diff --git a/app/components/form/fields/TextField.tsx b/app/components/form/fields/TextField.tsx
index e6c21798a..e341be08a 100644
--- a/app/components/form/fields/TextField.tsx
+++ b/app/components/form/fields/TextField.tsx
@@ -56,6 +56,8 @@ export interface TextFieldProps<
   units?: string
   validate?: Validate<FieldPathValue<TFieldValues, TName>, TFieldValues>
   control: Control<TFieldValues>
+  /** Alters the value of the input during the field's onChange event. */
+  transform?: (value: string) => FieldPathValue<TFieldValues, TName>
 }
 
 export function TextField<
@@ -119,6 +121,7 @@ export const TextFieldInner = <
   tooltipText,
   required,
   id: idProp,
+  transform,
   ...props
 }: TextFieldProps<TFieldValues, TName> & UITextAreaProps) => {
   const generatedId = useId()
@@ -144,6 +147,10 @@ export const TextFieldInner = <
               // for the calling code despite the actual input value necessarily
               // being a string.
               onChange={(e) => {
+                if (transform) {
+                  onChange(transform(e.target.value))
+                  return
+                }
                 if (type === 'number') {
                   if (e.target.value.trim() === '') {
                     onChange(0)
diff --git a/app/forms/network-interface-create.tsx b/app/forms/network-interface-create.tsx
index edec5d565..a459c9aa8 100644
--- a/app/forms/network-interface-create.tsx
+++ b/app/forms/network-interface-create.tsx
@@ -80,7 +80,12 @@ export default function CreateNetworkInterfaceForm({
         required
         control={form.control}
       />
-      <TextField name="ip" label="IP Address" control={form.control} />
+      <TextField
+        name="ip"
+        label="IP Address"
+        control={form.control}
+        transform={(ip) => (ip.trim() === '' ? undefined : ip)}
+      />
     </SideModalForm>
   )
 }
diff --git a/app/test/e2e/network-interface-create.e2e.ts b/app/test/e2e/network-interface-create.e2e.ts
new file mode 100644
index 000000000..21c01ae93
--- /dev/null
+++ b/app/test/e2e/network-interface-create.e2e.ts
@@ -0,0 +1,78 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * Copyright Oxide Computer Company
+ */
+import { test } from '@playwright/test'
+
+import { expect, expectRowVisible } from './utils'
+
+test('can create a NIC with a specified IP address', async ({ page }) => {
+  // go to an instance’s Network Interfaces page
+  await page.goto('/projects/mock-project/instances/db1/network-interfaces')
+
+  // stop the instance
+  await page.getByRole('button', { name: 'Instance actions' }).click()
+  await page.getByRole('menuitem', { name: 'Stop' }).click()
+
+  // open the add network interface side modal
+  await page.getByRole('button', { name: 'Add network interface' }).click()
+
+  // fill out the form
+  await page.getByLabel('Name').fill('nic-1')
+  await page.getByRole('button', { name: 'VPC' }).click()
+  await page.getByRole('option', { name: 'mock-vpc' }).click()
+  await page.getByRole('button', { name: 'Subnet' }).click()
+  await page.getByRole('option', { name: 'mock-subnet' }).click()
+  await page.getByLabel('IP Address').fill('1.2.3.4')
+
+  const sidebar = page.getByRole('dialog', { name: 'Add network interface' })
+
+  // test that the form can be submitted and a new network interface is created
+  await sidebar.getByRole('button', { name: 'Add network interface' }).click()
+  await expect(sidebar).toBeHidden()
+
+  await expectRowVisible(page.getByRole('table'), { name: 'nic-1', ip: '1.2.3.4' })
+})
+
+test('can create a NIC with a blank IP address', async ({ page }) => {
+  // go to an instance’s Network Interfaces page
+  await page.goto('/projects/mock-project/instances/db1/network-interfaces')
+
+  // stop the instance
+  await page.getByRole('button', { name: 'Instance actions' }).click()
+  await page.getByRole('menuitem', { name: 'Stop' }).click()
+
+  // open the add network interface side modal
+  await page.getByRole('button', { name: 'Add network interface' }).click()
+
+  // fill out the form
+  await page.getByLabel('Name').fill('nic-2')
+  await page.getByRole('button', { name: 'VPC' }).click()
+  await page.getByRole('option', { name: 'mock-vpc' }).click()
+  await page.getByRole('button', { name: 'Subnet' }).click()
+  await page.getByRole('option', { name: 'mock-subnet' }).click()
+
+  // make sure the IP address field has a non-conforming bit of text in it
+  await page.getByLabel('IP Address').fill('x')
+
+  // try to submit it
+  const sidebar = page.getByRole('dialog', { name: 'Add network interface' })
+  await sidebar.getByRole('button', { name: 'Add network interface' }).click()
+
+  // it should error out
+  // todo: improve error message from API
+  await expect(sidebar.getByText('Unknown server error')).toBeVisible()
+
+  // make sure the IP address field has spaces in it
+  await page.getByLabel('IP Address').fill('    ')
+
+  // test that the form can be submitted and a new network interface is created
+  await sidebar.getByRole('button', { name: 'Add network interface' }).click()
+  await expect(sidebar).toBeHidden()
+
+  // ip address is auto-assigned
+  await expectRowVisible(page.getByRole('table'), { name: 'nic-2', ip: '123.45.68.8' })
+})