AS200036 CityNet Niccolo Pietrobon

IPv6 prefix announced, but nothing inside is responding yet. AS200036 announces 1 IPv6 prefix(es) to the global routing table - that’s the part that BGP and our route-server scrape confirm. But our active discovery (curated hostnames, holder-derived domains, authoritative DNS NS/SOA/MX, certificate-transparency hostnames, RIPE Atlas, RDAP, IPv6 Hitlist) found no ICMPv6-responsive host inside the prefix on either vantage, and a yarrp pass against random addresses inside the prefix produced zero in-prefix hops (no router on the path through the AS replied with Time-Exceeded for any random target). That combination usually means the announcement is configured but the addresses inside aren’t in active use yet. The BGP route is there; the operational deployment is still ahead.

AS overview

Test target: 2a12:d8c6::1 · (no live host found) · address space: unknown · prefixes announced: 1

prefix(es): 2a12:d8c6::/32

RPKI & ASPA

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

Prefix	RPKI state	Reason	Covering VRP(s)
`2a12:d8c6::/32`	✓ valid	matched VRP (correct origin, length within maxLength)	AS200036 /32 maxLen 32 (ripe)

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

We probed 15 arbitrary IPv6 address(es) inside AS200036's announced prefix(es). No router inside the prefix responded. The deepest visible hop was 2a12:d8c0:101f:5::2 at hop 8 - that router answers ICMPv6 Echo. This is not in AS200036's announced prefix; operationally it's the AS-edge / peering interface (often on an IXP 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

Type 2 active test inconclusive: no Echo Reply to 1300-byte probe.
method: ICMPv6 Echo + forged PTB, tested 2026-05-25T12:38:33Z

Failure detail — what to grep in your logs

vantage	our source	your target	method	result	tested (UTC)
go6lab	`2a00:8642:42::75`	`2a12:d8c6::1`	`icmp6-echo`	no_echo	2026-05-25T12:38:33Z
karsolink	`2a12:d8c0:105a:9001::a154`	`2a12:d8c6::1`	`icmp6-echo`	no_echo	2026-05-25T12:50:54Z
odin	`2607:fae0:a000::42`	`2a12:d8c6::1`	`icmp6-echo`	no_echo	2026-05-25T12:38:02Z

Attempt log (go6lab):

icmp6-echo → no_echo: no Echo Reply to 1300-byte probe
dns-tcp → no_tcp: connect failed: timed out
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 → no_tcp: connect failed: timed out
tls → no_tcp: TLS connect failed
http → no_tcp: tcp/80 not open

Attempt log (odin):

icmp6-echo → no_echo: no Echo Reply to 1300-byte probe
dns-tcp → no_tcp: connect failed: timed out
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.

From NL host (go6lab) transit only unreachable

filter likely at: past AS204471 (KARSOLINK) · min PMTU on path: 1500

0/4

Echo small (56B) -

0/4

Echo 1500B (DF) -

Type 1 dest-unreach

TCP responds on

Path (traceroute + mtr + PTR)

#	IP / PTR	RTT	mtr loss	AS	AS holder
1	2a00:8642:42::3	1.3ms	0%	AS203993	STEFFANN-DC-AS - S.J.M. Steffann, NL
2	gw.friends.steffann.nl 2a00:8642:1000:f000::1	2.3ms	0%*	AS203993	STEFFANN-DC-AS - S.J.M. Steffann, NL
3	2a00:1ca8:1::194	2.2ms	0%	AS50673	Serverius-as - Serverius Holding B.V., NL
4	2a03:3f40::10:41	2.6ms	0%	AS50673	Serverius-as - Serverius Holding B.V., NL
5	speed-ix.fibertelecom.it 2001:7f8:b7::a504:1327:1	4.2ms	0%	-	NA
6	2a03:b020::226	20.1ms	0%	AS41327	FIBERTELECOM-AS - Fiber Telecom S.p.A., IT
7	2a03:b020:1:51::b	19.9ms	0%	AS41327	FIBERTELECOM-AS - Fiber Telecom S.p.A., IT
8	2a12:d8c0:101f:5::2	23.5ms	0%	AS204471	KARSOLINK - 2S Computers SRL, IT
9	*	-	-	-
10	*	-	-	-
11	*	-	-	-
12	*	-	-	-
13	*	-	-	-
14	*	-	-	-
15	*	-	-	-
16	*	-	-	-
17	*	-	-	-
18	*	-	-	-
19	*	-	-	-
20	*	-	-	-
21	*	-	-	-
22	*	-	-	-
23	*	-	-	-
24	*	-	-	-

