Connection issues

[bjo]

Hi,

since yesterday I'm using a HE-tunnel again and get some connection issues to my KVM-server from time to time. The server has native IPv6. At the moment, I'm trying to send a mail via submission, the connection just hangs. Also ssh-connections are not possible. No ip6tables are set on the server.

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14:04:36.257400 IP6 (hlim 64, next-header TCP (6) payload length: 101) mactra.nord-west.net.submission > mytilus.ipv6.nord-west.net.47200: Flags [P.], cksum 0xc137 (incorrect -> 0xb921), seq 3963:4032, ack 837, win 505, options [nop,nop,TS val 118217597 ecr 5842996], length 69
14:04:36.305516 IP6 (hlim 55, next-header TCP (6) payload length: 138) mytilus.ipv6.nord-west.net.47200 > mactra.nord-west.net.submission: Flags [P.], cksum 0x884d (correct), seq 837:943, ack 4032, win 232, options [nop,nop,TS val 5843012 ecr 118217597], length 106
14:04:36.305854 IP6 (hlim 64, next-header TCP (6) payload length: 85) mactra.nord-west.net.submission > mytilus.ipv6.nord-west.net.47200: Flags [P.], cksum 0xc127 (incorrect -> 0x3114), seq 4032:4085, ack 943, win 505, options [nop,nop,TS val 118217609 ecr 5843012], length 53
14:04:36.358164 IP6 (hlim 55, next-header TCP (6) payload length: 138) mytilus.ipv6.nord-west.net.47200 > mactra.nord-west.net.submission: Flags [P.], cksum 0x739e (correct), seq 943:1049, ack 4085, win 232, options [nop,nop,TS val 5843027 ecr 118217609], length 106
14:04:36.359512 IP6 (hlim 64, next-header TCP (6) payload length: 85) mactra.nord-west.net.submission > mytilus.ipv6.nord-west.net.47200: Flags [P.], cksum 0xc127 (incorrect -> 0xdd1b), seq 4085:4138, ack 1049, win 505, options [nop,nop,TS val 118217623 ecr 5843027], length 53
14:04:36.424323 IP6 (hlim 55, next-header TCP (6) payload length: 106) mytilus.ipv6.nord-west.net.47200 > mactra.nord-west.net.submission: Flags [P.], cksum 0x4839 (correct), seq 1049:1123, ack 4138, win 232, options [nop,nop,TS val 5843047 ecr 118217623], length 74
14:04:36.424808 IP6 (hlim 64, next-header TCP (6) payload length: 101) mactra.nord-west.net.submission > mytilus.ipv6.nord-west.net.47200: Flags [P.], cksum 0xc137 (incorrect -> 0x1d35), seq 4138:4207, ack 1123, win 505, options [nop,nop,TS val 118217639 ecr 5843047], length 69
14:04:36.478424 IP6 (hlim 55, next-header TCP (6) payload length: 210) mytilus.ipv6.nord-west.net.47200 > mactra.nord-west.net.submission: Flags [P.], cksum 0x4ef5 (correct), seq 2523:2701, ack 4207, win 232, options [nop,nop,TS val 5843063 ecr 118217639], length 178
14:04:36.478462 IP6 (hlim 64, next-header TCP (6) payload length: 44) mactra.nord-west.net.submission > mytilus.ipv6.nord-west.net.47200: Flags [.], cksum 0xc0fe (incorrect -> 0xfcc1), ack 1123, win 505, options [nop,nop,TS val 118217652 ecr 5843047,nop,nop,sack 1 {2523:2701}], length 0
14:04:36.479612 IP6 (hlim 55, next-header TCP (6) payload length: 106) mytilus.ipv6.nord-west.net.47200 > mactra.nord-west.net.submission: Flags [P.], cksum 0xecf4 (correct), seq 2701:2775, ack 4207, win 232, options [nop,nop,TS val 5843063 ecr 118217639], length 74
14:04:36.479627 IP6 (hlim 64, next-header TCP (6) payload length: 44) mactra.nord-west.net.submission > mytilus.ipv6.nord-west.net.47200: Flags [.], cksum 0xc0fe (incorrect -> 0xfc76), ack 1123, win 505, options [nop,nop,TS val 118217653 ecr 5843047,nop,nop,sack 1 {2523:2775}], length 0


In contrast, if I try to download a file from the server via IPv6, it works fine, and the routing to/from the server shows no issues.

Edit: Maybe a MTU issue? (mactra is the KVM-server, macoma the FritzBox running the tunnel over a PPPoE-ADSL2+-connection)

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bjo@mytilus ~ % ping6 -s 1500 mactra
PING mactra(mactra.nord-west.net) 1500 data bytes
From macoma.ipv6.nord-west.net icmp_seq=1 Packet too big: mtu=1480
From macoma.ipv6.nord-west.net icmp_seq=3 Packet too big: mtu=1280
1508 bytes from mactra.nord-west.net: icmp_seq=4 ttl=57 time=53.8 ms
1508 bytes from mactra.nord-west.net: icmp_seq=5 ttl=57 time=54.9 ms


I find it confusing that also 1280 should be too big and only the first both packets are affected.
I've changed the MTU from 1480 to 1472 now, we will see if it's fixed now.

[bjo]

I've got now another connection issue.

If I terminate my PPoE-connection to AS12312 and get an IP from 212.255.0.0/16, the tunnel works fine. If I terminate it to AS6805 and get an IP from 2.240.0.0/13, the tunnel get's stuck from time to time, connections hang etc. It's the same Fritzbox as tunnelendpoint, just the "exit-IP" is another. tserv1.fra1.he.net is reachable via IPv4 all the time.