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How I found caching CDNs had been throttling my on a regular basis searching – Diary of a SysAdmin

How I found caching CDNs had been throttling my on a regular basis searching – Diary of a SysAdmin

2023-11-23 06:15:09

My ISP has by no means been wonderful…

Looking the Web was getting worse and worse, however too unpredictable to see a transparent sample. Velocity assessments had been wonderful, many web sites loaded completely, however sufficient didn’t work, so it was value investigating. Apple TV+ would crap out, however provided that casting through AirPlay. BBC Information wouldn’t load in any respect, however iPlayer would slowly.

The community

I’ve a VDSL2 line, Ubiquiti Wi-Fi and normal Catalyst switches. Nothing too bizarre. I pay for a /29 block, so I’ve a number of usable IP addresses. Sure I host my very own mail, and sure, I do DKIM, DMARC and SPF, and MXToolbox exhibits I’m not on any blocklists.

The signs

Working Not working
most web sites load wonderful
however many by no means
800Mbps iperf throughout the LAN
Steady 39 Mbps down / 7 Mbps up
Steady 6ms ping to
PPP is steady and never dropping
AirPlay to LG TV works (through a Unifi AP) however crashes as soon as per present
AirPlay to LG TV works (TV wired in) nonetheless crashes
Spotify can stream to a Bose Soundbar however altering music takes 30sec+
DNS is ok
iOS app downloads take 3min to start out
Swapping Cisco VDSL2 router for the ISP’s router makes some websites now work however not all websites

The trigger

The freebie ISP router has IPv6 enabled by default, so would converse to the CDNs from the clear v6 vary. When utilizing my gear with out IPv6 configured, I can solely converse on the IPv4 vary that’s “shadow banned”.

Proving my principle

Step 1: VPN egress traversing dangerous ISP’s community

I arrange a WireGuard tunnel to a different website I’ve within the Isle of Man, equipped by one other ISP. I forwarded all site visitors from my workstation through this tunnel:

I now come out within the Isle of Man:

through ASN 42455’s community ( to check):

and may surf and stream as regular:

Step 2: Wireshark deep-dive

I took two captures of my workstation visiting in Chrome. The primary with out the WireGuard tunnel on, and the second with it on. Let’s take a look at tcp site visitors:

With out WireGuard:

Screen capture of WireShark showing no meaningful TCP traffic making it through
No significant TCP site visitors makes it out. Lots of retransmissions and duplicate ACKs are taking place

With WireGuard:

Screen capture of WireShark when the WireGuard VPN is running to the Isle of Man site, showing lots of TCP traffic passing
A pleasant wholesome TCP session

(I disabled checksum verification within the screenshots above, as I’m capturing on the identical machine having issues, which additionally has checksum offloading on the NIC.)

Zen Broadband, my ISP (for now)

I’ll save my views on Zen for when this case is resolved. I’ve obtained up to now by way of the help course of I’m now coping with their Community Ops staff to research this. They’ll nonetheless redeem themselves by merely giving me a distinct /29 block as far-off from as potential 🙂

See Also

Be extra particular. What do you imply by “throttled”?

The blocking is nondeterministic. While Akamai (who provides a popularity verify) returns one in all my IPs as clear, web sites of their clients like eBay have proven the throttling behaviour. Apple TV+ seems to be served by Akamai too (, which has been the worst offender for “throttling” my streaming:

PS C:WINDOWSsystem32> nslookup
Server:  dc1-lon.core.*********.web
Tackle:  10.*.*.*

Non-authoritative reply:
Title:    e673.dsce9.akamaiedge.web
Addresses:  2a02:26f0:fd00:1088::2a1


It’s additionally accessible with IPv6, explaining the freebie ISP router principle.

Fastly doesn’t provide a rep verify on their web site however proper now received’t load in any respect. Cloudflare is opaque too about disclosing what IPs they’re throttling.

Why would a spread get throttled or “shadow banned”?

That is extraordinarily tough to reply and I’ve no good principle. The identical IP vary handles my electronic mail and I typically haven’t any bother emailing main suppliers like Gmail, Outlook, Yahoo!, and plenty of different counterparties.

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