| Internet-Draft | JAMES | March 2022 |
| Vyncke, et al. | Expires 21 September 2022 | [Page] |
In 2016, RFC7872 has measured the drop of packets with IPv6 extension headers. This document presents a slightly different methodology with more recent results. It is still work in progress.¶
This note is to be removed before publishing as an RFC.¶
The latest revision of this draft can be found at https://evyncke.github.io/v6ops-james/draft-vyncke-v6ops-james.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-vyncke-v6ops-james/.¶
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In 2016, [RFC7872] has measured the drop of packets with IPv6 extension headers on their transit over the global Internet. This document presents a slightly different methodology with more recent results. Since then, [I-D.draft-ietf-opsec-ipv6-eh-filtering] has provided some recommendations for filtering transit traffic, so there may be some changes in providers policies.¶
It is still work in progress, but the authors wanted to present some results at IETF-113 (March 2022). The code is open source and is available at [GITHUB].¶
In a first phase, the measurement is done between collaborating IPv6 nodes, a.k.a. vantage points, spread over the Internet and multiple Autonomous Systems (ASs). As seen in Section 3.2, the source/destination/transit ASs include some "tier-1" providers per [TIER1], so, they are probably representative of the global Internet core.¶
Relying on collaborating nodes has some benefits:¶
Future phases will send probes to non-collaborating nodes with a much reduced probing speed. The destination will include [ALEXA] top-n websites, popular CDN, as well as random prefix from the IPv6 global routing table. A revision of this IETF draft will describe those experiments.¶
Several servers were used worldwide (albeit missing Africa and China as the authors were unable to find IPv6 servers in these regions). Table 1 lists all the vantage points together with their AS number and country.¶
| ASN | AS Name | Country code | Location |
|---|---|---|---|
| 7195 | Edge Uno | AG | Buenos Aires |
| 12414 | NL-SOLCON SOLCON | NL | Amsterdam |
| 14061 | Digital Ocean | CA | Toronto, ON |
| 14061 | Digital Ocean | USA | New York City, NY |
| 14601 | Digital Ocean | DE | Francfort |
| 14601 | Digital Ocean | IN | Bangalore |
| 14601 | Digital Ocean | SG | Singapore |
| 16276 | OVH | AU | Sydney |
| 16276 | OVH | PL | Warsaw |
| 44684 | Mythic Beasts | UK | Cambridge |
| 47853 | Hostinger | US | Ashville, NC |
| 60011 | MYTHIC-BEASTS-USA | US | Fremont, CA |
| 198644 | GO6 | SI | Ljubljana |
During first phase (traffic among fully-meshed collaborative nodes), Table 2 show the ASs for which our probes have collected data.¶
| AS Number | AS Description | Comment |
|---|---|---|
| 174 | COGENT-174, US | Tier-1 |
| 1299 | TWELVE99 Twelve99, Telia Carrier, SE | Tier-1 |
| 2914 | NTT-COMMUNICATIONS-2914, US | Tier-1 |
| 3320 | DTAG Internet service provider operations, DE | Tier-1 |
| 3356 | LEVEL3, US | Tier-1 |
| 4637 | ASN-TELSTRA-GLOBAL Telstra Global, HK | Regional Tier |
| 4755 | TATACOMM-AS TATA Communications formerly VSNL is Leading ISP, IN | |
| 5603 | SIOL-NET Telekom Slovenije d.d., SI | |
| 6453 | Tata Communication | Tier-1 |
| 6762 | SEABONE-NET TELECOM ITALIA SPARKLE S.p.A., IT | Tier-1 |
| 6939 | HURRICANE, US | Regional Tier |
| 7195 | EDGEUNO SAS, CO | |
| 8447 | A1TELEKOM-AT A1 Telekom Austria AG, AT | |
| 9498 | BBIL-AP BHARTI Airtel Ltd., IN | |
| 12414 | NL-SOLCON SOLCON, NL | |
| 14061 | DIGITALOCEAN-ASN, US | |
| 16276 | OVH, FR | |
| 21283 | A1SI-AS A1 Slovenija, SI | |
| 34779 | T-2-AS AS set propagated by T-2 d.o.o., SI | |
| 44684 | MYTHIC Mythic Beasts Ltd, GB | |
| 60011 | MYTHIC-BEASTS-USA, GB | |
| 198644 | GO6, SI |
The table attributes some tier qualification to some ASs based on the Wikipedia page [TIER1], but there is no common way to decide who is a tier-1. Based on some CAIDA research, all the above (except GO6, which is a stub network) are transit providers.¶
