Well, no longer! Today, we are pleased to announce the launch of our self-serve BYOIP API, which enables our customers to onboard and set up their BYOIP prefixes themselves.

With self-serve, we handle the bureaucracy for you. We have automated this process using the gold standard for routing security — the Resource Public Key Infrastructure, RPKI. All the while, we continue to ensure the best quality of service by generating LOAs on our customers’ behalf, based on the security guarantees of our new ownership validation process. This ensures that customer routes continue to be accepted in every corner of the Internet.

Cloudflare takes the security and stability of the whole Internet very seriously. RPKI is a cryptographically-strong authorization mechanism and is, we believe, substantially more reliable than common practice which relies upon human review of scanned documents. However, deployment and availability of some RPKI-signed artifacts like the AS Path Authorisation (ASPA) object remains limited, and for that reason we are limiting the initial scope of self-serve onboarding to BYOIP prefixes originated from Cloudflare's autonomous system number (ASN) AS 13335. By doing this, we only need to rely on the publication of Route Origin Authorisation (ROA) objects, which are widely available. This approach has the advantage of being safe for the Internet and also meeting the needs of most of our BYOIP customers. 

Today, we take a major step forward in offering customers a more comprehensive IP address management (IPAM) platform. With the recent update to enable multiple services on a single BYOIP prefix and this latest advancement to enable self-serve onboarding via our API, we hope customers feel empowered to take control of their IPs on our network.

We want Cloudflare to feel like an extension of your infrastructure, which is why we originally launched Bring-Your-Own-IP (BYOIP) back in 2020. 

A quick refresher: Bring-your-own-IP is named for exactly what it does - it allows customers to bring their own IP space to Cloudflare. Customers choose BYOIP for a number of reasons, but the main reasons are control and configurability. An IP prefix is a range or block of IP addresses. Routers create a table of reachable prefixes, known as a routing table, to ensure that packets are delivered correctly across the Internet. When a customer's Cloudflare services are configured to use the customer's own addresses, onboarded to Cloudflare as BYOIP, a packet with a corresponding destination address will be routed across the Internet to Cloudflare's global edge network, where it will be received and processed. BYOIP can be used with our Layer 7 services, Spectrum, or Magic Transit. 

Let’s take a step back and take a look at the state of the BYOIP world right now. Let’s say a customer has authority over a range of IP addresses, and they’d like to bring them to Cloudflare. We require customers to provide us with a Letter of Authorization (LOA) and have an Internet Routing Registry (IRR) record matching their prefix and ASN. Once we have this, we require manual review by a Cloudflare engineer. There are a few issues with this process:

• Insecure: The LOA is just a document—a piece of paper. The security of this method rests entirely on the diligence of the engineer reviewing the document. If the review is not able to detect that a document is fraudulent or inaccurate, it is possible for a prefix or ASN to be hijacked.

• Time-consuming: Generating a single LOA is not always sufficient. If you are leasing IP space, we will ask you to provide documentation confirming that relationship as well, so that we can see a clear chain of authorisation from the original assignment or allocation of addresses to you. Getting all the paper documents to verify this chain of ownership, combined with having to wait for manual review can result in weeks of waiting to deploy a prefix!

Moving to a self-serve model allowed us to rethink the manner in which we conduct prefix ownership checks. We asked ourselves: How can we quickly, securely, and automatically prove you are authorized to use your IP prefix and intend to route it through Cloudflare?

We ended up killing two birds with one stone, thanks to our two-step process involving the creation of an RPKI ROA (verification of intent) and modification of IRR or rDNS records (verification of ownership). Self-serve unlocks the ability to not only onboard prefixes more quickly and without human intervention, but also exercises more rigorous ownership checks than a simple scanned document ever could. While not 100% foolproof, it is a significant improvement in the way we verify ownership.

Regional Internet Registries (RIRs) are the organizations responsible for distributing and managing Internet number resources like IP addresses. They are composed of 5 different entities operating in different regions of the world (RIRs). Originally allocated address space from the Internet Assigned Numbers Authority (IANA), they in turn assign and allocate that IP space to Local Internet Registries (LIRs) like ISPs.

This process is based on RIR policies which generally look at things like legal documentation, existing database/registry records, technical contacts, and BGP information. End-users can obtain addresses from an LIR, or in some cases through an RIR directly. As IPv4 addresses have become more scarce, brokerage services have been launched to allow addresses to be leased for fixed periods from their original assignees.

The Internet Routing Registry (IRR) is a separate system that focuses on routing rather than address assignment. Many organisations operate IRR instances and allow routing information to be published, including all five RIRs. While most IRR instances impose few barriers to the publication of routing data, those that are operated by RIRs are capable of linking the ability to publish routing information with the organisations to which the corresponding addresses have been assigned. We believe that being able to modify an IRR record protected in this way provides a good signal that a user has the rights to use a prefix.

Example of a route object containing validation token (using the documentation-only address 192.0.2.0/24):

% whois -h rr.arin.net 192.0.2.0/24

route:          192.0.2.0/24
origin:         AS13335
descr:          Example Company, Inc.
                cf-validation: 9477b6c3-4344-4ceb-85c4-6463e7d2453f
admin-c:        ADMIN2521-ARIN
tech-c:         ADMIN2521-ARIN
tech-c:         CLOUD146-ARIN
mnt-by:         MNT-CLOUD14
created:        2025-07-29T10:52:27Z
last-modified:  2025-07-29T10:52:27Z
source:         ARIN

For those that don’t want to go through the process of IRR-based validation, reverse DNS (rDNS) is provided as another secure method of verification. To manage rDNS for a prefix — whether it's creating a PTR record or a security TXT record — you must be granted permission by the entity that allocated the IP block in the first place (usually your ISP or the RIR).

