AS overview
Test target: 2a00:1be0:85:69:40:: · micso.it · address space: PA · prefixes announced: 1
prefix(es): 2a00:1be0::/32
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 | ||
2a00:1be0:85:69:40::micso.it | drv | ✓ | ✓ | open | open | - | ✓ | ✓ | open | open | - | ✓ | ✓ | open | open | - |
RPKI & ASPA
1 of 1 prefix(es) covered by a valid ROA.
| Prefix | RPKI state | Reason | Covering VRP(s) |
|---|---|---|---|
2a00:1be0::/32 | ✓ valid | matched VRP (correct origin, length within maxLength) | AS21034 /32 maxLen 32 (ripe) |
ASPA: this AS has published an ASPA record listing 3 upstream provider(s) that are authorized to propagate routes from it: AS3269, AS8928, AS12874. Routes from this AS that arrive via any other upstream are considered ASPA-invalid by validators that enforce ASPA.
Random-IP probe (yarrp) into the AS' prefixes
At least one router inside AS21034's announced prefix replied during the random-target probe. Hop(s): 2a00:1be0:0:97::257. 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): Type 2 partial. Some shrinkage but not down to 1280 bytes. (TLS handshake + forged PTB)
- SLO host (6connect): Type 2 honored. Forged PTB accepted; next response shrunk. (ICMPv6 Echo + forged PTB)
Why they disagree - different probe methods: These vantages picked different probe methods, so their verdicts are not directly comparable. The active test tries methods in order (icmp6-echo → dns-tcp → tls → http) and stops at the first that produces a definitive verdict; if the chosen method differs, the underlying evidence differs too. Most often this is because the path PMTU on one vantage is below 1500 B, so the natural Echo Reply is already fragmented and the icmp6-echo method falls through to a TCP-based one. This is largely a measurement artifact, not a destination-behaviour difference.
Failure detail — what to grep in your logs
| vantage | our source | your target | method | result | tested (UTC) |
|---|---|---|---|---|---|
| go6lab | 2a00:8642:42::75 | 2a00:1be0:85:69:40:: | icmp6-echo | honored | 2026-05-30T12:42:20Z |
| karsolink | 2a12:d8c0:105a:9001::a154 | 2a00:1be0:85:69:40:: | tls | partial | 2026-05-30T12:44:40Z |
| odin | 2607:fae0:a000::42 | 2a00:1be0:85:69:40:: | icmp6-echo | honored | 2026-05-30T12:42:12Z |
Attempt log (go6lab):
icmp6-echo→ honored (size_before=1460, size_after=None)dns-tcp→ no_tcp: connect failed: timed outtls→ not_honored (size_before=2856, size_after=2856)http→ inconclusive (size_before=219, size_after=None): natural max segment 219B already <= 1220B; nothing to shrink
Attempt log (karsolink):
icmp6-echo→ no_echo: no Echo Reply to 1300-byte probedns-tcp→ no_tcp: connect failed: timed outtls→ partial (size_before=2856, size_after=1937)http→ inconclusive (size_before=200, size_after=None): natural max segment 200B already <= 1220B; nothing to shrink
Attempt log (odin):
icmp6-echo→ honored (size_before=1460, size_after=None)dns-tcp→ no_tcp: connect failed: timed outtls→ not_honored (size_before=2856, size_after=3365)http→ inconclusive (size_before=200, size_after=None): natural max segment 200B already <= 1220B; nothing to shrink
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
Mixed disagreement. At least one pair of vantages used the same probe method and disagreed (real Type 2 asymmetry); other pairs used different methods (probe-availability noise). The path-divergence summary below covers all pairs; the AI interpretation focuses on the real cases.
Per-vantage probe + verdict (headline):
- go6lab: probe
icmp6-echo→ verdicthonored - karsolink: probe
tls→ verdictpartial - 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 | not_honored | inconclusive |
| karsolink | no_echo | no_tcp | partial | inconclusive |
| odin | honored | no_tcp | not_honored | inconclusive |
✓ 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): AS12874, AS21034, AS50673.
