AS overview
Test target: 2a0c:b641:4c0:: · via IPv6 Hitlist (responsive) · address space: PA · prefixes announced: 1
prefix(es): 2a0c:b641:4c0::/44
Targets & per-vantage-point probe results (2 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 | ||
2a0c:b641:4c0:1::3 | rtr | ✓ | ✗ | ? | ? | ✓ | ✓ | ✗ | ? | ? | ✓ | ✓ | ✗ | ? | ? | ✓ |
2a0c:b641:4c0:: | hit | ✓ | ✓ | ? | ? | - | ✓ | ✓ | ? | ? | - | ✓ | ✓ | ? | ? | - |
RPKI & ASPA
1 of 1 prefix(es) covered by a valid ROA.
| Prefix | RPKI state | Reason | Covering VRP(s) |
|---|---|---|---|
2a0c:b641:4c0::/44 | ✓ valid | matched VRP (correct origin, length within maxLength) | AS205211 /44 maxLen 128 (ripe) |
Random-IP probe (yarrp) into the AS' prefixes
At least one router inside AS205211's announced prefix replied during the random-target probe. Hop(s): 2a0c:b641:4c0::. These are candidate targets for direct testing.
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): Type 2 honored. Forged PTB accepted; next response shrunk. (ICMPv6 Echo + forged PTB)
- ITA host (Karsolink): inconclusive: no Echo Reply after PTB (probe 1500B). (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 | 2a0c:b641:4c0:: | icmp6-echo | honored | 2026-05-30T10:35:47Z |
| karsolink | 2a12:d8c0:105a:9001::a154 | 2a0c:b641:4c0:: | icmp6-echo | inconclusive | 2026-05-30T10:45:25Z |
| odin | 2607:fae0:a000::42 | 2a0c:b641:4c0:: | icmp6-echo | honored | 2026-05-30T10:35:21Z |
Attempt log (go6lab):
icmp6-echo→ honored (size_before=1460, size_after=None)dns-tcp→ no_tcp: connect failed: timed outtls→ no_tcp: TLS connect failedhttp→ no_tcp: tcp/80 not open
Attempt log (karsolink):
icmp6-echo→ inconclusive (size_before=1460, size_after=None): no Echo Reply after PTB (probe 1500B)dns-tcp→ no_tcp: connect failed: timed outtls→ 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→ no_tcp: connect failed: timed outtls→ 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→ verdicthonored - karsolink: probe
icmp6-echo→ verdictinconclusive - odin: probe
icmp6-echo→ verdicthonored
Full per-method matrix (all four methods run at each vantage):
| vantage | icmp6-echo | dns-tcp | tls | http |
|---|---|---|---|---|
| go6lab | honored | no_tcp | no_tcp | no_tcp |
| karsolink | inconclusive | no_tcp | no_tcp | no_tcp |
| odin | honored | no_tcp | 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): AS24961, AS34872, AS50673.
- From go6lab (open/Type-2=honored) the path enters AS34872 at hop 9; from karsolink (open/Type-2=inconclusive) the same hop is in AS24961. Last common AS: AS34872. The disagreement is most likely rooted in one of those two transit ASes.
- From go6lab (open/Type-2=honored) the path enters AS50673 at hop 3; from odin (open/Type-2=honored) the same hop is in AS5603. Last common AS: AS34872. The disagreement is most likely rooted in one of those two transit ASes.
- From karsolink (open/Type-2=inconclusive) the path enters AS24961 at hop 9; from odin (open/Type-2=honored) the same hop is in AS5405. Last common AS: AS34872. 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.
First break at hop 3: AS5603 (SIOL-NET - Telekom Slovenije, d.d., SI) -- this is the most likely site of the offending PTB filter. Hop IP: 2a00:ee1:800:9::1.
| # | hop IP | AS | Holder | PTB acceptance |
|---|---|---|---|---|
| 1 | 2607:fae0:a000::2 | AS8038 | 6CONNECT - 6connect, Inc., US | - skipped (CoPP) |
| 2 | * | - | - (no IP) | |
| 3 | 2a00:ee1:800:9::1 | AS5603 | SIOL-NET - Telekom Slovenije, d.d., SI | ✗ not_honored |
| 4 | 2a00:ee0:1:15::2 | AS5603 | SIOL-NET - Telekom Slovenije, d.d., SI | ✗ not_honored |
| 5 | 2a11:4142:2002 | - | - (invalid IP) | |
| 6 | 2a11:4140::1e | AS5405 | INTERDOTLINK - Inter.link GmbH, DE | ✓ honored |
| 7 | 2a11:4140::20 | AS5405 | INTERDOTLINK - Inter.link GmbH, DE | ✓ honored |
| 8 | 2a11:4140::1f | AS5405 | INTERDOTLINK - Inter.link GmbH, DE | ✓ honored |
| 9 | 2a11:4140::1c | AS5405 | INTERDOTLINK - Inter.link GmbH, DE | ✓ honored |
| 10 | 2001:7f8:44::151d:0:1 | - | NA | ? no_response |
| 11 | 2001:7f8:44::8838:0:1 | - | NA | ? no_response |
| 12 | 2a0c:b640:ffff:100:120:7:128:134 | AS34872 | Servperso_Systems - Sarah Rossius tradin | ? no_response |
| 13 | * | - | - (no IP) | |
| 14 | * | - | - (no IP) | |
| 15 | * | - | - (no IP) | |
| 16 | * | - | - (no IP) | |
| 17 | * | - | - (no IP) | |
| 18 | * | - | - (no IP) | |
| 19 | * | - | - (no IP) | |
| 20 | * | - | - (no IP) | |
| 21 | * | - | - (no IP) | |
| 22 | * | - | - (no IP) | |
| 23 | * | - | - (no IP) | |
| 24 | * | - | - (no IP) |
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.
