AS overview
Test target: 2a05:33c0:0:1::11 · via IPv6 Hitlist (responsive) · address space: PA · prefixes announced: 1
prefix(es): 2a05:33c0::/48
Targets & per-vantage-point probe results (5 target(s) across 3 vantage point(s))
Source codes (hover any badge for full description): CUR=curated · NS/SOA/MX=DNS records · SPF=SPF TXT · DRV=holder-derived (www, ns1, mail, gw, …) · ATL=RIPE Atlas · PDB=PeeringDB · WHOIS=RIPE whois · RDAP=RIPE RDAP · HIT=IPv6 Hitlist · RTR=in-prefix path hop (router) · PRB=static prefix probe · SYN=synthetic prefix::1 fallback
| Target IP / hostname | Source | NL host (go6lab) | ITA host (Karsolink) | SLO host (6connect) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ping | 1500B | :80 | :443 | reached | ping | 1500B | :80 | :443 | reached | ping | 1500B | :80 | :443 | reached | ||
2a05:33c0:0:1::11 | hit | ✓ | ✓ | ? | ? | ✓ | ✓ | ✓ | refused | refused | ✓ | ✓ | ✓ | refused | refused | ✓ |
2a05:33c0:0:1::62 | hit | ✓ | ✓ | open | open | ✓ | ✓ | ✓ | open | open | ✓ | ✓ | ✓ | open | open | ✓ |
2a05:33c0:0:1::77 | hit | ✓ | ✓ | open | open | ✓ | ✓ | ✓ | open | open | ✓ | ✓ | ✓ | open | open | ✓ |
2a05:33c0::1 | prb | ✓ | ✓ | ? | ? | - | ✓ | ✓ | ? | ? | - | ✓ | ✓ | ? | ? | - |
2a05:33c0::3 | hit | ✓ | ✓ | ? | ? | - | ✓ | ✓ | ? | ? | - | ✓ | ✓ | ? | ? | - |
SIX peering
Not an SIX member, but our traceroute path crosses the SIX LAN from SLO host (6connect) - reached via an SIX-resident transit operator.
RPKI & ASPA
1 of 1 prefix(es) covered by a valid ROA.
| Prefix | RPKI state | Reason | Covering VRP(s) |
|---|---|---|---|
2a05:33c0::/48 | ✓ valid | matched VRP (correct origin, length within maxLength) | AS201522 /48 maxLen 48 (ripe) |
Random-IP probe (yarrp) into the AS' prefixes
We probed 15 arbitrary IPv6 address(es) inside AS201522's announced prefix(es). No router inside the prefix responded. The deepest visible hop was 2a01:260:4057::12 at hop 14 - that router answers ICMPv6 Echo. This is not in AS201522's announced prefix; operationally it's the AS-edge / peering interface (often on a SIX peering address or an upstream's /127 link). The traceroute boundary is the AS edge: ICMPv6 Time-Exceeded responses from anything inside this AS are filtered.
ICMPv6 Type 2 (Packet Too Big) acceptance - active test
Vantage points disagree about Type 2 acceptance - transit ASes on one path may be filtering Type 2 even though the destination's stack accepts it on another path:
- NL host (go6lab): inconclusive: no Echo Reply after PTB (probe 1500B). (ICMPv6 Echo + forged PTB)
- ITA host (Karsolink): Type 2 honored. Forged PTB accepted; next response shrunk. (ICMPv6 Echo + forged PTB)
- SLO host (6connect): Type 2 honored. Forged PTB accepted; next response shrunk. (ICMPv6 Echo + forged PTB)
Why they disagree - measurement artifact: One vantage's probe didn't generate enough data to detect segment shrinkage (natural reply too small, or no second response). The other vantage's verdict is the meaningful one.