- From go6lab (open/Type-2=honored) the path enters AS12874 at hop 8; from karsolink (open/Type-2=partial) the same hop is in AS21034. Last common AS: AS21034. 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 4; from odin (open/Type-2=honored) the same hop is in AS51988. Last common AS: AS21034. The disagreement is most likely rooted in one of those two transit ASes.
- From karsolink (open/Type-2=partial) the path enters AS12874 at hop 5; from odin (open/Type-2=honored) the same hop is in AS3303. Last common AS: AS21034. 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 | 2001:7f8:46:0:1::3303 | AS51988 | ARNES-SIX - ARNES, SI | ✓ honored |
| 5 | 2001:918:100:74::1 | AS3303 | SWISSCOM - Swisscom (Schweiz) AG, CH | ? no_response |
| 6 | 2001:4d98:a000::15d | - | NA | ? no_response |
| 7 | 2001:b00:1:1:1::1b5 | AS12874 | FASTWEB - Fastweb SpA, IT | ? no_response |
| 8 | 2001:b00:1:1:2::ab | AS12874 | FASTWEB - Fastweb SpA, IT | ? no_response |
| 9 | 2001:b00:1:1:2::db | AS12874 | FASTWEB - Fastweb SpA, IT | ? no_response |
| 10 | 2a00:1be0:0:97::257 | AS21034 | MICSO-SRL-AS - Micso Information Technol | ? no_response |
| 11 | * | - | - (no IP) | |
| 12 | * | - | - (no IP) | |
| 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 | 0.8ms | 0% | AS203993 | STEFFANN-DC-AS - S.J.M. Steffann, NL |
| 2 | * | - | 0%* | - | |
| 3 | 2a00:1ca8:1::194 | 2.4ms | 0% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 4 | 2a03:3f40::10:33 | 5.6ms | 0% | AS50673 | Serverius-as - Serverius Holding B.V., NL |
| 5 | 2001:7f8:1::a501:2874:1 | 89.1ms | 0% | - | NA |
| 6 | 2001:b00:1:1:3::131 | 20.8ms | 0% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 7 | 2001:b00:1:1:3::d7 | 31.8ms | 0% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 8 | 2001:b00:1:1:2::d9 | 32.1ms | 50% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 9 | 2a00:1be0:0:97::257 | 37.3ms | 0% | AS21034 | MICSO-SRL-AS - Micso Information Technology Srl, IT |
| 10 | * | - | 0% | - | |
| 11 | * | - | 0% | - | |
| 12 | * | - | - | - | |
| 13 | * | - | - | - | |
| 14 | * | - | - | - | |
| 15 | * | - | - | - | |
| 16 | * | - | - | - | |
| 17 | * | - | - | - | |
| 18 | * | - | - | - | |
| 19 | * | - | - | - | |
| 20 | * | - | - | - | |
| 21 | * | - | - | - | |
| 22 | * | - | - | - | |
| 23 | * | - | - | - | |
| 24 | * | - | - | - |
Rate-limited ICMPv6: hop 8 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).
tracepath -6
1?: [LOCALHOST] 0.030ms pmtu 1500
1: 2a00:8642:42::3 1.807ms
1: 2a00:8642:42::3 1.694ms
2: no reply
3: 2a00:1ca8:1::194 4.055ms
4: 2a03:3f40::10:33 8.497ms
5: 2001:7f8:1::a501:2874:1 64.174ms
6: 2001:b00:1:1:3::133 21.812ms
7: 2001:b00:1:1:3::d7 30.468ms
8: 2001:b00:1:1:2::db 29.849ms
9: 2a00:1be0:0:97::257 40.913ms
10: no reply
11: no reply
12: no reply
13: no reply
14: no reply
15: no reply
16: no reply
17: no reply
18: no reply
19: no reply
20: no reply
21: no reply
22: no reply
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 | * | - | - | - | |
| 3 | * | - | 90% | - | |
| 4 | fastweb.minap.it 2001:7f8:c5::a501:2874:1 | 10.8ms | 30% | AS12874 | Fastweb S.p.A. |
| 5 | 2001:b00:1:1:1::1af | 9.6ms | 0% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 6 | 2001:b00:1:1:3::d7 | 17.8ms | 0% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 7 | 2001:b00:1:1:2::d9 | 18.4ms | 20% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 8 | 2a00:1be0:0:97::257 | 22.3ms | 0% | AS21034 | MICSO-SRL-AS - Micso Information Technology Srl, IT |
| 9 | * | - | 0% | - | |
| 10 | * | - | 0% | - | |
| 11 | * | - | - | - | |
| 12 | * | - | - | - | |
| 13 | * | - | - | - | |
| 14 | * | - | - | - | |
| 15 | * | - | - | - | |
| 16 | * | - | - | - | |
| 17 | * | - | - | - | |
| 18 | * | - | - | - | |
| 19 | * | - | - | - | |
| 20 | * | - | - | - | |
| 21 | * | - | - | - | |
| 22 | * | - | - | - | |
| 23 | * | - | - | - | |
| 24 | * | - | - | - |
Rate-limited ICMPv6: hop 3, hop 4, hop 7 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).