From NL host (go6lab) openRFC 4890 ✓
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 | 1.5ms | 0% | AS203993 | STEFFANN-DC-AS - S.J.M. Steffann, NL |
| 2 | * | - | 0%* | - | |
| 3 | 2a00:1ca8:1::194 | 2.7ms | 0% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 4 | 2a03:3f40::10:33 | 3.5ms | 0% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 5 | po15-h437c.core1-ams-ni.bb.as24961.net 2001:7f8:1::a502:4961:1 | 4.0ms | 0% | - | NA |
| 6 | lag15.core2-dus3.bb.wiit.network 2001:4ba0:ffe9:10::1 | 7.3ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 7 | lag2-h3679.edge3-dus3.bb.wiit.network 2001:4ba0:ffe9:7a::2 | 8.7ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 8 | 2001:4ba0:dead:b051::3 | 7.4ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 9 | 2a0c-b640-ffff-100-120-7-128-134.edge.isp.servpersosystems.net 2a0c:b640:ffff:100:120:7:128:134 | 7.7ms | 0% | AS34872 | Servperso_Systems - Sarah Rossius trading as Servperso Systems, BE |
| 10 | * | - | 0% | - | |
| 11 | * | - | - | - | |
| 12 | * | - | - | - | |
| 13 | * | - | - | - | |
| 14 | * | - | - | - | |
| 15 | * | - | - | - | |
| 16 | * | - | - | - | |
| 17 | * | - | - | - | |
| 18 | * | - | - | - | |
| 19 | * | - | - | - | |
| 20 | * | - | - | - | |
| 21 | * | - | - | - | |
| 22 | * | - | - | - | |
| 23 | * | - | - | - | |
| 24 | * | - | - | - |
tracepath -6
1?: [LOCALHOST] 0.029ms pmtu 1500
1: 2a00:8642:42::3 1.486ms
1: 2a00:8642:42::3 1.427ms
2: gw.friends.steffann.nl 2.405ms
3: 2a00:1ca8:1::194 2.755ms
4: 2a03:3f40::10:33 4.714ms
5: po15-h437c.core1-ams-ni.bb.as24961.net 4.900ms asymm 4
6: lag15.core2-dus3.bb.wiit.network 7.744ms asymm 5
7: lag2-h3679.edge3-dus3.bb.wiit.network 10.872ms asymm 6
8: 2001:4ba0:dead:b051::3 8.032ms asymm 7
9: 2a0c-b640-ffff-100-120-7-128-134.edge.isp.servpersosystems.net 8.641ms asymm 8
10: no reply
11: no reply
12: no reply
13: no reply
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16: no reply
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19: no reply
20: no reply
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23: no reply
24: no reply
Too many hops: pmtu 1500
Resume: pmtu 1500 From ITA host (Karsolink) open
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 | 0%* | AS204471 | KARSOLINK - 2S Computers SRL, IT |
| 3 | 2a12:d8c0:101f:6::1 | 10.0ms | 10% | AS204471 | KARSOLINK - 2S Computers SRL, IT |
| 4 | myloc.minap.it 2001:7f8:c5::a502:4961:1 | 10.2ms | 0% | - | NA |
| 5 | 2001:4ba0:ffe9:c6 | 13.9ms | 0% | - | |
| 6 | lag0-vl1017.core1-fra-eq5.bb.wiit.network 2001:4ba0:ffe9:b7::1 | 18.9ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 7 | lag0-vl7.core1-fra-ix.bb.wiit.network 2001:4ba0:ffe9:6d::2 | 19.2ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 8 | lag26.core3-dus1.bb.wiit.network 2001:4ba0:ffe9:8a::1 | 22.8ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 9 | lag2.core2-dus3.bb.wiit.network 2001:4ba0:ffe9::1 | 22.5ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 10 | lag2-h3679.edge3-dus3.bb.wiit.network 2001:4ba0:ffe9:7a::2 | 25.0ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 11 | 2001:4ba0:dead:b051::3 | 23.0ms | 0% | AS24961 | MYLOC-AS - WIIT AG, DE |
| 12 | 2a0c-b640-ffff-100-120-7-128-134.edge.isp.servpersosystems.net 2a0c:b640:ffff:100:120:7:128:134 | 22.8ms | 0% | AS34872 | Servperso_Systems - Sarah Rossius trading as Servperso Systems, BE |
| 13 | * | - | 0% | - | |
| 14 | * | - | - | - | |
| 15 | * | - | - | - | |
| 16 | * | - | - | - | |
| 17 | * | - | - | - | |
| 18 | * | - | - | - | |
| 19 | * | - | - | - | |
| 20 | * | - | - | - | |
| 21 | * | - | - | - | |
| 22 | * | - | - | - | |
| 23 | * | - | - | - | |
| 24 | * | - | - | - |
Rate-limited ICMPv6: hop 3 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).
