This document describes how to modify VLAN attachments and Border Gateway
Protocol (BGP) sessions for Cross-Cloud Interconnect.

> [!NOTE]
> **Note:** For definitions of terms used on this page, see [Cloud Interconnect key terms](https://docs.cloud.google.com/network-connectivity/docs/interconnect/concepts/terminology).

The following table describes properties of VLAN attachments and their BGP
sessions, along with information about how to modify them.

| Property | How to modify |
|---|---|
| Description Capacity MTU | For details, see the next section [Modifying description, capacity, and MTU](https://docs.cloud.google.com/network-connectivity/docs/interconnect/how-to/cci/modifying-vlan-attachments#modify-description-capacity-mtu). Modifications are immediate and in rare cases, can cause traffic disruption. If traffic is disrupted, the disruption lasts less than a minute. |
| Whether a VLAN attachment is enabled or disabled | To disable or re-enable a VLAN attachment, see [Disable VLAN attachments](https://docs.cloud.google.com/network-connectivity/docs/interconnect/how-to/cci/disabling-vlans). |
| VLAN ID BGP IP addresses (Cloud Router IP address, remote cloud router IP address) | You can't modify these properties for existing attachments. Instead, you must re-create the VLAN attachment. |
| MD5 authentication | Update the BGP session by following the steps in [Add authentication to an existing session](https://docs.cloud.google.com/network-connectivity/docs/router/how-to/use-md5-authentication#add-authentication). |
| Peer ASN | Update the BGP session by using the following resources: - [View BGP session configuration](https://docs.cloud.google.com/network-connectivity/docs/router/how-to/viewing-router-details#bgp-configuration) - The [`glcoud compute routers update-bgp-peer` command reference](https://docs.cloud.google.com/sdk/gcloud/reference/compute/routers/update-bgp-peer) - The [`routers.update` API method reference](https://docs.cloud.google.com/compute/docs/reference/rest/v1/routers/update) |

## Modify description, capacity, and MTU

The section provides instructions for updating the description, capacity,
and maximum transmission unit (MTU) of a VLAN attachment. Changing the
attributes of a VLAN attachment, in rare cases, can cause traffic disruption.
If traffic is disrupted, the disruption typically lasts less than a minute.

To make use of the 1500-byte MTU, the VPC network that uses
the attachment must have an [MTU](https://docs.cloud.google.com/vpc/docs/mtu) set to `1500`.
In addition, the remote cloud resources must have an MTU set to`1500`.
If your network has the default MTU of `1460`, leave the field at `1440`.

### Console

1. In the Google Cloud console, go to the Cloud Interconnect
   **VLAN attachments** tab.

   [Go to VLAN attachments](https://console.cloud.google.com/hybrid/interconnects/list?tab=attachments)
2. Select the VLAN attachment to modify.

3. On the attachment's detail page, click **Edit**.

4. Modify your VLAN attachment:

   - **Description**: Information about the VLAN attachment.
   - **Capacity**: The maximum bandwidth of the attachment.
   - **Maximum transmission unit (MTU)**: The MTU of the attachment.
5. Click **Save**.

### gcloud

Use the
[`gcloud compute interconnects attachments dedicated update` command](https://docs.cloud.google.com/sdk/gcloud/reference/compute/interconnects/attachments/dedicated/update):

```
gcloud compute interconnects attachments dedicated update NAME \
    --region=REGION \
    --description=DESCRIPTION \
    --bandwidth=BANDWIDTH \
    --mtu MTU
```

Replace the following:

- `NAME`: the name of the VLAN attachment
- `REGION`: the region of the attachment
- `DESCRIPTION`: a description of the attachment
- `BANDWIDTH`: the provisioned capacity of the attachment
- `MTU`: the MTU of the attachment

## What's next

- To learn more about Cross-Cloud Interconnect, see the
  [Cross-Cloud Interconnect overview](https://docs.cloud.google.com/network-connectivity/docs/interconnect/concepts/cci-overview).

- To help you solve common issues that you might encounter when using
  Cloud Interconnect, see
  [Troubleshooting](https://docs.cloud.google.com/network-connectivity/docs/interconnect/support/troubleshooting#cci).