This permission is demonstrated in one of two ways:

• Directly through the IP owner’s authenticated customer portal (ISP/RIR).

• By the IP owner delegating authority to your third-party DNS provider via an NS record for your reverse zone.

Example of a reverse domain lookup using dig command (using the documentation-only address 192.0.2.0/24):

% dig cf-validation.2.0.192.in-addr.arpa TXT

; <<>> DiG 9.10.6 <<>> cf-validation.2.0.192.in-addr.arpa TXT
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16686
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;cf-validation.2.0.192.in-addr.arpa. IN TXT

;; ANSWER SECTION:
cf-validation.2.0.192.in-addr.arpa. 300 IN TXT "b2f8af96-d32d-4c46-a886-f97d925d7977"

;; Query time: 35 msec
;; SERVER: 127.0.2.2#53(127.0.2.2)
;; WHEN: Fri Oct 24 10:43:52 EDT 2025
;; MSG SIZE  rcvd: 150

So how exactly is one supposed to modify these records? That’s where the validation token comes into play. Once you choose either the IRR or Reverse DNS method, we provide a unique, single-use validation token. You must add this token to the content of the relevant record, either in the IRR or in the DNS. Our system then looks for the presence of the token as evidence that the request is being made by someone with authorization to make the requested modification. If the token is found, verification is complete and your ownership is confirmed!

Ownership is only half the battle; we also need to confirm your intention that you authorize Cloudflare to advertise your prefix. For this, we rely on the gold standard for routing security: the Resource Private Key Infrastructure (RPKI), and in particular Route Origin Authorization (ROA) objects.

A ROA is a cryptographically-signed document that specifies which Autonomous System Number (ASN) is authorized to originate your IP prefix. You can think of a ROA as the digital equivalent of a certified, signed, and notarised contract from the owner of the prefix.

Relying parties can validate the signatures in a ROA using the RPKI.You simply create a ROA that specifies Cloudflare's ASN (AS13335) as an authorized originator and arrange for it to be signed. Many of our customers used hosted RPKI systems available through RIR portals for this. When our systems detect this signed authorization, your routing intention is instantly confirmed. 

Many other companies that support BYOIP require a complex workflow involving creating self-signed certificates and manually modifying RDAP (Registration Data Access Protocol) records—a heavy administrative lift. By embracing a choice of IRR object modification and Reverse DNS TXT records, combined with RPKI, we offer a verification process that is much more familiar and straightforward for existing network operators.

While the new self-serve flow ditches the need for the "dinosaur relic" that is the LOA, many network operators around the world still rely on it as part of the process of accepting prefixes from other networks.

To help ensure your prefix is accepted by adjacent networks globally, Cloudflare automatically generates a document on your behalf to be distributed in place of a LOA. This document provides information about the checks that we have carried out to confirm that we are authorised to originate the customer prefix, and confirms the presence of valid ROAs to authorise our origination of it. In this way we are able to support the workflows of network operators we connect to who rely upon LOAs, without our customers having the burden of generating them.

One concern in designing the Self-Serve API is the trade-off between giving customers flexibility while implementing the necessary safeguards so that an IP prefix is never advertised without a matching service binding. If this were to happen, Cloudflare would be advertising a prefix with no idea on what to do with the traffic when we receive it! We call this “blackholing” traffic. To handle this, we introduced the requirement of a default service binding — i.e. a service binding that spans the entire range of the IP prefix onboarded. 

A customer can later layer different service bindings on top of their default service binding via multiple service bindings, like putting CDN on top of a default Spectrum service binding. This way, a prefix can never be advertised without a service binding and blackhole our customers’ traffic.

Check out our developer docs on the most up-to-date documentation on how to onboard, advertise, and add services to your IP prefixes via our API. Remember that onboardings can be complex, and don’t hesitate to ask questions or reach out to our professional services team if you’d like us to do it for you.

The ability to script and integrate BYOIP management into existing workflows is a game-changer for modern network operations, and we’re only just getting started. In the months ahead, look for self-serve BYOIP in the dashboard, as well as self-serve BYOIP offboarding to give customers even more control.

Cloudflare's self-serve BYOIP API onboarding empowers customers with unprecedented control and flexibility over their IP assets. This move to automate onboarding empowers a stronger security posture, moving away from manually-reviewed PDFs and driving RPKI adoption. By using these API calls, organizations can automate complex network tasks, streamline migrations, and build more resilient and agile network infrastructures.

A BGP zombie is a silly name for a route that has become stuck in the Internet’s Default-Free Zone, aka the DFZ: the collection of all internet routers that do not require a default route, potentially due to a missed or lost prefix withdrawal.

The underlying root cause of a zombie could be multiple things, spanning from buggy software in routers or just general route processing slowness. It’s when a BGP prefix is meant to be gone from the Internet, but for one reason or another it becomes a member of the undead and hangs around for some period of time.

The longer these zombies linger, the more they create operational impact and become a real headache for network operators. Zombies can lead packets astray, either by trapping them inside of route loops or by causing them to take an excessively scenic route. Today, we’d like to celebrate Halloween by covering how BGP zombies form and how we can lessen the likelihood that they wreak havoc on Internet traffic.

