diff --git a/mock-api/msw/db.ts b/mock-api/msw/db.ts
index 0c1533f91..c6a08f619 100644
--- a/mock-api/msw/db.ts
+++ b/mock-api/msw/db.ts
@@ -68,14 +68,15 @@ export const resolvePoolSelector = (
     | { pool: string; type: 'explicit' }
     | { type: 'auto'; ip_version?: IpVersion | null }
     | undefined,
-  poolType?: IpPoolType
+  poolType: IpPoolType,
+  siloId: string = defaultSilo.id
 ) => {
   if (poolSelector?.type === 'explicit') {
     return lookup.ipPool({ pool: poolSelector.pool })
   }
 
   // For 'auto' type, find the default pool for the specified IP version and pool type
-  const silo = lookup.silo({ silo: defaultSilo.id })
+  const silo = lookup.silo({ silo: siloId })
   const links = db.ipPoolSilos.filter((ips) => ips.silo_id === silo.id && ips.is_default)
 
   // Filter candidate pools by both IP version and pool type
@@ -83,8 +84,7 @@ export const resolvePoolSelector = (
     const pool = db.ipPools.find((p) => p.id === ips.ip_pool_id)
     if (!pool) return false
 
-    // If poolType specified, filter by it
-    if (poolType && pool.pool_type !== poolType) return false
+    if (pool.pool_type !== poolType) return false
 
     // If IP version specified, filter by it
     if (poolSelector?.ip_version && pool.ip_version !== poolSelector.ip_version) {
@@ -106,9 +106,8 @@ export const resolvePoolSelector = (
 
   const link = candidateLinks[0]
   if (!link) {
-    const typeStr = poolType ? ` ${poolType}` : ''
     const versionStr = poolSelector?.ip_version ? ` ${poolSelector.ip_version}` : ''
-    throw notFoundErr(`default${typeStr}${versionStr} pool for silo '${defaultSilo.id}'`)
+    throw notFoundErr(`default ${poolType}${versionStr} pool for silo '${siloId}'`)
   }
   return lookupById(db.ipPools, link.ip_pool_id)
 }
diff --git a/mock-api/msw/handlers.ts b/mock-api/msw/handlers.ts
index cbda97ede..ac172e71e 100644
--- a/mock-api/msw/handlers.ts
+++ b/mock-api/msw/handlers.ts
@@ -395,10 +395,10 @@ export const handlers = makeHandlers({
           return true // For mock purposes, just use first unicast pool
         })
       })
-      pool = poolWithIp || resolvePoolSelector(undefined, 'unicast')
+      pool = poolWithIp || resolvePoolSelector(undefined, 'unicast', project.silo_id)
     } else {
       // type === 'auto'
-      pool = resolvePoolSelector(addressAllocator.pool_selector, 'unicast')
+      pool = resolvePoolSelector(addressAllocator.pool_selector, 'unicast', project.silo_id)
       ip = getIpFromPool(pool)
     }
 
@@ -640,7 +640,7 @@ export const handlers = makeHandlers({
         // which aren't quite as good as checking that there are actually IPs
         // available, but they are good things to check
         // Ephemeral IPs must use unicast pools
-        const pool = resolvePoolSelector(ip.pool_selector, 'unicast')
+        const pool = resolvePoolSelector(ip.pool_selector, 'unicast', project.silo_id)
         getIpFromPool(pool)
 
         // Validate that external IP version matches NIC's IP stack
@@ -773,7 +773,7 @@ export const handlers = makeHandlers({
         floatingIp.instance_id = instanceId
       } else if (ip.type === 'ephemeral') {
         // Ephemeral IPs must use unicast pools
-        const pool = resolvePoolSelector(ip.pool_selector, 'unicast')
+        const pool = resolvePoolSelector(ip.pool_selector, 'unicast', project.silo_id)
         const firstAvailableAddress = getIpFromPool(pool)
 
         db.ephemeralIps.push({
@@ -959,8 +959,9 @@ export const handlers = makeHandlers({
   },
   instanceEphemeralIpAttach({ path, query: projectParams, body }) {
     const instance = lookup.instance({ ...path, ...projectParams })
+    const instanceProject = lookup.project(projectParams)
     // Ephemeral IPs must use unicast pools
-    const pool = resolvePoolSelector(body.pool_selector, 'unicast')
+    const pool = resolvePoolSelector(body.pool_selector, 'unicast', instanceProject.silo_id)
     const ip = getIpFromPool(pool)
 
     // Validate that external IP version matches primary NIC's IP stack