Community discussions

MikroTik App
 
1soproni
just joined
Topic Author
Posts: 4
Joined: Tue Dec 04, 2018 4:29 pm

Openvpn ipv4 server ipv6 client

Wed Sep 08, 2021 3:23 pm

Hi there,

My router have an ipv4 address. If my client (cellphone) get ipv4 address from the ISP the ovpn works well.
If my client get an ipv6 address (second SIM) then the tunnel can establish (I can see public ipv4 client address on the router), echo requests from the client reach the server but cannot reply to them (tcpdump tells "unreachable")

[root@xyz ~]# tcpdump -i eth0 icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
13:28:49.691972 IP 172.16.253.6 > xyz.abc.de: ICMP echo request, id 615, seq 1, length 64
13:28:49.692016 IP xyz.abc.de > 172.16.253.6: ICMP xyz.abc.de protocol 1 port 48194 unreachable, length 92

If the VPN tunnel established why can't traffic goes through?
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11383
Joined: Thu Mar 03, 2016 10:23 pm

Re: Openvpn ipv4 server ipv6 client

Wed Sep 08, 2021 6:11 pm

The way you explained it seems that MNO (ISP of second SIM) is running some sort of 6to4 gateway. And that is by no means transparent (there are simply not enough IPv4 addresses to cover a single /64 prefix, let alone whole IPv6 address space). Which means it is similar to CGNAT. And your tcpdump shows ping session, not VPN traffic, so it is not indicative.
 
1soproni
just joined
Topic Author
Posts: 4
Joined: Tue Dec 04, 2018 4:29 pm

Re: Openvpn ipv4 server ipv6 client

Wed Sep 08, 2021 7:43 pm

And your tcpdump shows ping session, not VPN traffic, so it is not indicative.
I don't understand your last sentence.
Situation:
Server (IPv4) - Router (IPv4) - Phone (IPv6)
Ovpn session established between the router and the phone. Tcpdump runs on the server. I'm start the ping from the phone. I can see the echo requests on the server and replies cannot go back to the phone :(
Why tcpdump is not indicative?

Who is online

Users browsing this forum: akakua, ItchyAnkle, Lumpy, menyarito and 89 guests