To understand the slowness that can often lead to BGP zombies, we need to talk about path hunting. Path hunting occurs when routers running BGP exhaustively search for the best path to a prefix as determined by Longest Prefix Matching (LPM) and BGP routing attributes like path length and local preference. This becomes relevant in our observations of exactly how routes become stuck, for how long they become stuck, and how visible they are on the Internet.

For example, path hunting happens when a more-specific BGP prefix is withdrawn from the global routing table, and networks need to fallback to a less-specific BGP advertisement. In this example, we use 2001:db8::/48 for the more-specific BGP announcement and 2001:db8::/32 for the less-specific prefix. When the /48 is withdrawn by the originating Autonomous System (AS), BGP routers have to recognize that route as missing and begin routing traffic to IPs such as 2001:db8::1 via the 2001:db8::/32 route, which still remains while the prefix 2001:db8::/48 is gone. 

Let’s see what this could look like in action with a few diagrams. 

_{Diagram 1: Active 2001:db8::/48 route}

In this initial state, 2001:db8::/48 is used actively for traffic forwarding, which all flows through AS13335 on the way to AS64511. In this case, AS64511 would be a BYOIP customer of Cloudflare. AS64511 also announces a backup route to another Internet Service Provider (ISP), AS64510, but this route is not active even in AS64510’s routing table for forwarding to 2001:db8::1 because 2001:db8::/48 is a longer prefix match when compared to 2001:db8::/32.

Things get more interesting when AS64510 signals for 2001:db8::/48 to be withdrawn by Cloudflare (AS13335), perhaps because a DDoS attack is over and the customer opts to use Cloudflare only when they are actively under attack.

When the customer signals to Cloudflare (via BGP Control or API call) to withdraw the 2001:db8::/48 announcement, all BGP routers have to converge upon this update, which involves path hunting. AS13335 sends a BGP withdrawal message for 2001:db8::/48 to its directly-connected BGP neighbors. While the news of withdrawal may travel quickly from AS13335 to the other networks, news may travel more quickly to some of the neighbors than others. This means that until everyone has received and processed the withdrawal, networks may try routing through one another to reach the 2001:db8::/48 prefix – even after AS13335 has withdrawn it. 

_{Diagram 2: 2001:db8::/48 route withdrawn via AS13335}

Imagine AS64501 is a little slower than the rest – perhaps due to using older hardware, hardware being overloaded, a software bug, specific configuration settings, poor luck, or some other factor – and still has not processed the withdrawal of the /48. This in itself could be a BGP zombie, since the route is stuck for a small period. Our pings toward 2001:db8::1 are never able to actually reach AS64511, because AS13335 knows the /48 is meant to be withdrawn, but some routers carrying a full table have not yet converged upon that result.

The length of time spent path hunting is amplified by something called the Minimum Route Advertisement Interval (MRAI). The MRAI specifies the minimum amount of time between BGP advertisement messages from a BGP router, meaning it introduces a purposeful number of seconds of delay between each BGP advertisement update. RFC4271 recommends an MRAI value of 30-seconds for eBGP updates, and while this can cut down on the chattiness of BGP, or even potential oscillation of updates, it also makes path hunting take longer. 

At the next cycle of path hunting, even AS64501, which was previously still pointing toward a nonexistent /48 route from AS13335, should find the /32 advertisement is all that is left toward 2001:db8::1. Once it has done so, the traffic flow will become the following: 

_{Diagram 3: Routing fallback to 2001:db8::/32 and 2001:db8::/48 is gone from DFZ}

This would mean BGP path hunting is over, and the Internet has realized that the 2001:db8::/32 is the best route available toward 2001:db8::1, and that 2001:db8::/48 is really gone. While in this example we’ve purposely made path hunting only last two cycles, in reality it can be far more, especially with how highly connected AS13335 is to thousands of peer networks and Tier-1’s globally. 

Now that we’ve discussed BGP path hunting and how it works, you can probably already see how a BGP zombie outbreak can begin and how routing tables can become stuck for a lengthy period of time. Excessive BGP path hunting for a previously-known more-specific prefix can be an early indicator that a zombie could follow.

Zombies have captured our attention more recently as they were noticed by some of our customers leveraging Bring-Your-Own-IP (BYOIP) on-demand advertisement for Magic Transit. BYOIP may be configured in two modes: "always-on", in which a prefix is continuously announced, or "on-demand", where a prefix is announced only when a customer chooses to. For some on-demand customers, announcement and withdrawal cycles may be a more frequent occurrence, which can lead to an increase in BGP zombies.

With that in mind and also knowing how path hunting works, let’s spawn our own zombie onto the Internet. To do so, we’ll take a spare block of IPv4 and IPv6 and announce them like so:

Once the routes are announced and stable, we’ll then proceed to withdraw the more specific routes advertised via Cloudflare globally. With a few quick clicks, we’ve successfully re-animated the dead.

Variant A: Ghoulish Gateways

One place zombies commonly occur is between upstream ISPs. When one router in a given ISP’s network is a little slower to update, routes can become stuck. 