tracepath -6
1?: [LOCALHOST] 0.029ms pmtu 1500
1: karsolink-01.net.karsolink.com 0.725ms
1: karsolink-01.net.karsolink.com 0.786ms
2: 2a12:d8c0:109f:121::a1 1.278ms
3: 2a12:d8c0:101f:6::1 10.614ms
4: no reply
5: 2001:b00:1:1:1::1b1 10.000ms
6: 2001:b00:1:1:3::d7 18.257ms
7: 2001:b00:1:1:2::db 22.173ms
8: 2a00:1be0:0:97::257 23.882ms
9: no reply
10: no reply
11: no reply
12: no reply
13: no reply
14: no reply
15: no reply
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17: no reply
18: no reply
19: no reply
20: no reply
21: no reply
22: no reply
23: no reply
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 | 0.3ms | 0%* | AS8038 | 6CONNECT - 6connect, Inc., US |
| 2 | * | - | - | - | |
| 3 | * | - | 80% | - | |
| 4 | 2001:7f8:46:0:1::3303 | 7.9ms | 0% | AS51988 | ARNES-SIX - ARNES, SI |
| 5 | 2001:918:100:74::1 | 7.9ms | 0% | AS3303 | SWISSCOM - Swisscom (Schweiz) AG, CH |
| 6 | 2001:4d98:a000::15d | 8.8ms | 90% | - | NA |
| 7 | 2001:b00:1:1:1::1b5 | 10.2ms | 0% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 8 | 2001:b00:1:1:2::ab | 22.5ms | 0% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 9 | 2001:b00:1:1:2::db | 27.5ms | 50% | AS12874 | FASTWEB - Fastweb SpA, IT |
| 10 | 2a00:1be0:0:97::257 | 29.4ms | 0% | AS21034 | MICSO-SRL-AS - Micso Information Technology Srl, IT |
| 11 | * | - | 0% | - | |
| 12 | * | - | 0% | - | |
| 13 | * | - | - | - | |
| 14 | * | - | - | - | |
| 15 | * | - | - | - | |
| 16 | * | - | - | - | |
| 17 | * | - | - | - | |
| 18 | * | - | - | - | |
| 19 | * | - | - | - | |
| 20 | * | - | - | - | |
| 21 | * | - | - | - | |
| 22 | * | - | - | - | |
| 23 | * | - | - | - | |
| 24 | * | - | - | - |
Rate-limited ICMPv6: hop 3, hop 6, hop 9 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).
tracepath -6
1?: [LOCALHOST] 0.039ms pmtu 1500
1: fw1-lju.6connect.com 3.023ms
1: fw1-lju.6connect.com 1.089ms
2: no reply
3: no reply
4: 2001:7f8:46:0:1::3303 8.337ms
5: 2001:918:100:74::1 8.271ms
6: 2001:4d98:a000::119 24.667ms asymm 11
7: 2001:b00:1:1:3::131 10.751ms asymm 9
8: 2001:b00:1:1:2::ab 19.147ms asymm 10
9: 2001:b00:1:1:2::db 26.215ms asymm 11
10: 2a00:1be0:0:97::257 29.879ms
11: no reply
12: no reply
13: no reply
14: no reply
15: no reply
16: no reply
17: no reply
18: no reply
19: no reply
20: no reply
21: no reply
22: no reply
23: no reply
24: no reply
Too many hops: pmtu 1500
Resume: pmtu 1500