A surprisingly large number of ASNs get assigned by the Internet’s regional registries every month, see table 1. 

Regional RegistryAverage New ASNs/MonthReference
RIPE NCC181https://www.iana.org/numbers/allocations/ripencc/asn/
Table 1. Average New ASNs/Month by Regional Registry

That’s a lot of new ASNs.

Other times, ASNs that have laid dormant for some years may be “reanimated” and suddenly reappear in the routing tables.

While both the brand new ASNs and “newly reanimated” ASNs may be used for totally legitimate purposes by totally legitimate parties, in other cases, those newly-seen ASNs may be staged for insalubrious purposes. Either way, newly seen ASNs may be worth a closer look. Today we’re going to describe how you can easily find those new ASNs.

“So, What Is An ASN? Why Would I Be Interested in ASNs as a Cybersecurity Person?”

An ASN, or Autonomous System Number, is defined as a number assigned to a group of network addresses, managed by a particular network operator, that share a common routing policy. Most ISPs, large corporations, and university networks have an ASN. For example, Google uses AS15169, Sprint uses AS1239, Intel uses AS4983, the University of California at Berkeley uses AS25, DomainTools uses AS17318, and so on. Some large networks with particularly complex routing policies may have more than one ASN; others, with simple routing policies and only a single upstream network provider, may have none (their network blocks are just announced using their upstream provider’s ASN).

Think of an ASN as a number that “maps to” or represents a particular provider or network. As such, it is a useful way to aggregate and sort IP addresses into useful chunks, even though its initial purpose (and continued most important usage) is in conjunction with BGP4 for inter-AS routing of network traffic. 

Some specific examples of cybersecurity uses for ASN data:

Today, however, we just want to focus on how we can find the new ASNs that we haven’t seen before. We’ll snag BGP data from the RouteViews project at the University of Oregon (see https://www.routeviews.org/routeviews/) for this purpose.

Retrieving Routing Data

RouteViews collects data at many different locations worldwide (https://www.routeviews.org/routeviews/index.php/collectors/) so our first decision is, “What collector do I want to look at?” We arbitrarily decided to use data from the collector at Equinix in Virginia. We can see the RIB (routing information base) files for October 2023 for that site at

We can download files by pointing-and-clicking links on that page, or we can use a command line web client such as wget (see
https://www.gnu.org/software/wget/) to retrieve files:

$ wget https://archive.routeviews.org/route-views.eqix/bgpdata/2023.10/RIBS/rib.20231012.1400.bz2

The file we retrieve is compressed with Bzip2 (see https://en.wikipedia.org/wiki/Bzip2) so our first task will be to decompress it with bunzip2:

$ bunzip2 rib.20231012.1400.bz2

Then we can use bgpdump (see https://github.com/RIPE-NCC/bgpdump) to read the decompressed RIB file. Typical entries from the decompressed file output look like:

$ bgpdump -M -v rib.20231012.1400
TABLE_DUMP2|10/12/23 14:00:00|B||57695||57695 60068 174|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||11039||11039|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||19151||19151 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||57695||57695 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||293||293 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||41095||41095 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||199524||199524 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||40934||40934 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||6939||6939 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||6079||6079 13335|IGP
TABLE_DUMP2|10/12/23 14:00:00|B||2914||2914 13335|IGP

We want to focus on just the 7th “vertical bar”-separated column (highlighted above) since it has the ASN path for each prefix. We’ll save the extracted ASNs into a file called dumped_asns.txt:

$ bgpdump -M -v rib.20231012.1400 | awk -F"|" '{print $7}' > dumped_asns.txt

We now need to read and process that data. We’ll do that with a little Python3 program called accumulate-asns.py. It will essentially read the ASN data, split it up, and then add each ASN to a Python3 set if it isn’t already a member, printing out any newly-seen ASNs along the way.

$ cat accumulate-asns.py
import sys

# we save state
oldasns=open("old_asns.txt", "r")
for asns in oldasns:

# we are going to look for new ASNs in this new RIB
for line in sys.stdin:
    asns = line.split(" ")

    for asn in asns:

        for my_as in asn2:

            if my_as not in asn_set:

We can then run that program. The first time we run it, we need to create an empty initial “old_asns.txt” file for our code to “read:”

$ touch old_asns.txt

We can then run our program:

$ cat dumped_asns.txt | ./accumulate-asns.py | sort -n > base-asns.txt

We now have a “base list” of ASNs in base-asns.txt. If you want to save a pristine copy of this file, now’s a good time to do so.