While this document lists some operators, the intent is not to build a wall of fame or a wall of shame but more to get an idea about which kind of providers drop packets with extension headers and how widespread the drop policy is enforced and where, i.e., in the access provider or in the core of the Internet.¶
Comparing the traceroutes with and without extension headers allows the attribution of a packet drop to one AS. But, this is not an easy task as inter-AS links often use IPv6 address of only one AS (if not using link-local per [RFC7704]). This document uses the following algorithm to attribute the drop to one AS for packet sourced in one AS and then having a path traversing AS#foo just before AS#bar:¶
In several cases, the above algorithm was not possible (e.g., some intermediate routers do not generate an ICMP unreachable hop limit exceeded even in the absence of any extension headers), then the drop is not attributed. Please also note that the goal of this document is not to 'point fingers to operators' but more to evaluate the potential impact. I.e., a tier-1 provider dropping packets with extension headers has a much bigger impact on the Internet traffic than an access provider.¶
Future revision of this document will use the work of [MLAT_PEERING].¶
In the first phase among collaborating vantage points, packets always contained either a UDP payload or a TCP payload, the latter is sent with only the SYN flag set and with data as permitted by section 3.4 of [RFC793] (2nd paragraph). A usual traceroute is done with only the UDP/TCP payload without any extension header with varying hop-limit in order to learn the traversed routers and ASs. Then, several UDP/TCP probes are sent with a set of extension headers:¶
hop-by-hop and destination options header containing:¶
In the above, length is the length of the extension header itself except for the fragmentation header where the length is the IP packet length (i.e., including the IPv6, and TCP/UDP headers + payload).¶
For hop-by-hop and destination options headers, when required multiple PadN options were used in order to bypass some Linux kernels that consider a PadN larger than 8 bytes is an attack, see section 5.3 of [BCP220], even if multiple PadN options violates section 2.1.9.5 of [RFC4942].¶
In addition to the above extension headers, other probes were sent with next header field of IPv6 header set to:¶
This section presents the current results out of phase 1 (collaborating vantage points) testing. About 4860 experiments were run, one experiment being defined by sending packets between 2 vantage points with hop-limit varying from 1 to the number of hops between the two vantage points and for all the extension headers described in Section 3.3.¶
Table 3 lists all routing header types and the percentage of experiments that were successful, i.e., packets with routing header reaching their destination:¶
| Routing Header Type | %-age of packets reaching destination |
|---|---|
| 0 | 80.9% |
| 1 | 99.5% |
| 2 | 99.5% |
| 3 | 99.5% |
| 4 | 69.0% |
| 5 | 99.5% |
| 6 | 99.3% |
Table 4 lists the few ASs that drop packets with the routing header type 0 (the original source routing header, which is now deprecated).¶
| AS Number | AS description |
|---|---|
| 6939 | HURRICANE, US |
It is possibly due to a strict implementation of [RFC5095] but it is expected that no packet with routing header type 0 would be transmitted anymore. So, this is not surprising.¶
Table 5 lists the few ASs that drop packets with the routing header type 4 (Segment Routing Header [RFC8754]).¶
| AS Number | AS description |
|---|---|
| 16276 | OVH, FR |
This drop of SRH was to be expected as SRv6 is specified to run only in a limited domain.¶
Other routing header types (1 == deprecated NIMROD [RFC1753], 2 == mobile IPv6 [RFC6275], 3 == RPL [RFC6554], and even 5 == CRH-16 and 6 == CRH-32[I-D.draft-bonica-6man-comp-rtg-hdr]) can be transmitted over the global Internet without being dropped (assuming that the 0.5% of dropped packets are within the measurement error).¶
Many ASs drop packets containing either hop-by-hop options headers per Table 6 below:¶
| Option Type | Length | %-age of packets reaching destination |
|---|---|---|
| Skip | 8 | 5.8% |