Take, for example, the following loop we observed between two of our upstream partners:

7. be2431.ccr31.sjc04.atlas.cogentco.com
8. tisparkle.sjc04.atlas.cogentco.com
9. 213.144.177.184
10. 213.144.177.184
11. 89.221.32.227
12. (waiting for reply)
13. be2749.rcr71.goa01.atlas.cogentco.com
14. be3219.ccr31.mrs02.atlas.cogentco.com
15. be2066.agr21.mrs02.atlas.cogentco.com
16. telecomitalia.mrs02.atlas.cogentco.com
17. 213.144.177.186
18. 89.221.32.227

Or this loop - observed on the same withdrawal test - between two different providers:

15. if-bundle-12-2.qcore2.pvu-paris.as6453.net
16. if-bundle-56-2.qcore1.fr0-frankfurt.as6453.net
17. if-bundle-15-2.qhar1.fr0-frankfurt.as6453.net
18. 195.219.223.11
19. 213.144.177.186
20. 195.22.196.137
21. 213.144.177.186
22. 195.22.196.137

Variant B: Undead LAN (Local Area Network)

Simultaneously, zombies can occur entirely within a given network. When a route is withdrawn from Cloudflare’s network, each device in our network must individually begin the process of withdrawing the route. While this is generally a smooth process, things can still become stuck.

Take, for instance, a situation where one router inside of our network has not yet fully processed the withdrawal. Connectivity partners will continue routing traffic towards that router (as they have not yet received the withdrawal) while no host remains behind the router which is capable of actually processing the traffic. The result is an internal-only looping path:

10. 192.0.2.112
11. 192.0.2.113
12. 192.0.2.112
13. 192.0.2.113
14. 192.0.2.112
15. 192.0.2.113
16. 192.0.2.112
17. 192.0.2.113
18. 192.0.2.112
19. 192.0.2.113

Unlike most fictionally-depicted hoards of the walking dead, our highly-visible zombie has a limited lifetime in most major networks – in this instance, only around around 6 minutes, after which most had re-converged around the less-specific as the best path. Sadly, this is on the shorter side – in some cases, we have seen long-lived zombies cause reachability issues for more than 10 minutes. It’s safe to say this is longer than most network operators would expect BGP convergence to take in a normal situation. 

But, you may ask – is this the excessive path hunting we talked about earlier, or a BGP zombie? Really, it depends on the expectation and tolerance around how long BGP convergence should take to process the prefix withdrawal. In any case, even over 30 minutes after our withdrawal of our more-specific prefix, we are able to see zombie routes in the route-views public collectors easily:

~ % monocle search --start-ts 2025-10-28T12:40:13Z --end-ts 2025-10-28T13:00:13Z --prefix 198.18.0.0/24
A|1761656125.550447|206.82.105.116|54309|198.18.0.0/24|54309 13335 395747|IGP|206.82.104.31|0|0|54309:111|false|||route-views.ny

You might argue that six to eleven minutes (or more) is a reasonable time for worst-case BGP convergence in the Tier-1 network layer, though that itself seems like a stretch. Even setting that aside, our data shows that very real BGP zombies exist in the global routing table, and they will negatively impact traffic. Curiously, we observed the path hunting delay is worse on IPv4, with the longest observed IPv6 impact in major (Tier-1) networks being just over 4 minutes. One could speculate this is in part due to the much higher number of IPv4 prefixes in the Internet global routing table than the IPv6 global table, and how BGP speakers handle them separately.

_{Source: RIPEstat’s BGPlay}

Part of the delay appears to originate from how interconnected AS13335 is; being heavily peered with a large portion of the Internet increases the likelihood of a route becoming stuck in a given location. Given that, perhaps a zombie would be shorter-lived if we operated in the opposite direction: announcing a less-specific persistently to 13335 and announcing more specifics via our local ISP during normal operation. Since the withdrawal will come from what is likely a less well-peered network, the time-to-convergence may be shorter:

Indeed, as predicted, we still get a stuck route, and it only lives for around 20 seconds in the Tier-1 network layer:

19. be12488.ccr42.ams03.atlas.cogentco.com
20. 38.88.214.142
21. be2020.ccr41.ams03.atlas.cogentco.com
22. 38.88.214.142
23. (waiting for reply)
24. 38.88.214.142
25. (waiting for reply)
26. 38.88.214.142

Unfortunately, that 20 seconds is still an impactful 20 seconds - while better, it’s not where we want to be. The exact length of time will depend on the native ISP networks one is connected with, and it could certainly ease into the minutes worth of stuck routing. 

In both cases, the initial time-to-announce yielded no loss, nor was a zombie created, as both paths remained valid for the entirety of their initial lifetime. Zombies were only created when a more specific prefix was fully withdrawn. A newly-announced route is not subject to path hunting in the same way a withdrawn more-specific route is. As they say, good (new) news travels fast.

Our findings lead us to believe that the withdrawal of a more-specific prefix may lead to zombies running rampant for longer periods of time. Because of this, we are exploring some improvements that make the consequences of BGP zombie routing less impactful for our customers relying on our on-demand BGP functionality.

For the traffic that does reach Cloudflare with stuck routes, we will introduce some BGP traffic forwarding improvements internally that allow for a more graceful withdrawal of traffic, even if routes are erroneously pointing toward us. In many ways, this will closely resemble the BGP well-known no-export community’s functionality from our servers running BGP. This means even if we receive traffic from external parties due to stuck routing, we will still have the opportunity to deliver traffic to our far-end customers over a tunneled connection or via a Cloudflare Network Interconnect (CNI). We look forward to reporting back the positive impact after making this improvement for a more graceful draining of traffic by default. 