Failure detail — what to grep in your logs
| vantage | our source | your target | method | result | tested (UTC) |
|---|---|---|---|---|---|
| go6lab | 2a00:8642:42::75 | 2a05:33c0:0:1::11 | icmp6-echo | inconclusive | 2026-05-30T10:35:17Z |
| karsolink | 2a12:d8c0:105a:9001::a154 | 2a05:33c0:0:1::11 | icmp6-echo | honored | 2026-05-30T10:44:49Z |
| odin | 2607:fae0:a000::42 | 2a05:33c0:0:1::11 | icmp6-echo | honored | 2026-05-30T10:34:55Z |
Attempt log (go6lab):
icmp6-echo→ inconclusive (size_before=1460, size_after=None): no Echo Reply after PTB (probe 1500B)dns-tcp→ inconclusive (size_before=88, size_after=None): max DNS-over-TCP segment 88B; not big enough to test PMTU shrinktls→ no_tcp: TLS connect failedhttp→ no_tcp: tcp/80 not open
Attempt log (karsolink):
icmp6-echo→ honored (size_before=1360, size_after=None)dns-tcp→ inconclusive (size_before=156, size_after=None): max DNS-over-TCP segment 156B; not big enough to test PMTU shrinktls→ no_tcp: TLS connect failedhttp→ no_tcp: tcp/80 not open
Attempt log (odin):
icmp6-echo→ honored (size_before=1360, size_after=None): natural Echo Reply at 1400B was already split into IPv6 fragments without our PTB intervention -- the destination's stack has a cached path MTU below 1400B from a previously-honored ICMPv6 Type 2, which is itself evidence that this destination honors PTB on this path.dns-tcp→ inconclusive (size_before=156, size_after=None): max DNS-over-TCP segment 156B; not big enough to test PMTU shrinktls→ no_tcp: TLS connect failedhttp→ no_tcp: tcp/80 not open
To match the corresponding ICMPv6 packet on your side (host firewall, AS edge, or transit tap), look for our PTBs around the timestamps above:
sudo tcpdump -i any -n -e 'icmp6 and ip6[40] = 2 and (src host 2607:fae0:a000::42 or src host 2a00:8642:42::75 or src host 2a12:d8c0:105a:9001::a154)'
If you see our PTBs arriving but the destination's TCP/Echo flow does not shrink, the drop is in the destination kernel (cause 3 below). If you don't see them at all, drop is upstream of you (cause 2). If you only see them from one of our two source IPs, the drop is path-asymmetric — one transit on the asymmetric route is filtering, the other is not.
Where the path divergence is
Per-vantage probe + verdict (headline):
- go6lab: probe
icmp6-echo→ verdictinconclusive - karsolink: probe
icmp6-echo→ verdicthonored - odin: probe
icmp6-echo→ verdicthonored
Full per-method matrix (all four methods run at each vantage):
| vantage | icmp6-echo | dns-tcp | tls | http |
|---|---|---|---|---|
| go6lab | inconclusive | inconclusive | no_tcp | no_tcp |
| karsolink | honored | inconclusive | no_tcp | no_tcp |
| odin | honored | inconclusive | no_tcp | no_tcp |
✓ All vantages agree on method(s): icmp6-echo — the headline-method spread above is dispatcher noise, not a real Type 2 disagreement.
These vantage-level disagreements are rooted somewhere in the forward paths. Joining each per-vantage traceroute against the IP→AS lookup from our global yarrp mesh, the first hop where the paths land in different ASes is the most likely site of the offending filter / unreachable AS / Type 2 drop.
Suspect transit ASes (ranked by how often they appear at the divergence point on the path of the worse-classifying vantage): AS201522, AS34779, AS50673.
- From go6lab (open/Type-2=inconclusive) the path enters AS201522 at hop 8; from karsolink (open/Type-2=honored) the same hop is in AS34779. Last common AS: AS201522. The disagreement is most likely rooted in one of those two transit ASes.
