AS41849 NETSTORMING-WHL-AS NETSTORMING S.R.L.

AS overview

Test target: 2a01:7140::6 · ns008ns.whl.it · address space: PA · prefixes announced: 1

prefix(es): 2a01:7140::/32

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)
Target IP / hostname	Source	ping	1500B	:80	:443	reached	ping	1500B	:80	:443	reached	ping	1500B	:80	:443	reached
`2a01:7140::4` zeus.whl.it	NS	✓	✓	?	?	✓	✓	✓	refused	refused	✓	✓	✓	refused	refused	✓
`2a01:7140::6` ns008ns.whl.it	NS	✓	✓	?	?	✓	✓	✓	refused	refused	✓	✓	✓	refused	refused	✓

RPKI & ASPA

1 of 1 prefix(es) covered by a valid ROA.

Prefix	RPKI state	Reason	Covering VRP(s)
`2a01:7140::/32`	✓ valid	matched VRP (correct origin, length within maxLength)	AS41849 /32 maxLen 32 (ripe)

Random-IP probe (yarrp) into the AS' prefixes

At least one router inside AS41849's announced prefix replied during the random-target probe. Hop(s): 2a01:7140:c::33, 2a01:7140:d::34, 2a01:7140:f:1235::49, 2a01:7140:f::f1cb. 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 to 1300-byte probe. (ICMPv6 Echo + forged PTB)
SLO host (6connect): Type 2 honored. Forged PTB accepted; next response shrunk. (ICMPv6 Echo + forged PTB)

Why they disagree - reachability mismatch: One vantage couldn't drive a flow at all to this destination (no Echo Reply or no responding TCP port), so the active test had no behavioural change to observe. The other vantage's verdict is the only meaningful one here.

Failure detail — what to grep in your logs

vantage	our source	your target	method	result	tested (UTC)
go6lab	`2a00:8642:42::75`	`2a01:7140::6`	`icmp6-echo`	honored	2026-05-30T12:43:06Z
karsolink	`2a12:d8c0:105a:9001::a154`	`2a01:7140::6`	`icmp6-echo`	no_echo	2026-05-30T12:46:56Z
odin	`2607:fae0:a000::42`	`2a01:7140::6`	`icmp6-echo`	honored	2026-05-30T12:42:57Z

Attempt log (go6lab):

icmp6-echo → honored (size_before=1460, size_after=None)
dns-tcp → inconclusive (size_before=156, size_after=None): max DNS-over-TCP segment 156B; not big enough to test PMTU shrink
tls → no_tcp: TLS connect failed
http → no_tcp: tcp/80 not open

Attempt log (karsolink):

icmp6-echo → no_echo: no Echo Reply to 1300-byte probe
dns-tcp → inconclusive (size_before=175, size_after=None): max DNS-over-TCP segment 175B; not big enough to test PMTU shrink
tls → no_tcp: TLS connect failed
http → no_tcp: tcp/80 not open

Attempt log (odin):

icmp6-echo → honored (size_before=1460, size_after=None)
dns-tcp → inconclusive (size_before=175, size_after=None): max DNS-over-TCP segment 175B; not big enough to test PMTU shrink
tls → no_tcp: TLS connect failed
http → 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 → verdict honored
karsolink: probe icmp6-echo → verdict no_echo
odin: probe icmp6-echo → verdict honored

Full per-method matrix (all four methods run at each vantage):

vantage	icmp6-echo	dns-tcp	tls	http
go6lab	honored	inconclusive	no_tcp	no_tcp
karsolink	no_echo	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): AS25091, AS50673, AS6939.

From go6lab (open/Type-2=honored) the path enters an opaque hop at hop 8; from karsolink (open/Type-2=no_echo) the same hop is in AS25091. Last common AS: AS41849. 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 AS6939. Last common AS: AS41849. The disagreement is most likely rooted in one of those two transit ASes.
From karsolink (open/Type-2=no_echo) the path enters AS25091 at hop 9; from odin (open/Type-2=honored) the same hop is in AS41849. Last common AS: AS41849. 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

An operator-targeted diagnostic interpretation can be generated for this AS on demand. The pipeline holds the raw verdicts and the per-hop walk; an AI pass synthesises where to start looking. Click the button below to run it.