For the traffic that does not reach Cloudflare’s edge, and instead loops between network providers, we need to use a different approach. Since we know more-specific to less-specific prefix routing fallback is more prone to BGP zombie outbreak, we are encouraging customers to instead use a multi-step draining process when they want traffic drained from the Cloudflare edge for an on-demand prefix without introducing route loops or blackhole events. The draining process when removing traffic for a BYOIP prefix from Cloudflare should look like this: 

1. The customer is already announcing an example prefix from Cloudflare, ex. 198.18.0.0/24

2. The customer begins natively announcing the prefix 198.18.0.0/24 (i.e. the same-length as the prefix they are advertising via Cloudflare) from their network to the Internet Service Providers that they wish to fail over traffic to.

3. After a few minutes, the customer signals BGP withdrawal from Cloudflare for the 198.18.0.0/24 prefix.

The result is a clean cut over: impactful zombies are avoided because the same-length prefix (198.18.0.0/24) remains in the global routing table. Excessive path hunting is avoided because instead of routers needing to aggressively seek out a missing more-specific prefix match, they can fallback to the same-length announcement that persists in the routing table from the natively-originated path to the customer’s network.

_{Source: RIPEstat’s BGPlay}

We are going to continue to refine our methods of measuring BGP zombies, so you can look forward to more insights in the future. There is also work from others in the community around zombie measurement that is interesting and producing useful data. In terms of combatting the software bugs around BGP zombie creation, routing vendors should implement RFC9687, the BGP SendHoldTimer. The general idea is that a local router can detect via the SendHoldTimer if the far-end router stops processing BGP messages unexpectedly, which lowers the possibility of zombies becoming stuck for long periods of time. 

In addition, it’s worth keeping in mind our observations made in this post about more-specific prefix announcements and excessive path hunting. If as a network operator you rely on more-specific BGP prefix announcements for failover, or for traffic engineering, you need to be aware that routes could become stuck for a longer period of time before full BGP convergence occurs.

If you’re interested in problems like BGP zombies, consider coming to work at Cloudflare or applying for an internship. Together we can help build a better Internet!

Historically, when customers onboarded a BYOIP prefix, they were required to assign it to a single service, binding all IP addresses within that prefix to one service before it was advertised. Once set, the prefix's destination was fixed — to direct traffic exclusively to that service. If a customer wanted to use a different service, they had to onboard a new prefix or go through the cumbersome process of offboarding and re-onboarding the existing one.

As a step towards addressing this limitation, we’ve introduced a new level of flexibility: customers can now use parts of any prefix — whether it’s bound to Cloudflare CDN, Spectrum, or Magic Transit — for additional use with CDN or Spectrum. This enhancement provides much-needed flexibility, enabling businesses to optimize their IP address usage while keeping costs under control. 

Migrating BYOIP prefixes dynamically between Cloudflare services is no trivial task, especially with thousands of servers capable of accepting and processing connections. The problem required overcoming several technical challenges related to IP address management, kernel-level bindings, and orchestration. 

When configuring an IP prefix for a service, we need to update IP address lists and firewall rules on each of our servers to allow only the traffic we expect for that service, such as opening ports 80 and 443 to allow HTTP and HTTPS traffic for the Cloudflare CDN. We use Linux iptables and IP sets for this.

Migrating IP prefixes to a different service involves dynamically reassigning them to different IP sets and iptable rules. This requires automated updates across a large-scale distributed environment.

As prefixes shift between services, it is critical that servers update their IP sets and iptable rules dynamically to ensure traffic is correctly routed. Failure to do so could lead to routing loops or dropped connections.  

Most web applications bind to a list of IP addresses at startup, and listen on only those IPs until shutdown. To allow customers to change the IPs bound to each service dynamically, we needed a way to add and remove IPs from a running service, without restarting it. Tubular is a BPF program we wrote that runs on Cloudflare servers that allows services to listen on a single socket, dynamically updating the list of addresses that are routed to that socket over the lifetime of the service, without requiring it to restart when those addresses change.

A significant engineering challenge was extending Tubular to support traffic destined for Cloudflare’s CDN.  Without this enhancement, customers would be unable to leverage dynamic reassignment to bind prefixes onboarded through Spectrum to the Cloudflare CDN, limiting flexibility across services.

Cloudflare’s CDN depends on each server running an NGINX ingress proxy to terminate incoming connections. Due to the scale and performance limitations of NGINX, we are actively working to replace it by 2026. In the interim, however, we still depend on the current ingress proxy to reliably handle incoming connections.

One limitation is that this ingress proxy does not support systemd socket activation, a mechanism Tubular relies on to integrate with other Cloudflare services on each server. For services that do support systemd socket activation, systemd independently starts the sockets for the owning service and passes them to Tubular, allowing Tubular to easily detect and route traffic to the correct terminating service.

Since this integration model is not feasible, an alternative solution was required. This was addressed by introducing a shared Unix domain socket between Tubular and the ingress proxy service on each server. Through this channel,  the ingress proxy service explicitly transmits socket information to Tubular, enabling it to correctly register the sockets in its datapath.

The final challenge was deploying the Tubular-ingress proxy integration across the fleet of servers without disrupting active connections. As of April 2025, Cloudflare handles an average of 71 million HTTP requests per second, peaking at 100 million. To safely deploy at this scale, the necessary Tubular and ingress proxy configuration changes were staged across all Cloudflare servers without disrupting existing connections. The final step involved adding bindings — IP addresses and ports corresponding to Cloudflare CDN prefixes — to the Tubular configuration. These bindings direct connections through Tubular via the Unix sockets registered during the previous integration step. To minimize risk, bindings were gradually enabled in a controlled rollout across the global fleet.