Finding What’s New: First Addition…

New RIB files get saved every two hours. So after a couple of hours we can then run:

$ wget https://archive.routeviews.org/route-views.eqix/bgpdata/2023.10/RIBS/rib.20231012.1600.bz2
$ bgpdump -M -v rib.20231012.1600 | awk -F"|" '{print $7}' > dumped_asns_2.txt
$ cat dumped_asns_2.txt | ./accumulate-asns.py | sort -n > base-asns-new.txt

We then have a list of newly-seen ASNs in base-asns-new.txt  

We’ll update the old_asns.txt file by adding the newly discovered ASNs to it. 

To make it easy for the reader to “grok” the new ASNs interactively here, we manually re-arranged and augmented that list of ASNs with associated provider details from https://bgp.he.net/

20362		VeriSign Global Registry Services
36625		VeriSign Global Registry Services
36631		VeriSign Global Registry Services
396547		VeriSign Global Registry Services
396554		Verisign Global Registry Services

9501		AS number of Chemical & Metallurgical Design Co. Ltd. (PBC) [India]
40006		Tri-County Wireless, LLC [US]
42491		Arpage AG [Switzerland]
49996		Individual entrepreneur Vyacheslav Yuryevich Anisimov [Russia]
60381		Pana Services Ltd [UK]
135500		R Systems International Limited [India]
151531		PT Data Telematika Indonesia [Indonesia]
328353		Methodist University College Ghana [Ghana]

65000		[private ASN]
65555		[reserved ASN]

Getting In the Rhythm: Finding a Second Batch of New ASNs

And a few hours later, a new RIB is available for processing…

$ wget https://archive.routeviews.org/route-views.eqix/bgpdata/2023.10/RIBS/rib.20231012.1800.bz2
$ bunzip2 rib.20231012.1800.bz2
$ bgpdump -M -v rib.20231012.1800 | awk -F"|" '{print $7}' > dumped_asns_3.txt
$ cat dumped_asns_3.txt | ./accumulate-asns.py | sort -n > base-asns-new.txt

33179		Two Monkeys LLC [Sheridan WY]
58249		Sky Dragon Company With Limited Liability [Iran]
64289		Macarne LLC [Sacramento CA]
135740		Netlife Network Pvt Ltd [India]
141611		PT Interkoneksi Dan Komunikasi Indonesia [Indonesia]
216179		Nathaniel Bill [UK]

Once again, we’ll update the old_asns.txt file with our newly discovered ASNs.

And A Third Run

And one last time…

wget https://archive.routeviews.org/route-views.eqix/bgpdata/2023.10/RIBS/rib.20231012.2000.bz2
bunzip2 rib.20231012.2000.bz2
bgpdump -M -v rib.20231012.2000 | awk -F"|" '{print $7}' > dumped_asns_4.txt
cat dumped_asns_4.txt | ./accumulate-asns.py | sort -n > base-asns-new.txt

11913		Elevate Homescriptions [Orem UT]
23398		Dasan Zhone Solutions, Inc. [Plano TX]
35659		GERMAN NETWORK GMBH [Germany]
37085		The Open University of Tanzania [Tanzania]	
131074		APNIC R&D Centre JP [Australia]
131694		PT Jabikha Teknologi Indonesia
150335		Brosis Communication [Bangladesh]
197438		Julius Birkhofen [Germany]
199114		McKesson Europe AG [Germany]
216275		Noerdnet ApS [Denmark]
216381		Axians IT Services AG [Switzerland]
394035		Pac-12 Conferences [San Francisco, CA]
399160		Neustar Security Services [Herndon, VA]

As before, update the old_asns.txt file with our newly discovered ASNs.

Conclusion and Next Steps

You’ve now seen how you can use RouteViews data to find new ASNs as they begin to be used. Where could we take this next?

  • While we ran our sample data manually, it wouldn’t take much imagination to turn that process into a repeatable, automatable procedure.
  • We pulled the data for our monitoring from a single RouteViews collector location, but there are 46 collectors listed at

    Using data from more than one collector might deliver improved visibility for new ASNs, but please retrieve Routeviews data responsibly — don’t pull data if you don’t have the time, system capacity and need for it.
  • Manually augmenting the newly-discovered ASNs with name and location data encourages familiarity with the data, but is (in honesty) somewhat tedious. An automated process would eliminate some of the drudgery associated with that custodial ASN annotation maintenance work.
  • Some ASNs might be of more interest than others — maybe you’re only interested in new ASNs from a conflict region, for example, or maybe you’re an investigator focused only on a particular cyber crime locus. Automatic filtering to support that sort of “fencing” would probably make some people very happy.
  • We focused on discovering newly appearing ASNs, but ASNs may also disappear. Things that stop existing may be as interesting as things that have just started to exist. It might also be cool to graph when ASNs are (and aren’t) seen.
  • ASNs can be mapped to one or more IP address prefixes. IP address prefixes can be mapped to domains using DNSDB. It might be interesting to know what domains are suddenly coming up on brand new ASNs, eh?

Anyhow, we hope you find this an intriguing topic! If you have any questions, please reach out.