Tuesday, November 6, 2018

Juniper SRX TIFU

Before you start reading this I should clarify that I'm not a Juniper expert, but I'm pretty decent at most network stuff and I am pretty familiar with IPsec and have set up a large number of tunnels on Linux and other firewalls (Watchguard, Sophos UTM etc).

We have a client we deployed an SRX300 to for an office environment on a 100/100 connection.

They have an Azure Active Directory Domain Services configuration and after some research I configured an IPSEC connection from the Juniper SRX to an Azure Virtual Network Gateway.

I based my configuration on the SRX route based example here: https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-about-vpn-devices#devicetable

I enabled VPN Monitor functionality which was described as monitoring the connection (when it did not detect traffic) for drops and re-establishing/re-keying.

Here is where the tifu comes in.

I assumed VPN Monitor was a smarted Dead Peer Detection replacement, it is not.

DPD operates on IKE (Phase 1) and re-keys it as required.

VPN Monitor does a similar job more intelligently, but operates only on Phase 2.

It took me about 8-10 hours of testing other stuff, checking azure, etc, etc to figure it out.

Hopefully this helps someone else avoid this particular pain.



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