStatics/NEW_SK_NOID1561740637862/leadsto1906281011.png)

If the VPN peer encryption domain should happen to overlap (e.g. if the peer encryption domain were 10.100.0.0/24), the decrypted traffic from that peer would be dropped on the external interface for anti-spoofing, as the gateway expects the traffic (10.100.0.0/24 in our example) only from eth1 (which is internal).

## Solution

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