- From go6lab (open/Type-2=inconclusive) the path enters AS50673 at hop 3; from odin (open/Type-2=honored) the same hop is in AS56635. Last common AS: AS201522. The disagreement is most likely rooted in one of those two transit ASes.
- From karsolink (open/Type-2=honored) the path enters AS34779 at hop 7; from odin (open/Type-2=honored) the same hop is in AS201522. Last common AS: AS201522. The disagreement is most likely rooted in one of those two transit ASes.
Diagnosis is path-level, not packet-level: it tells you which transit AS is the prime suspect, not exactly which firewall rule is to blame. Use the tracepath6 output below (when available) for per-hop PMTU evidence on the same path.
✨ Diagnostic interpretation
Per-hop PTB acceptance walk
From the local vantage, we walk the forward path hop-by-hop, sending each hop a 1500-byte ICMPv6 Echo, then a forged PTB (MTU=1280) sourced from us, then another 1500-byte Echo. If the second reply arrives fragmented or smaller, that hop honoured the PTB. If unchanged, it didn't. The first ✗ in an otherwise-✓ path is the most likely filter location. Cross-country aggregation: see the global PTB filter atlas for transit ASes ranked by filter rate across all measurements.
| # | hop IP | AS | Holder | PTB acceptance |
|---|---|---|---|---|
| 1 | 2607:fae0:a000::2 | AS8038 | 6CONNECT - 6connect, Inc., US | - skipped (CoPP) |
| 2 | * | - | - (no IP) | |
| 3 | 2a03:a100:0:201:1::1 | AS56635 | XENYA - XENYA inzeniring, proizvodnja in | ✓ honored |
| 4 | 2001:7f8:46::3:4779 | AS34779 | T-2 | ✓ honored |
| 5 | 2a01:260:1:1::93 | AS34779 | T-2-AS - T-2, d.o.o., SI | ✓ honored |
| 6 | 2a01:260:4057::12 | AS34779 | T-2-AS - T-2, d.o.o., SI | ? no_response |
| 7 | 2a05:33c0::3 | AS201522 | UB330-net - UB330.net d.o.o., SI | ? no_response |
| 8 | 2a05:33c0:0:1::11 | AS201522 | UB330-net - UB330.net d.o.o., SI | ? no_response |
Tests host-mode PTB acceptance (PTBs aimed at the hop itself). A router that honours PTBs to itself can still be filtering PTBs transiting through it; this is one indicator, not proof of full PTB transparency. Hops in CoPP-rate-limit ranges are skipped to avoid false signals.
tracepath6 per-hop PMTU drilldown
For each target where Type 2 verdicts disagreed across vantages, tracepath -6 ran from every vantage to capture per-hop PMTU evolution along that vantage's actual forward path. A pmtu change entry on a hop means that hop's router generated a PTB and we observed the shrink; absence of any change combined with a not_honored verdict suggests a router somewhere downstream is silently dropping >MTU packets (an RFC 4890 violation) rather than sending a PTB.