| Discard | 8 | 0.0% |
| Skip one large PadN | 256 | 1.9% |
| Skip multiple PadN | 256 | 0.0% |
| Discard | 256 | 0.0% |
| Skip | 512 | 1.9% |
| Discard | 512 | 0.0% |
It appears that hop-by-hop options headers cannot reliably traverse the global Internet; only small headers with 'skipable' options have some chances. If the unknown hop-by-hop option has the 'discard' bits, it is dropped per specification.¶
Many ASs drop packets containing destination options headers per Table 7:¶
| Length | Multiple PadN | %-age of packets reaching destination |
|---|---|---|
| 8 | No | 99.3% |
| 16 | No | 99.3% |
| 32 | No | 93.3% |
| 64 | No | 41.6% |
| 128 | No | 4.5% |
| 256 | No | 2.6% |
| 256 | Yes | 2.6% |
| 512 | No | 2.6% |
The measurement did not find any impact of the discard/skip bits in the destination headers options, probably because the routers do not look inside the extension headers into the options. The use of a single large PadN or multiple 8-octet PadN options does not influence the result.¶
The size of the destination options header has a major impact on the drop probability. It appears that extension header larger than 16 octets already causes major drops. It may be because the 40 octets of the IPv6 header + the 16 octets of the extension header (total 56 octets) is still below some router hardware lookup mechanisms while the next measured size (extension header size of 64 octets for a total of 104 octets) is beyond the hardware limit and some AS has a policy to drop packets where the TCP/UDP ports are unknown...¶
The propagation of two kinds of fragmentation headers was analysed: atomic fragment (offset == 0 and M-flag == 0) and plain first fragment (offset == 0 and M-flag == 1). The Table 8 displays the propagation differences.¶
| M-flag | %-age of packets reaching destination |
|---|---|
| 0 (atomic) | 70.2% |
| 1 | 99.0% |
The size of the overall IP packets (512, 1280, and 1500 octets) does not have any impact on the propagation.¶
Table 9 lists some ASs that do not drop transit traffic (except for routing header type 0) and follow the recommendations of [I-D.draft-ietf-opsec-ipv6-eh-filtering]. This list includes tier-1 transit providers (using the "regional" tag per [TIER1]):¶
| AS Number | AS Description | Comment |
|---|---|---|
| 4637 | ASN-TELSTRA-GLOBAL Telstra Global, HK | Regional Tier |
| 4755 | TATACOMM-AS TATA Communications formerly VSNL is Leading ISP, IN | |
| 21283 | A1SI-AS A1 Slovenija, SI | |
| 60011 | MYTHIC-BEASTS-USA, GB |
Some ASs also drop only large (more than 8 octets) destination options headers, see Table 10:¶
| AS Number | AS Description | Largest Forwarded Dest.Opt. Size |
|---|---|---|
| 6453 | Tata Communication | 8 |
| 1299 | TWELVE99 Twelve99, Telia Carrier, SE | 8 |
| 174 | COGENT-174, US | 8 |
Measurements also include two protocol numbers that are mainly new use of IPv6. Table 11 indicates the percentage of packets reaching the destination.¶
| Next Header | %-age of packets reaching destination |
|---|---|
| NoNextHeader (59) | 99.7% |
| Ethernet (143) | 99.2% |
The above indicates that those IP protocols can be transmitted over the global Internet without being dropped (assuming that the 0.3-0.8% of dropped packets are within the measurement error).¶
While the analysis has areas of improvement (geographical distribution and impact on latency), it appears that:¶
Of course, the next phase of measurement with non-collaborating parties will probably give another view.¶
While active probing of the Internet may be considered as an attack, this measurement was done among collaborating parties and using the probe attribution technique described in [I-D.draft-vyncke-opsec-probe-attribution] to allow external parties to identify the source of the probes if required.¶
This document has no IANA actions.¶
The authors want to thank Sander Steffann and Jan Zorz for allowing the free use of their labs. Other thanks to Fernando Gont who indicated a nice IPv6 hosting provider in South America.¶
Special thanks as well to Professor Benoit Donnet for his support and advices. This document would not have existed without his support.¶