tracepath -6

 1?: [LOCALHOST]                        0.052ms pmtu 1500
 1:  2a00:8642:42::3                                       1.801ms 
 1:  2a00:8642:42::3                                       1.909ms 
 2:  gw.friends.steffann.nl                                2.213ms 
 3:  2a00:1ca8:1::194                                      2.798ms 
 4:  2a03:3f40::10:41                                      2.769ms 
 5:  speed-ix.fibertelecom.it                              4.441ms asymm  3 
 6:  2a03:b020::226                                       20.776ms asymm  4 
 7:  2a03:b020:1:51::b                                    21.038ms asymm  5 
 8:  2a12:d8c0:101f:5::2                                  24.181ms asymm  6 
 9:  no reply
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     Too many hops: pmtu 1500
     Resume: pmtu 1500

From ITA host (Karsolink) transit only unreachable

filter likely at: past AS204471 (KARSOLINK) · min PMTU on path: 1500

0/4

Echo small (56B) -

0/4

Echo 1500B (DF) -

Type 1 dest-unreach

TCP responds on

Path (traceroute + mtr + PTR)

#	IP / PTR	RTT	mtr loss	AS	AS holder
1	*	-	0%*	-
2	*	-	0%*	-
3	2a12:d8c0:109f:106::a2	3.3ms	0%	AS204471	KARSOLINK - 2S Computers SRL, IT
4	*	-	-	-
5	*	-	-	-
6	*	-	-	-
7	*	-	-	-
8	*	-	-	-
9	*	-	-	-
10	*	-	-	-
11	*	-	-	-
12	*	-	-	-
13	*	-	-	-
14	*	-	-	-
15	*	-	-	-
16	*	-	-	-
17	*	-	-	-
18	*	-	-	-
19	*	-	-	-
20	*	-	-	-
21	*	-	-	-
22	*	-	-	-
23	*	-	-	-
24	*	-	-	-

tracepath -6

 1?: [LOCALHOST]                        0.032ms pmtu 1500
 1:  karsolink-01.net.karsolink.com                        0.659ms 
 2:  2a12:d8c0:109f:121::a1                                0.804ms 
 3:  2a12:d8c0:109f:106::a2                                3.712ms 
 4:  no reply
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     Too many hops: pmtu 1500
     Resume: pmtu 1500

From SLO host (6connect) transit only unreachable

filter likely at: past AS6939 (HURRICANE) · min PMTU on path: 1500

0/4

Echo small (56B) -

0/4

Echo 1500B (DF) -

Type 1 dest-unreach

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	2a03:a100:0:201:1::1	0.7ms	30%	AS56635	XENYA - XENYA inzeniring, proizvodnja in trgovina, d.o.o. Ljubljana, SI
4	e0-1.core1.lju1.he.net 2001:470:1:5be::1	2.1ms	20%	AS6939	HURRICANE - Hurricane Electric LLC, US
5	*	-	-	-
6	*	-	0%	-
7	*	-	-	-
8	*	-	-	-
9	*	-	-	-
10	*	-	-	-
11	*	-	-	-
12	*	-	-	-
13	*	-	-	-
14	*	-	-	-
15	*	-	-	-
16	*	-	-	-
17	*	-	-	-
18	*	-	-	-
19	*	-	-	-
20	*	-	-	-
21	*	-	-	-
22	*	-	-	-
23	*	-	-	-
24	*	-	-	-

Rate-limited ICMPv6: hop 3, hop 4 (loss between 5% and 95% across mtr cycles - the router replies but only sometimes).

tracepath -6

 1?: [LOCALHOST]                        0.028ms pmtu 1500
 1:  fw1-lju.6connect.com                                  0.593ms 
 1:  fw1-lju.6connect.com                                  0.490ms 
 2:  no reply
 3:  2a03:a100:0:201:1::1                                  1.019ms 
 4:  e0-1.core1.lju1.he.net                                2.090ms 
 5:  no reply
 6:  port-channel1.core1.zag2.he.net                       4.292ms 
 7:  no reply
 8:  no reply
 9:  no reply
10:  no reply
11:  no reply
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     Too many hops: pmtu 1500
     Resume: pmtu 1500