This high-level representation of the Tubular data plane binds together the Layer 4 protocol (TCP), prefix (192.0.2.0/24 - which is 254 usable IP addresses), and port number 0 (any port). When incoming packets match this combination, they are directed to the correct socket of the service — in this case, Spectrum.​

In the following example, TCP 192.0.2.200/32 has been upgraded to the Cloudflare CDN via the edge Service Bindings API. Tubular dynamically consumes this information, adding a new entry to its data plane bindings and socket table. Using Longest Prefix Match, all packets within the 192.0.2.0/24 range port 0 will be routed to Spectrum, except for 192.0.2.200/32 port 443, which will be directed to the Cloudflare CDN.

Our goal is to achieve a quick transition of IP address prefixes between services when initiated by customers, which requires a high level of coordination. We need to ensure that changes propagate correctly across all servers to maintain stability. Currently, when a customer migrates a prefix between services, there is a 4-6 hour window of uncertainty where incoming packets may be dropped due to a lack of guaranteed routing. To address this, we are actively implementing systems that will reduce this transition time from hours to just a matter of minutes, significantly improving reliability and minimizing disruptions.

Service Bindings are mappings that control whether traffic destined for a given IP address is routed to Magic Transit, the CDN pipeline, or the Spectrum pipeline.

Consider the example in the diagram below. One of our customers, a global finance infrastructure platform, is using BYOIP and has a /24 range bound to Spectrum for DDoS protection of their TCP and UDP traffic. However, they are only using a few addresses in that range for their Spectrum applications, while the rest go unused. In addition, the customer is using Cloudflare’s CDN for their Layer 7 traffic and wants to set up Static IPs, so that their customers can allowlist a consistent set of IP addresses owned and controlled by their own network infrastructure team. Instead of using up another block of address space, they asked us whether they could carve out those unused sub-ranges of the /24 prefix.

From there, we set out to determine how to selectively map sub-ranges of the onboarded prefix to different services using service bindings:

• 192.0.2.0/24 is already bound to Spectrum

  • 192.0.2.0/25 is updated and bound to CDN

  • 192.0.2.200/32 is also updated bound to CDN

Both the /25 and /32 are sub-ranges within the /24 prefix and will receive traffic directed to the CDN. All remaining IP addresses within the /24 prefix, unless explicitly bound, will continue to use the default Spectrum service binding.

As you can see in this example, this approach provides customers with greater control and agility over how their IP address space is allocated. Instead of rigidly assigning an entire prefix to a single service, users can now tailor their IP address usage to match specific workloads or deployment needs. Setting this up is straightforward — all it takes is a few HTTP requests to the Cloudflare API. You can define service bindings by specifying which IP addresses or subnets should be routed to CDN, Spectrum, or Magic Transit. This allows you to tailor traffic routing to match your architecture without needing to restructure your entire IP address allocation. The process remains consistent whether you're configuring a single IP address or splitting up larger subnets, making it easy to apply across different parts of your network. The foundational technical work addressing the underlying architectural challenges outlined above made it possible to streamline what could have been a complex setup into a straightforward series of API interactions.

We envision a future where customers have granular control over how their traffic moves through Cloudflare’s global network, not just by service, but down to the port level. A single prefix could simultaneously power web applications on CDN, protect infrastructure through Magic Transit, and much more. This isn't just flexible routing, but programmable traffic orchestration across different services. What was once rigid and static becomes dynamic and fully programmable to meet each customer’s unique needs. 

If you are an existing BYOIP customer using Magic Transit, CDN, or Spectrum, check out our configuration guide here. If you are interested in bringing your own IP address space and using multiple Cloudflare services on it, please reach out to your account team to enable setting up this configuration via API or reach out to sales@cloudflare.com if you’re new to Cloudflare.

We’re pleased to introduce Advanced DDoS Alerts. Advanced DDoS Alerts are customizable and provide users the flexibility they need when managing many Internet properties. Users can easily define which alerts they want to receive — for which DDoS attack sizes, protocols and for which Internet properties.

This release includes two types of Advanced DDoS Alerts:

1. Advanced HTTP DDoS Attack Alerts - Available to WAF/CDN customers on the Enterprise plan, who have also subscribed to the Advanced DDoS Protection service.

2. Advanced L3/4 DDoS Attack Alerts - Available to Magic Transit and Spectrum BYOIP customers on the Enterprise plan.

Standard DDoS Alerts are available to customers on all plans, including the Free plan. Advanced DDoS Alerts are part of Cloudflare’s Advanced DDoS service.

Distributed Denial of Service attacks are cyber attacks that aim to take down your Internet properties and make them unavailable for your users. As early as 2017, Cloudflare pioneered the Unmetered DDoS Protection to provide all customers with DDoS protection, without limits, to ensure that their Internet properties remain available. We’re able to provide this level of commitment to our customers thanks to our automated DDoS protection systems. But if the systems operate automatically, why even be alerted?

