New L2L vpn, how does 1 point first find the remote public address?

[MicJameson1]

New L2L vpn, how does 1 point first find the remote public address,?

The 2 public endpoints must find eachother over the www, public IP addresses are assigned to new www endpoints all the time.

So, how does a new route establish in the first place?

Thank you.

[Rob Ingram]

@MicJameson1 I am not really sure I understand of your question, so a guess.....

Are you referring to ASA/FTD/router with a dynamic public IP address? Therefore you do not know the public IP address to peer with?

Assuming you have 1 static IP address on the hub side, the spoke sides can have a dynamic IP address - you would create a dynamic crypto map or from ASA 9.19 (FTD 7.3) you can use a dVTI. Or if using a router use DMVPN or FlexVPN.

[MicJameson1]

My question is simple-- Our organization ads and removes public IP addresses all the time. How does a vendor gain knowledge of a route to our newly assigned IP address location?

At the highest level, does the ISP actively discover new endpoints, and calculate a route through a routing protocol, then send this route through the www routing tables, so that a vendor will gain connectivity to my enterprise new public ip-address because it simply has a default gateway with an always-updating www routing table?

This is relevant knowledge when troubleshooting VPNs refusing to turn-on.

Thank you.

[Rob Ingram · Accepted solution]

@MicJameson1 any new network would need to be advertised using a dynamic routing protocol, the other devices would route out via their default route and communicate with the new IP network.

Routing is the basic requirement to establish a VPN, so you'd use traceroute determine path and ping to determine reachability of the peer when troubleshooting.