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	2001:470:1:5be::1	AS6939	HURRICANE - Hurricane Electric LLC, US	? no_response
5	*	-		- (no IP)
6	2001:470:0:2ea::2	AS6939	HURRICANE - Hurricane Electric LLC, US	? no_response
7	*	-		- (no IP)
8	2001:7f8:c0::4:1071:1	-	NA	? no_response
9	2a01:7140:f::f1cb	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L.,	✓ honored
10	*	-		- (no IP)
11	2a01:7140:c::33	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L.,	? no_response
12	2a01:7140::6	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L.,	✓ honored

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

4/4

Echo small (56B) 26.1ms

4/4

Echo 1500B (DF) 26.2ms

yes

Type 1 dest-unreach

TCP responds on

Path (traceroute + mtr + PTR)

#	IP / PTR	RTT	mtr loss	AS	AS holder
1	2a00:8642:42::3	1.4ms	0%	AS203993	STEFFANN-DC-AS - S.J.M. Steffann, NL
2	gw.friends.steffann.nl 2a00:8642:1000:f000::1	1.9ms	0%*	AS203993	STEFFANN-DC-AS - S.J.M. Steffann, NL
3	2a00:1ca8:1::194	3.0ms	0%	AS50673	Serverius-as - Serverius Holding B.V., NL
4	2a03:3f40::10:41	2.5ms	0%	AS50673	Serverius-as - Serverius Holding B.V., NL
5	*	-	70%	-
6	*	-	80%	-
7	be245.er01.fra01.de.ip-max.net 2a02:2528:2:37::193	11.1ms	20%	AS25091	IP-Max - IP-Max SA, CH
8	*	-	60%	-
9	te0-0-2-0.er01.lug01.ch.ip-max.net 2a02:2528:1602:7::2	22.4ms	10%	AS25091	IP-Max - IP-Max SA, CH
10	2a02:2528:203:12::86	21.7ms	0%	AS25091	IP-Max - IP-Max SA, CH
11	2a01:7140:f:1235::49	26.3ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
12	gw-v6-25-gi0-1.netstorming.net 2a01:7140:d::34	35.1ms	50%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
13	gw-v6-STAR-TE1-1-4.mil2.netstorming.net 2a01:7140:c::33	27.0ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
14	ns008ns.netstorming.net 2a01:7140::6	26.6ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT

Rate-limited ICMPv6: hop 5, hop 6, hop 7, hop 8, hop 9, hop 12 (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                                       2.083ms 
 1:  2a00:8642:42::3                                       1.881ms 
 2:  gw.friends.steffann.nl                                2.985ms 
 3:  2a00:1ca8:1::194                                      3.346ms 
 4:  2a03:3f40::10:41                                      2.911ms 
 5:  no reply
 6:  no reply
 7:  be245.er01.fra01.de.ip-max.net                       13.176ms asymm  5 
 8:  no reply
 9:  te0-0-2-0.er01.lug01.ch.ip-max.net                   22.571ms asymm  7 
10:  2a02:2528:203:12::86                                 21.985ms asymm  8 
11:  2a01:7140:f:1235::49                                 26.830ms asymm 12 
12:  no reply
13:  gw-v6-STAR-TE1-1-4.mil2.netstorming.net              27.035ms asymm 14 
14:  ns008ns.netstorming.net                              26.942ms reached
     Resume: pmtu 1500 hops 14 back 15

From ITA host (Karsolink) open

filter likely at: (none) · min PMTU on path: 1500

4/4

Echo small (56B) 18.8ms

4/4

Echo 1500B (DF) 19.0ms

yes

Type 1 dest-unreach

443,80

TCP responds on

Path (traceroute + mtr + PTR)