tracepath -6
1?: [LOCALHOST] 0.033ms pmtu 1500
1: karsolink-01.net.karsolink.com 0.638ms
1: karsolink-01.net.karsolink.com 0.852ms
2: no reply
3: 2a12:d8c0:101f:6::1 10.568ms
4: myloc.minap.it 10.714ms
5: lag0-vl1002.core1-lpg-green-lu2.bb.wiit.network 15.064ms
6: lag0-vl1017.core1-fra-eq5.bb.wiit.network 19.702ms
7: lag0-vl7.core1-fra-ix.bb.wiit.network 19.642ms
8: lag26.core3-dus1.bb.wiit.network 23.499ms
9: lag2.core2-dus3.bb.wiit.network 23.346ms
10: lag2-h3679.edge3-dus3.bb.wiit.network 25.949ms
11: 2001:4ba0:dead:b051::3 23.708ms asymm 9
12: 2a0c-b640-ffff-100-120-7-128-134.edge.isp.servpersosystems.net 23.476ms
13: no reply
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15: no reply
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21: no reply
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24: no reply
Too many hops: pmtu 1500
Resume: pmtu 1500 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 | 0.4ms | 0%* | AS8038 | 6CONNECT - 6connect, Inc., US |
| 2 | * | - | - | - | |
| 3 | 2a00:ee1:800:9::1 | 1.8ms | 0% | AS5603 | SIOL-NET - Telekom Slovenije, d.d., SI |
| 4 | 2a00:ee0:1:15::2 | 1.0ms | 0% | AS5603 | SIOL-NET - Telekom Slovenije, d.d., SI |
| 5 | 2a11:4142:2002 | 1.0ms | 0% | - | |
| 6 | r2-vie1-at.as5405.net 2a11:4140::1e | 13.0ms | 0% | AS5405 | INTERDOTLINK - Inter.link GmbH, DE |
| 7 | r2-vie2-at.as5405.net 2a11:4140::20 | 13.1ms | 0% | AS5405 | INTERDOTLINK - Inter.link GmbH, DE |
| 8 | r1-vie2-at.as5405.net 2a11:4140::1f | 12.9ms | 0% | AS5405 | INTERDOTLINK - Inter.link GmbH, DE |
| 9 | r1-muc1-de.as5405.net 2a11:4140::1c | 12.7ms | 0% | AS5405 | INTERDOTLINK - Inter.link GmbH, DE |
| 10 | 2001:7f8:44::151d:0:1 | 12.8ms | 0% | - | NA |
| 11 | muc.as34872-decix.servperso.net 2001:7f8:44::8838:0:1 | 21.3ms | 0% | - | NA |
| 12 | 2a0c-b640-ffff-100-120-7-128-134.edge.isp.servpersosystems.net 2a0c:b640:ffff:100:120:7:128:134 | 21.5ms | 0% | AS34872 | Servperso_Systems - Sarah Rossius trading as Servperso Systems, BE |
| 13 | * | - | 0% | - | |
| 14 | * | - | - | - | |
| 15 | * | - | - | - | |
| 16 | * | - | - | - | |
| 17 | * | - | - | - | |
| 18 | * | - | - | - | |
| 19 | * | - | - | - | |
| 20 | * | - | - | - | |
| 21 | * | - | - | - | |
| 22 | * | - | - | - | |
| 23 | * | - | - | - | |
| 24 | * | - | - | - |
tracepath -6
1?: [LOCALHOST] 0.022ms pmtu 1500
1: fw1-lju.6connect.com 0.421ms
1: fw1-lju.6connect.com 0.398ms
2: no reply
3: 2a00:ee1:800:9::1 2.147ms
4: 2a00:ee0:1:15::2 0.985ms asymm 3
5: 2a11:4142:2002:: 0.942ms asymm 6
6: r2-vie1-at.as5405.net 12.680ms asymm 14
7: r2-vie2-at.as5405.net 12.639ms asymm 14
8: r1-vie2-at.as5405.net 12.675ms asymm 13
9: r1-muc1-de.as5405.net 12.894ms asymm 12
10: 2001:7f8:44::151d:0:1 12.631ms
11: muc.as34872-decix.servperso.net 21.432ms asymm 8
12: 2a0c-b640-ffff-100-120-7-128-134.edge.isp.servpersosystems.net 21.650ms asymm 10
13: no reply
14: no reply
15: no reply
16: no reply
17: no reply
18: no reply
19: no reply
20: no reply
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23: no reply
24: no reply
Too many hops: pmtu 1500
Resume: pmtu 1500