Networking question (IPv6 adapter downgrading to IPv4 for VPN)

I’ve got my corporate VPN set up not to use the default gateway so that all non-VPN traffic stays routed through my local provider when I’m connected. If I don’t do this, everything is really slow as my traffic has to go halfway across the country and back.

Lately I’ve been having a lot of latency on certain websites (mostly video stuff, youtube, facebook) when I’m connected to the VPN. I thought that traffic was somehow getting routed through the VPN again but when I run a trace I see that when I’m NOT connected, the adapter is using IPv6 addresses, and when I AM connected, it uses IPv4 with a completely different route. If I disconnect the VPN and turn off IPv6 on the adapter, it uses the same IPv4 route as it does when IPv6 is enabled but I’m connected to the VPN, so I know it’s not going through the VPN.

More testing is required, but everything seems much better when I have it configured like this, with IPv6 disabled. Using IPv6 seems quick, but having IPv6 enabled and having the connection downgraded to IPv4 (to be compatible with the VPN, I assume) results in a lot of latency.

Can anyone explain to me what’s going on here?

IPV6 and V4 is not a matter of speed, it’s only a matter of address size. Think of it as the difference between address an envelope to mail with just a street address versus the entire full address with country and ZIP+4. Same letter, just a different format that makes it easier to have more locations addressable.

Now, IPV6 is not widely adopted, so anything using it often needs to be encapsulated in an IPV4 packet to actually get where it needs to go. There’s a few methods of doing this, but all of them are goingt to add overhead, which means it slows down the connection to accommodate the extra translation data. I woulnd’t normally expect it to result in noticable slowness, but it could be the result of a poorly formatted translator somewhere in your connection chain that’s bouncing the encapsulated packets around more.

If it’s working faster to disable v6, by all means leave it disabled. There is no advantage to you to have it on, until the entire internet also adopts it.

I just re-read my OP and I’m not sure it makes any sense. Here’s a summary:

IPv6 ON, VPN OFF = adapter uses IPv6, steronz has fast internet
IPv6 ON, VPN ON = adapter uses IPv4, steronz has slow internet
IPv6 OFF, VPN ON = adapter uses IPv4 (naturally), steronz has fast internet again.

I’m just not sure why. Why does route A-B-C work fine if my adapter is in IPv4 mode natively, but that same route A-B-C work poorly if my adapter is forced to use IPv4 mode for compatibility purposes. FTR, this happens on both my wired and wireless adapters.