100% Packet loss

In this case I have two moniotors set up, one on IPv4 and the other on IPv6 for a BT Business line. Both are working fine when connected through the fixed line FTTC connection.

When the fixed line fails the modem/hub fails over to a 4G connection but maintains the same IPv4 address, IPv6 is then unavailable across teh EE network.

However, BQM shows a 100% packet loss even though te IP is valid and checking with "Whats my IP" confirms the correct v4 address.

WHY?

Can other external sources ping the IPv4 address when it failover mode

Will need to check - although speedtest.net sees the correct IP as does teh "Whats my IP" tool - surely these must both be looking back at the modem/hub.

Neither look at the hub itself - when you access any site it passes your IP in the request so that is how they know the source IP address. They aren't contacting your router to find out.

If you google for websites that have ping tools then you can ping the router from those when it is in fail over mode and see if they get a response.

EDIT : Also, a thought. The Internet stores the route to IP addresses in caches on the routers/switches. When you are going out in failover you are building a new route to the destination so it works fine. However, the route from an external service coming in would be cached so it is possible it would take time for the route to rebuild?

Edited by ian72 (Tue 11-Feb-20 13:50:55)

In reply to a post by ian72:

Neither look at the hub itself - when you access any site it passes your IP in the request so that is how they know the source IP address. They aren't contacting your router to find out.

Agreed, years ago I use to think that that the router cached the internal IP and Port of the source and when it got traffic back the router knew where to return it.

But in fact the source IP (PC) and destination IP (Server) get put into a packet and the MAC Address of the source (PC) and router / gateway gets put into a network frame along with the packet and that gets sent out.

One thing to note is that each gateway the frame goes through will change the destination MAC.

Well something on those lines.

Paul