Well, to put it plainly, when our DDoS protection systems kick in, they insert ephemeral rules inline to mitigate the attack. Many of our customers operate business critical applications and services. When our systems make a decision to insert a rule, customers might want to be able to verify that all the malicious traffic is mitigated, and that legitimate user traffic is not. Our DDoS alerts begin firing as soon as our systems make a mitigation decision. Therefore, by informing our customers about a decision to insert a rule in real time, they can observe and verify that their Internet properties are both protected and available.

The standard DDoS Alerts alert you on DDoS attacks that target any and all of your Cloudflare-protected Internet properties. However, some of our customers may manage large numbers of Internet properties ranging from hundreds to hundreds of thousands. The standard DDoS Alerts would notify users every time one of those properties would come under attack — which could become very noisy.

The Advanced DDoS Alerts address this concern by allowing users to select the specific Internet properties that they want to be notified about; zones and hostnames for WAF/CDN customers, and IP prefixes for Magic Transit and Spectrum BYOIP customers.

Creating an Advanced HTTP DDoS Attack Alert: selecting zones and hostnames

Creating an Advanced L3/4 DDoS Attack Alert: selecting prefixes

The standard DDoS Alerts alert you on DDoS attacks of any size. Well, almost any size. We implemented minimal alert thresholds to avoid spamming our customers’ email inboxes. Those limits are very small and not customer-configurable. As we’ve seen in the recent DDoS trends report, most of the attacks are very small — another reason why the standard DDoS Alert could become noisy for customers that only care about very large attacks. On the opposite end of the spectrum, choosing not to alert may become too quiet for customers that do want to be notified about smaller attacks.

The Advanced DDoS Alerts let customers choose their own alert threshold. WAF/CDN customers can define the minimum request-per-second rate of an HTTP DDoS attack alert. Magic Transit and Spectrum BYOIP customers can define the packet-per-second and Megabit-per-second rates of a L3/4 DDoS attack alert.

Creating an Advanced HTTP DDoS Attack Alert: defining request rate

Creating an Advanced L3/4 DDoS Attack Alert: defining packet/bit rate

As part of the Advanced L3/4 DDoS Alerts, we also let our users define the protocols to be alerted on. If a Magic Transit customer manages mostly UDP applications, they may not care if TCP-based DDoS attacks target it. Similarly, if a Spectrum BYOIP customer only cares about HTTP/TCP traffic, other-protocol-based attacks could be of no concern to them.

Creating an Advanced L3/4 DDoS Attack Alert: selecting the protocols

We’ll show here how to create an Advanced HTTP DDoS Alert, but the process to create a L3/4 alert is similar. You can view a more detailed guide on our developers website.

First, click here or log in to your Cloudflare account, navigate to Notifications and click Add. Then select the Advanced HTTP DDoS Attack Alert or Advanced L3/4 DDoS Attack Alert (based on your eligibility). Give your alert a name, an optional description, add your preferred delivery method (e.g., Webhook) and click Next.

Step 1: Creating an Advanced HTTP DDoS Attack Alert

Second, select the domains you’d like to be alerted on. You can also narrow it down to specific hostnames. Define the minimum request-per-second rate to be alerted on, click Save, and voilà.

Step 2: Defining the Advanced HTTP DDoS Attack Alert conditions

Cloudflare Advanced DDoS Alerts aim to provide our customers with configurable controls to make better decisions for their own environments. Customers can now be alerted on attacks based on which domain/prefix is being attacked, the size of the attack, and the protocol of the attack. We recognize that the power to configure and control DDoS attack alerts should ultimately be left up to our customers, and we are excited to announce the availability of this functionality.

Want to learn more about Advanced DDoS Alerts? Visit our developer site.

Interested in upgrading to get Advanced DDoS Alerts? Contact your account team.

New to Cloudflare? Speak to a Cloudflare expert.

This past April, we announced the Cloudflare for SaaS Beta which makes our SSL for SaaS product available to everyone. This allows any customer — from first-time developers to large enterprises — to use Cloudflare for SaaS to extend our full product suite to their own customers. SSL for SaaS is the subset of Cloudflare for SaaS features that focus on a customer’s Public Key Infrastructure (PKI) needs.

Today, we’re excited to announce all the customizations that our team has been working on for our Enterprise customers — for both Cloudflare for SaaS and SSL for SaaS.

If you’re running a SaaS company, your solution might exist as a subdomain of your SaaS website, e.g. template.<mysaas>.com, but ideally, your solution would allow the customer to use their own vanity hostname for it, such as example.com.

The most common way to begin using a SaaS company’s service is to point a CNAME DNS record to the subdomain that the SaaS provider has created for your application. This ensures traffic gets to the right place, and it allows the SaaS provider to make infrastructure changes without involving your end customers.

We kept this in mind when we built our SSL for SaaS a few years ago. SSL for SaaS takes away the burden of certificate issuance and management from the SaaS provider by proxying traffic through Cloudflare’s edge. All the SaaS provider needs to do is onboard their zone to Cloudflare and ask their end customers to create a CNAME to the SaaS zone — something they were already doing.

The big benefit of giving your customers a CNAME record (instead of a fixed IP address) is that it gives you, the SaaS provider, more flexibility and control. It allows you to seamlessly change the IP address of your server in the background. For example, if your IP gets blocked by ISP providers, you can update that address on your customers’ behalf with a CNAME record. With a fixed A record, you rely on each of your customers to make a change.

