AS overview
Test target: 2a0d:cec0::1 · static prefix probe · address space: PA · prefixes announced: 1
prefix(es): 2a0d:cec0::/29
Targets & per-vantage-point probe results (1 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 | ||
2a0d:cec0::1 | prb | ✓ | ✓ | ? | ? | - | ✓ | ✓ | refused | refused | - | ✓ | ✓ | refused | refused | - |
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) |
|---|---|---|---|
2a0d:cec0::/29 | ✓ valid | matched VRP (correct origin, length within maxLength) | AS201395 /29 maxLen 29 (ripe) |
Random-IP probe (yarrp) into the AS' prefixes
We probed 15 arbitrary IPv6 address(es) inside AS201395's announced prefix(es). No router inside the prefix responded. The deepest visible hop was 2a01:260:8039::a at hop 24 - that router does not answer ICMPv6 Echo. This is not in AS201395'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): 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 | 2a0d:cec0::1 | icmp6-echo | honored | 2026-05-30T10:35:47Z |
| karsolink | 2a12:d8c0:105a:9001::a154 | 2a0d:cec0::1 | icmp6-echo | inconclusive | 2026-05-30T10:45:25Z |
| odin | 2607:fae0:a000::42 | 2a0d:cec0::1 | icmp6-echo | honored | 2026-05-30T10:35:20Z |
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: [Errno 111] Connection refusedtls→ 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: [Errno 111] Connection refusedtls→ 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): AS50673, AS21283.
- From go6lab (open/Type-2=honored) the path enters AS50673 at hop 4; from odin (open/Type-2=honored) the same hop is in AS21283. Last common AS: no shared transit. 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 | * | - | - (no IP) | |
| 4 | 2001:7f8:46::2:1283 | AS21283 | A1 Slovenija | ? no_response |
| 5 | 2001:15c0:2304:3::1 | AS21283 | A1SI-AS - A1 Slovenija telekomunikacijsk | ? no_response |
| 6 | 2001:15c0:2304:3::42 | AS21283 | A1SI-AS - A1 Slovenija telekomunikacijsk | ? 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.
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 | 1.1ms | 0% | AS203993 | STEFFANN-DC-AS - S.J.M. Steffann, NL |
| 2 | * | - | - | - | |
| 3 | 2a00:1ca8:1::194 | 2.5ms | 10% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 4 | 2a03:3f40::10:33 | 6.8ms | 0% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 5 | t-2.interxionfra11.nlsix.net 2001:7f8:13::a503:4779:1 | 34.3ms | 0% | - | NA |
| 6 | 2a01-260-1-1--25.core6.t-2.net 2a01:260:1:1::25 | 41.0ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 7 | 2a01-260-1-1--71.core6.t-2.net 2a01:260:1:1::71 | 39.0ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 8 | 2a01-260-8039--a.link6.t-2.net 2a01:260:8039::a | 43.3ms | 0% | AS34779 | T-2-AS - T-2, 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] 0.039ms pmtu 1500
1: 2a00:8642:42::3 1.815ms
1: 2a00:8642:42::3 1.636ms
2: no reply
3: 2a00:1ca8:1::194 2.507ms
4: 2a03:3f40::10:33 5.799ms
5: t-2.interxionfra11.nlsix.net 34.384ms asymm 6
6: 2a01-260-1-1--25.core6.t-2.net 42.290ms asymm 7
7: 2a01-260-1-1--71.core6.t-2.net 39.693ms asymm 8
8: 2a01-260-8039--a.link6.t-2.net 44.508ms reached
Resume: pmtu 1500 hops 8 back 10 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 | * | - | - | - | |
| 2 | * | - | - | - | |
| 3 | * | - | 50% | - | |
| 4 | * | - | - | - | |
| 5 | 100ge0-0-0-20.core1.vie1.he.net 2001:470:0:414::1 | 21.5ms | 0% | AS6939 | HURRICANE - Hurricane Electric LLC, US |
| 6 | 2001:7f8:30:0:2:1:3:4779 | 20.0ms | 0% | - | NA |
| 7 | 2a01:260:1:1::109 | 26.1ms | 0% | AS34779 | T-2-AS - T-2, d.o.o., SI |
| 8 | 2a01-260-8039--a.link6.t-2.net 2a01:260:8039::a | 44.5ms | 0% | AS34779 | T-2-AS - T-2, 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] 0.069ms pmtu 1500
1: no reply
2: no reply
3: 2a12:d8c0:101f:6::1 10.226ms
4: no reply
5: 100ge0-0-0-20.core1.vie1.he.net 21.550ms
6: 2001:7f8:30:0:2:1:3:4779 20.314ms
7: 2a01:260:1:1::109 20.835ms
8: 2a01-260-8039--a.link6.t-2.net 44.737ms reached
Resume: pmtu 1500 hops 8 back 12 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 | 1.0ms | 0%* | AS8038 | 6CONNECT - 6connect, Inc., US |
| 2 | * | - | - | - | |
| 3 | * | - | - | - | |
| 4 | six.a1.si @SIX 2001:7f8:46::2:1283 | 1.9ms | 0% | AS21283 | A1 Slovenija |
| 5 | 2001:15c0:2304:3::1 | 3.9ms | 0% | AS21283 | A1SI-AS - A1 Slovenija telekomunikacijske storitve,d.d., SI |
| 6 | 2001:15c0:2304:3::42 | 5.0ms | 0% | AS21283 | A1SI-AS - A1 Slovenija telekomunikacijske storitve,d.d., SI |
tracepath -6
1?: [LOCALHOST] 0.031ms pmtu 1500
1: fw1-lju.6connect.com 0.437ms
1: fw1-lju.6connect.com 0.313ms
2: no reply
3: no reply
4: six.t-2.si 1.253ms
5: 2001:15c0:2304:3::1 3.620ms asymm 6
6: 2001:15c0:2304:3::42 3.575ms reached
Resume: pmtu 1500 hops 6 back 7