Target 2a05:33c0:0:1::62
go6lab — verdict not_honored
verdict = not_honored; final pmtu = 1500
| # | hop IP | pmtu change |
|---|---|---|
| 1 | <span class='muted'>no reply</span> | |
| 2 | 2a00:8642:1000:f000::1 | |
| 3 | 2a00:1ca8:1::194 | |
| 4 | 2a03:3f40::10:33 | |
| 5 | 2001:7f8:13::a503:4779:1 | |
| 6 | 2a01:260:1:1::95 | |
| 7 | 2a01:260:4057::12 | |
| 8 | 2a05:33c0::3 | |
| 9 | 2a05:33c0:0:1::62 |
karsolink — verdict honored
verdict = honored; final pmtu = 1500
| # | hop IP | pmtu change |
|---|---|---|
| 1 | <span class='muted'>no reply</span> | |
| 2 | 2a12:d8c0:109f:121::a1 | |
| 3 | 2a12:d8c0:101f:6::1 | |
| 4 | <span class='muted'>no reply</span> | |
| 5 | 2001:470:0:414::1 | |
| 6 | 2001:7f8:30:0:2:1:3:4779 | |
| 7 | 2a01:260:1:1::d | |
| 8 | 2a01:260:1:1::93 | |
| 9 | 2a01:260:4057::12 | |
| 10 | 2a05:33c0::3 | |
| 11 | 2a05:33c0:0:1::62 |
odin — verdict honored
verdict = honored; final pmtu = 1500
| # | hop IP | pmtu change |
|---|---|---|
| 1 | <span class='muted'>no reply</span> | |
| 2 | 2607:fae0:a000:2::2 | |
| 3 | 2a03:a100:0:201:1::1 | |
| 4 | 2001:7f8:46::3:4779 | |
| 5 | 2a01:260:1:1::93 | |
| 6 | 2a01:260:4057::12 | |
| 7 | 2a05:33c0::3 | |
| 8 | 2a05:33c0:0:1::62 |
From NL host (go6lab) open
filter likely at: (none) · min PMTU on path: 1500
Path (traceroute + mtr + PTR)
| # | IP / PTR | RTT | mtr loss | AS | AS holder |
|---|---|---|---|---|---|
| 1 | 2a00:8642:42::3 | 1.7ms | 0% | AS203993 | STEFFANN-DC-AS - S.J.M. Steffann, NL |
| 2 | gw.friends.steffann.nl 2a00:8642:1000:f000::1 | 2.1ms | 0%* | AS203993 | STEFFANN-DC-AS - S.J.M. Steffann, NL |
| 3 | 2a00:1ca8:1::194 | 2.1ms | 10% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 4 | 2a03:3f40::10:33 | 4.9ms | 0% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 5 | t-2.interxionfra11.nlsix.net 2001:7f8:13::a503:4779:1 | 34.5ms | 0% | - | NA |
| 6 | 2a01-260-1-1--95.core6.t-2.net 2a01:260:1:1::95 | 36.8ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 7 | 2a01-260-4057--12.link6.t-2.net 2a01:260:4057::12 | 36.8ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 8 | 2a05:33c0::3 | 39.1ms | 0% | AS201522 | UB330-net - UB330.net d.o.o., SI |
| 9 | delphi.powercom.si 2a05:33c0:0:1::11 | 39.6ms | 10% | AS201522 | UB330-net - UB330.net d.o.o., SI |
Rate-limited ICMPv6: hop 3, hop 9 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).
tracepath -6
1?: [LOCALHOST] 0.034ms pmtu 1500
1: 2a00:8642:42::3 2.173ms
1: 2a00:8642:42::3 1.590ms
2: no reply
3: 2a00:1ca8:1::194 3.188ms
4: 2a03:3f40::10:33 6.021ms
5: t-2.interxionfra11.nlsix.net 34.553ms asymm 6
6: 2a01-260-1-1--95.core6.t-2.net 39.727ms asymm 7
7: 2a01-260-4057--12.link6.t-2.net 38.656ms asymm 8
8: 2a05:33c0::3 36.565ms asymm 9
9: delphi.powercom.si 38.126ms reached
Resume: pmtu 1500 hops 9 back 11 From ITA host (Karsolink) openRFC 4890 ✓
filter likely at: (none) · min PMTU on path: 1500
Path (traceroute + mtr + PTR)
