A quick glance at longer than /24 IPv4 prefixes

Yesterday RIPE Labs announced a new test to measure propagation of longer than /24 IPv4 prefixes. The scope of these prefixes is to allow small allocations from the 23.128/10 net block that ARIN reserved to facilitate IPv6 deployment, but it could be impaired by filters and routing policies commonly deployed all around the net.

While looking forward to the RIPE results I couldn’t help glancing at the current situation as seen by a bunch of RIPE Atlas probes, so I performed some small tests on my own.


The measurements I created are based on 500 random probes from the world wide area and have been used to ping the IP addresses announced by RIPE RIS (AS12654); these IP addresses are split in 2 main groups: one group has 3 addresses each one from a prefix (/24, /25 and /28) with a registered route object, the other group has similar addresses but from prefixes without a registered route object.

Prefix            Pingable IP	 Route object?	My Atlas measurement ID    yes            1767799    yes            1767800  yes            1767801   no             1767802   no             1767803 no             1767804

All measurements use the same set of probes, taken from the first measurement (the /24 prefix with registered route object).

Of course, mine is only a partial view (500 probes) taken from a bigger partial view (all the RIPE Atlas probes) of the global Internet; please take my results with regard of this.


Data collected by RIPE Atlas have been parsed with a small python script that I used to match the results. It uses the RIPE Atlas Sagan library.


From the first 3 measurements, 497 probes received at least one response from the /24 prefix with the registered route object; of those, only 57 received responses from the /25 prefix and 41 from the /28 prefix too.

Also 497 probes received responses from the /24 prefix without the registered route object; of those, 52 received responses from the /25 prefix and 38 from the /28 prefix too.

Longer than 24 prefixes reachability


For those probes which reach the /25 and the /28 prefix the average RTT seems to be pretty stable regardless of the prefix size.

Longer than 24 prefixes with route object  RTT avg

Longer than 24 prefixes without route object  RTT avg

Probes distribution

Here it is:

Distribution of probes which reached the /25 prefix with registered route object

Distribution of probes which reached the /25 prefix with registered route object – Click to enlarge

More and deeper tests may be useful to reveal AS paths and peering/transit relationships impacts on these measurements; maybe I’ll blog another post as soon as possible, or – better yet – maybe RIPE Labs folks will write about them in their results.


As far as I can see from the measurements I run (based on a small sample of probes), reachability of smaller than /24 prefixes is almost unaffected by the presence of registered route objects; who receives the registered net also receives the unregistered one. From the performances point of view, when the smaller prefixes are reached, RTTs are not better nor worse than /24 prefixes.

The real question is: what’s the portion of Internet that right now succeed to reach these prefixes?

I guess that some efforts will be needed in order to have ISPs to review their routing policies and accept the new small prefixes from the reserved pool.


RIPE Labs, Propagation of Longer-than-/24 IPv4 Prefixes – https://labs.ripe.net/Members/emileaben/propagation-of-longer-than-24-ipv4-prefixes

ARIN, Policy Proposal 2008-5 – Dedicated IPv4 block to facilitate IPv6 deployment- https://www.arin.net/policy/proposals/2008_5.html

ARIN, Number Resource Policy Manual (NRPM), adoption of Dedicated IPv4 block to facilitate IPv6 Deployment – https://www.arin.net/policy/nrpm.html#four10

ARIN, announcement of reservation – https://www.arin.net/announcements/2014/20140130.html

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Italian, born in 1980, I started working in the IT/telecommunications industry in the late '90s; I'm now a system and network engineer with a deep knowledge of the global Internet and its core architectures, and a strong focus on network automation.

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