> For the complete documentation index, see [llms.txt](https://docs.console.zenlayer.com/welcome/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.console.zenlayer.com/welcome/ip-transit/high-availability.md).

# IP Transit High Availability (HA)

IP Transit High Availability (HA) allows you to build a redundant egress architecture using two co-located physical ports, eliminating single points of failure and ensuring business continuity. The dual-link HA architecture delivers an SLA of **99.95%**, higher than the single-link standard.

{% hint style="info" %} <mark style="color:blue;">**Note**</mark>

<mark style="color:blue;">HA instances are currently only supported on automated (BR) devices. Upgrading existing single-link instances to HA is not supported in this release.</mark>
{% endhint %}

## Operating Modes

HA instances support two operating modes, which can be switched at any time after creation:

| Mode               | Alias          | Description                                                                                                                                                                                          |
| ------------------ | -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Active-Standby** | Primary-Backup | The primary port carries all traffic. If the primary port fails, traffic automatically switches to the standby port within seconds. Suitable for workloads that require deterministic routing paths. |
| **Active-Active**  | Load Balancing | Both links forward traffic simultaneously using ECMP. Maximizes bandwidth utilization; traffic migrates smoothly if one link fails.                                                                  |

## Routing Mode

HA instances support **Static Routing** only.

## Prerequisites

* Your account has completed identity verification and has sufficient balance.
* The target city has **two or more** available IP Transit physical ports with status **UP**.
* VLAN IDs are planned for both the primary and standby ports (the same value is recommended for both).
* You have determined the required bandwidth specification and billing model (Flat Rate / Burstable 95th).