| # | IP / PTR | RTT | mtr loss | AS | AS holder |
|---|---|---|---|---|---|
| 1 | * | - | 0%* | - | |
| 2 | 2a12:d8c0:109f:121::a1 | 0.4ms | - | AS204471 | KARSOLINK - 2S Computers SRL, IT |
| 3 | 2a12:d8c0:101f:6::1 | 10.0ms | - | AS204471 | KARSOLINK - 2S Computers SRL, IT |
| 4 | * | - | - | - | |
| 5 | 100ge0-0-0-20.core1.vie1.he.net 2001:470:0:414::1 | 21.7ms | 0% | AS6939 | HURRICANE - Hurricane Electric LLC, US |
| 6 | 2001:7f8:30:0:2:1:3:4779 | 20.2ms | 0% | - | NA |
| 7 | 2a01-260-1-1--d.core6.t-2.net 2a01:260:1:1::d | 44.4ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 8 | 2a01-260-1-1--93.core6.t-2.net 2a01:260:1:1::93 | 43.7ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 9 | 2a01-260-4057--12.link6.t-2.net 2a01:260:4057::12 | 45.9ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 10 | 2a05:33c0::3 | 46.8ms | 0% | AS201522 | UB330-net - UB330.net d.o.o., SI |
| 11 | delphi.powercom.si 2a05:33c0:0:1::11 | 45.8ms | 0% | AS201522 | UB330-net - UB330.net d.o.o., SI |
tracepath -6
1?: [LOCALHOST] 0.032ms pmtu 1500
1: karsolink-01.net.karsolink.com 1.232ms
1: karsolink-01.net.karsolink.com 0.889ms
2: 2a12:d8c0:109f:121::a1 0.936ms
3: 2a12:d8c0:101f:6::1 10.682ms
4: no reply
5: 100ge0-0-0-20.core1.vie1.he.net 22.435ms
6: 2001:7f8:30:0:2:1:3:4779 20.412ms
7: 2a01-260-1-1--d.core6.t-2.net 44.885ms asymm 10
8: 2a01-260-1-1--93.core6.t-2.net 43.484ms asymm 10
9: 2a01-260-4057--12.link6.t-2.net 47.022ms asymm 11
10: 2a05:33c0::3 47.296ms asymm 12
11: delphi.powercom.si 45.260ms reached
Resume: pmtu 1500 hops 11 back 13 From SLO host (6connect) openRFC 4890 ✓
filter likely at: (none) · min PMTU on path: 1500
Path (traceroute + mtr + PTR)
| # | IP / PTR | RTT | mtr loss | AS | AS holder |
|---|---|---|---|---|---|
| 1 | fw1-lju.6connect.com 2607:fae0:a000::2 | 0.3ms | 0%* | AS8038 | 6CONNECT - 6connect, Inc., US |
| 2 | * | - | - | - | |
| 3 | 2a03:a100:0:201:1::1 | 0.5ms | 50% | AS56635 | XENYA - XENYA inzeniring, proizvodnja in trgovina, d.o.o. Ljubljana, SI |
| 4 | six.t-2.si @SIX 2001:7f8:46::3:4779 | 1.1ms | 0% | AS34779 | T-2 |
| 5 | 2a01-260-1-1--93.core6.t-2.net 2a01:260:1:1::93 | 1.6ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 6 | 2a01-260-4057--12.link6.t-2.net 2a01:260:4057::12 | 2.4ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 7 | 2a05:33c0::3 | 3.6ms | 0% | AS201522 | UB330-net - UB330.net d.o.o., SI |
| 8 | delphi.powercom.si 2a05:33c0:0:1::11 | 3.6ms | 0% | AS201522 | UB330-net - UB330.net d.o.o., SI |
Rate-limited ICMPv6: hop 3 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).
tracepath -6
1?: [LOCALHOST] 0.045ms pmtu 1500
1: fw1-lju.6connect.com 0.660ms
1: fw1-lju.6connect.com 0.739ms
2: no reply
3: 2a03:a100:0:201:1::1 0.827ms
4: six.t-2.si 1.123ms
5: 2a01-260-1-1--93.core6.t-2.net 3.008ms
6: 2a01-260-4057--12.link6.t-2.net 3.402ms
7: 2a05:33c0::3 3.075ms
8: delphi.powercom.si 4.959ms reached
Resume: pmtu 1500 hops 8 back 8