A network engineer configures a site-to-site VPN with a colleague. During testing, the engineer discovers that only phase 1 is up, and application traffic cannot pass. Which configuration parameter…

Mismatched hash algorithms (e.g., MD5 vs. SHA) would prevent Phase 1 from coming up entirely, not just cause a Phase 2 or traffic issue after Phase 1 is established.

An incorrect peer IP address would prevent Phase 1 from initiating or completing, as the devices wouldn't be able to find each other.

In a site-to-site VPN, if Phase 1 (IKE SA) is up but Phase 2 (IPsec SA) cannot establish, or traffic is not passing, a common issue is mismatched or incorrectly defined encryption domains (interesting traffic/proxy IDs). The encryption domain defines which subnets or hosts are allowed to pass through the VPN tunnel, and both ends must agree on this definition for traffic to be encrypted and forwarded.

A mismatched preshared key would prevent Phase 1 from completing authentication, meaning Phase 1 would not be up.