#	IP / PTR	RTT	mtr loss	AS	AS holder
1	karsolink-01.net.karsolink.com 2a12:d8c0:105a:9001::1	0.4ms	0%*	AS204471	KARSOLINK - 2S Computers SRL, IT
2	2a12:d8c0:109f:121::a1	0.3ms	0%*	AS204471	KARSOLINK - 2S Computers SRL, IT
3	2a12:d8c0:109f:106::a2	3.1ms	0%	AS204471	KARSOLINK - 2S Computers SRL, IT
4	ipmax.topix.it 2001:7f8:23:ffff::31	19.5ms	0%	-	NA
5	*	-	-	-
6	*	-	10%	-
7	te0-0-1-0.er01.gva17.ip-max.net 2a02:2528:2:28::2	21.7ms	0%	AS25091	IP-Max - IP-Max SA, CH
8	te0-0-1-0.er01.lug01.ch.ip-max.net 2a02:2528:2:45::215	28.5ms	0%	AS25091	IP-Max - IP-Max SA, CH
9	2a02:2528:203:12::86	27.6ms	0%	AS25091	IP-Max - IP-Max SA, CH
10	2a01:7140:f:1235::49	18.6ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
11	gw-v6-25-gi0-1.netstorming.net 2a01:7140:d::34	19.0ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
12	gw-v6-STAR-TE1-1-4.mil2.netstorming.net 2a01:7140:c::33	19.1ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
13	ns008ns.netstorming.net 2a01:7140::6	19.0ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT

Rate-limited ICMPv6: hop 6 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).

tracepath -6

 1?: [LOCALHOST]                        0.032ms pmtu 1500
 1:  karsolink-01.net.karsolink.com                        1.359ms 
 2:  no reply
 3:  2a12:d8c0:109f:106::a2                                3.960ms 
 4:  ipmax.topix.it                                       20.590ms asymm  6 
 5:  no reply
 6:  no reply
 7:  te0-0-1-0.er01.gva17.ip-max.net                      23.275ms asymm  9 
 8:  te0-0-1-0.er01.lug01.ch.ip-max.net                   28.848ms asymm 10 
 9:  2a02:2528:203:12::86                                 28.844ms asymm 11 
10:  2a01:7140:f:1235::49                                 18.512ms asymm  7 
11:  gw-v6-25-gi0-1.netstorming.net                       21.849ms asymm  8 
12:  gw-v6-star-te1-1-4.mil2.netstorming.net              20.017ms asymm  9 
13:  ns008ns.netstorming.net                              19.057ms reached
     Resume: pmtu 1500 hops 13 back 10

From SLO host (6connect) openRFC 4890 ✓

filter likely at: (none) · min PMTU on path: 1500

4/4

Echo small (56B) 20.4ms

4/4

Echo 1500B (DF) 20.2ms

yes

Type 1 dest-unreach

443,80

TCP responds on

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	*	-	0%*	-
3	*	-	90%	-
4	e0-1.core1.lju1.he.net 2001:470:1:5be::1	2.2ms	0%	AS6939	HURRICANE - Hurricane Electric LLC, US
5	*	-	-	-
6	port-channel1.core1.zag2.he.net 2001:470:0:2ea::2	4.1ms	10%	AS6939	HURRICANE - Hurricane Electric LLC, US
7	*	-	-	-
8	2001:7f8:c0::4:1071:1	12.8ms	0%	-	NA
9	gw-v6-60x-gi0-22.mil2.netstorming.net 2a01:7140:f::f1cb	19.4ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
10	*	-	70%	-
11	gw-v6-STAR-TE1-1-4.mil2.netstorming.net 2a01:7140:c::33	20.1ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT
12	ns008ns.netstorming.net 2a01:7140::6	20.4ms	0%	AS41849	NETSTORMING-WHL-AS - NETSTORMING S.R.L., IT

Rate-limited ICMPv6: hop 3, hop 6, hop 10 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).

tracepath -6

 1?: [LOCALHOST]                        0.035ms pmtu 1500
 1:  fw1-lju.6connect.com                                  0.569ms 
 1:  fw1-lju.6connect.com                                  0.469ms 
 2:  ccr-to-fw-ccr1-gw-lju.6connect.com                    0.710ms 
 3:  2a03:a100:0:201:1::1                                  0.738ms 
 4:  e0-1.core1.lju1.he.net                                2.170ms 
 5:  no reply
 6:  port-channel1.core1.zag2.he.net                       4.213ms 
 7:  no reply
 8:  2001:7f8:c0::4:1071:1                                12.794ms 
 9:  gw-v6-60x-gi0-22.mil2.netstorming.net                19.693ms asymm 12 
10:  no reply
11:  gw-v6-STAR-TE1-1-4.mil2.netstorming.net              20.136ms asymm 14 
12:  ns008ns.netstorming.net                              20.276ms reached
     Resume: pmtu 1500 hops 12 back 15