While the CNAME record works great for most customers, some came back and wanted to bypass the limitation that CNAME records present. RFC 1912 states that CNAME records cannot coexist with other DNS records, so in most cases, you cannot have a CNAME at the root of your domain, e.g. example.com. Instead, the CNAME needs to exist at the subdomain level, i.e. www.example.com. Some DNS providers (including Cloudflare) bypass this restriction through a method called CNAME flattening.

Since SaaS providers have no control over the DNS provider that their customers are using, the feedback they got from their customers was that they wanted to use the apex of their zone and not the subdomain. So when our SaaS customers came back asking us for a solution, we delivered. We call it Apex Proxying.

For our SaaS customers who want to allow their customers to proxy their apex to their zone, regardless of which DNS provider they are using, we give them the option of Apex Proxying. Apex Proxying is an SSL for SaaS feature that gives SaaS providers a pair of IP addresses to provide to their customers when CNAME records do not work for them.

Cloudflare starts by allocating a dedicated set of IPs for the SaaS provider. The SaaS provider then gives their customers these IPs that they can add as A or AAAA DNS records, allowing them to proxy traffic directly from the apex of their zone.

While this works for most, some of our customers want more flexibility. They want to have multiple IPs that they can change, or they want to assign different sets of customers to different buckets of IPs. For those customers, we give them the option to bring their own IP range, so they control the IP allocation for their application.

Last year, we announced Bring Your Own IP (BYOIP), which allows customers to bring their own IP range for Cloudflare to announce at our edge. One of the benefits of BYOIP is that it allows SaaS customers to allocate that range to their account and then, instead of having a few IPs that their customers can point to, they can distribute all the IPs in their range.

SaaS customers often require granular control of how their IPs are allocated to different zones that belong to different customers. With 256 IPs to use, you have the flexibility to either group customers together or to give them dedicated IPs. It’s up to you!

While we’re on the topic of grouping customers, let’s talk about how you might want to do this when sending traffic to your origin.

When setting up Cloudflare for SaaS, you indicate your fallback origin, which defines the origin that all of your Custom Hostnames are routed to. This origin can be defined by an IP address or point to a load balancer defined in the zone. However, you might not want to route all customers to the same origin. Instead, you want to route different customers (or custom hostnames) to different origins — either because you want to group customers together or to help you scale the origins supporting your application.

Our Enterprise customers can now choose a custom origin that is not the default fallback origin for any of their Custom Hostnames. Traditionally, this has been done by emailing your account manager and requesting custom logic at Cloudflare's edge, a very cumbersome and outdated practice. But now, customers can easily indicate this in the UI or in their API requests.

Oftentimes, SaaS providers have customers that don’t just want their domain to stay protected and encrypted, but also the subdomains that fall under it.

We wanted to give our Enterprise customers the flexibility to extend this benefit to their end customers by offering wildcard support for Custom Hostnames.

Wildcard Custom Hostnames extend the Custom Hostname’s configuration from a specific hostname — e.g. “blog.example.com” — to the next level of subdomains of that hostname, e.g. “*.blog.example.com”.

To create a Custom Hostname with a wildcard, you can either indicate Enable wildcard support when creating a Custom Hostname in the Cloudflare dashboard or when you’re creating a Custom Hostname through the API, indicate wildcard: “true”.

Now let’s switch gears to TLS certificate management and the improvements our team has been working on.

SSL for SaaS was built to reduce the burden of certificate management for SaaS providers. The initial functionality was meant to serve most customers and their need to issue, maintain, and renew certificates on their customers’ behalf. But one size does not fit all, and some of our customers have more specific needs for their certificate management — and we want to make sure we accommodate them.

One of the superpowers of SSL for SaaS is that it allows Cloudflare to manage all the certificate issuance and renewals on behalf of our customers and their customers. However, some customers want to allow their end customers to upload their own certificates.

For example, a bank may only trust certain certificate authorities (CAs) for their certificate issuance. Alternatively, the SaaS provider may have initially built out TLS support for their customers and now their customers expect that functionality to be available. Regardless of the reasoning, we have given our customers a few options that satisfy these requirements.

For customers who want to maintain control over their TLS private keys or give their customers the flexibility to use their certification authority (CA) of choice, we allow the SaaS provider to upload their customer’s certificate.

If you are a SaaS provider and one of your customers does not allow third parties to generate keys on their behalf, then you want to allow that customer to upload their own certificate. Cloudflare allows SaaS providers to upload their customers’ certificates to any of their custom hostnames — in just one API call!

Some SaaS providers never want a person to see private key material, but want to be able to use the CA of their choice. They can do so by generating a Certificate Signing Request (CSR) for their Custom Hostnames, and then either use those CSRs themselves to order certificates for their customers or relay the CSRs to their customers so that they can provision their own certificates. In either case, the SaaS provider is able to then upload the certificate for the Custom Hostname after the certificate has been issued from their customer’s CA for use at Cloudflare’s edge.

For our customers who need to customize their configuration to handle specific rules for their customer’s domains, they can do so by using Custom Metadata and Workers.

By adding metadata to an individual custom hostname and then deploying a Worker to read the data, you can use the Worker to customize per-hostname behavior.

Some customers use this functionality to add a customer_id field to each custom hostname that they then send in a request header to their origin. Another way to use this is to set headers like HTTP Strict Transport Security (HSTS) on a per-customer basis.

Tomorrow, we have a very special announcement about how you can now get more visibility into your customers’ traffic and — more importantly —  how you can share this information back to them.

If you’re an Enterprise customer, and you’re interested in any of these features, reach out to your account team to get access today!