# BYOIP

## What Is BYOIP?

BYOIP (Bring Your Own IP) lets you take an IPv4 prefix you already own and put it to work on Zenlayer. You tell the platform three things — the CIDR, which ISP line should carry it, and the origin ASN that should announce it — and Zenlayer turns that prefix into an Elastic IP pool you can allocate addresses from.

From the runtime side, nothing about those addresses is special. They behave like any other EIP: bind to an instance, add to a NAT Gateway SNAT entry, release when you're done. What is different is *ownership* — customer CIDRs carry a flag that tells your own address space apart from Zenlayer-assigned address space at a glance.

![BYOIP Architecture](/files/bxOztAagORguS0frSMW0)

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## When to Use BYOIP

**You need to keep addresses that partners already trust.** Allow-lists, firewall rules, outbound DNS records, sender reputation scores, and compliance inventories often accumulate around specific IPs over years. BYOIP lets you move the workload to Zenlayer without asking every downstream system to re-approve a fresh address.

![Preserve existing IP allow-lists by bringing your own CIDR](/files/IM9DFxEtXO7Pd0qvHbGq)

**You want a stable egress identity from your own address space.** Once EIPs are allocated from the customer pool, they can be referenced by NAT Gateway SNAT entries the same way any other EIP can. Traffic from hundreds of private instances then exits the internet on *your* prefix.

![Use a BYOIP EIP as the NAT Gateway SNAT source](/files/xAXRkv470le5CKe8VzmP)

**You need a specific origin ASN on the public route.** The origin ASN is part of the create and update flow, so the AS-path that the rest of the internet sees ends at the ASN you chose — as long as RPKI authorizes that ASN to originate the prefix.

![BYOIP announced under your origin ASN, gated by RPKI](/files/BYPoRKWwY97njOwOl4D6)

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## What BYOIP Is Not

* **Not an IPv6 onboarding flow.** The customer-CIDR flow is IPv4 only.
* **Not a generic pool-management product.** You don't create or name the EIP pool — the platform creates one when the CIDR is accepted and returns its pool ID.
* **Not a path for private or unregistered ASNs.** The origin ASN must pass platform validation; private ASN ranges are rejected.
* **Not a bypass for normal EIP rules.** Once an address is allocated, region, binding, and release rules match the rest of EIP.

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## In This Guide

| Page                                                                                                 | What You'll Learn                                                               |
| ---------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------- |
| [Customer CIDR](/welcome/elastic-compute/networking/01-overview-4/02-customer-cidr.md)               | The customer CIDR resource — attributes, states, and how it maps to an EIP pool |
| [Origin ASN and RPKI](/welcome/elastic-compute/networking/01-overview-4/03-origin-asn.md)            | How origin ASN selection and RPKI validation gate the announcement              |
| [EIP Allocation](/welcome/elastic-compute/networking/01-overview-4/04-eip-allocation.md)             | Pulling EIPs from the customer pool and using them like any other EIP           |
| [Onboarding Lifecycle](/welcome/elastic-compute/networking/01-overview-4/05-onboarding-lifecycle.md) | End-to-end: prepare the ROA, create the CIDR, allocate, bind, retire            |
| [Best Practices](/welcome/elastic-compute/networking/01-overview-4/06-best-practices.md)             | Recommendations and troubleshooting                                             |
| [Configuration Guide](/welcome/elastic-compute/networking/01-overview-4/07-configuration-guide.md)   | Step-by-step console instructions                                               |

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## Limits

| Resource                | Limit |
| ----------------------- | ----- |
| BYOIP prefixes per team | 10    |

***

## Frequently Asked Questions

**What prefix size should I bring?** Bring an IPv4 prefix that is routable on the public internet. In practice, prefixes more specific than `/24` are commonly filtered, so `/24` is the usual lower bound.

**Does Zenlayer check RPKI?** Yes. Both the initial create and any origin-ASN update call RPKI validation before the route is accepted.

**Can I change the ASN later?** Yes, as long as the new ASN is on the platform's supported list and RPKI authorizes it for the prefix. Publish the new ROA first, then submit the update.

**Can these EIPs be used with NAT Gateway?** Yes. Once allocated, they are regular EIPs and can appear in SNAT entries the same way as Zenlayer-assigned EIPs.

**Does the customer CIDR keep a separate identifier?** No. The CIDR itself is the identifier. You refer to it by the prefix you brought in, not by a synthetic ID.


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