%PDF-1.4 %âãÏÓ 1 0 obj << /Type /Catalog /Pages 2 0 R >> endobj 2 0 obj << /Type /Pages /Count 2 /Kids [5 0 R 7 0 R] >> endobj 3 0 obj << /Type /Font /Subtype /Type1 /BaseFont /Helvetica >> endobj 4 0 obj << /Type /Font /Subtype /Type1 /BaseFont /Helvetica-Bold >> endobj 5 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 595.28 841.89] /Resources << /Font << /F1 3 0 R /F2 4 0 R >> >> /Contents 6 0 R >> endobj 6 0 obj << /Length 5562 >> stream BT /F2 21 Tf 0.06 0.08 0.12 rg 1 0 0 1 46 789.89 Tm (My VMs stopped talking to each other after I messed) Tj ET BT /F2 21 Tf 0.06 0.08 0.12 rg 1 0 0 1 46 763.89 Tm (with the virtual switch settings, Is this the application) Tj ET BT /F2 21 Tf 0.06 0.08 0.12 rg 1 0 0 1 46 737.89 Tm (virtual switch causing it?) Tj ET BT /F2 11 Tf 0.72 0.14 0.18 rg 1 0 0 1 46 701.89 Tm (TechRounder Help Center PDF) Tj ET BT /F1 9.5 Tf 0.36 0.39 0.46 rg 1 0 0 1 46 685.89 Tm (Live article:) Tj ET BT /F1 9.5 Tf 0.36 0.39 0.46 rg 1 0 0 1 46 673.39 Tm (https://www.techrounder.com/help/my-vms-stopped-talking-to-each-other-after-i-messed-with-the-virtual-switch-set) Tj ET BT /F1 9.5 Tf 0.36 0.39 0.46 rg 1 0 0 1 46 660.89 Tm (tings-is-this-the-application-virtual-switch-causing-it/) Tj ET q 0.82 0.85 0.9 RG 1 w 46 642.39 m 549.28 642.39 l S Q BT /F1 10 Tf 0.24 0.27 0.32 rg 1 0 0 1 46 630.39 Tm (By Vipin PG | Published August 14, 2026 | Updated August 14, 2026 | Topic: Solution | 3 min read) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 609.39 Tm (Short answer: no, it's almost certainly not an "application virtual switch." That term belongs to Cisco's) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 594.39 Tm (ACI gear - it's a specific branded component for their datacenter fabric, not anything you'll find in) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 579.39 Tm (Hyper-V Manager, VMware Workstation, ESXi, or Proxmox. If you're running a home lab or a local) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 564.39 Tm (hypervisor and your VMs suddenly can't see each other, what you touched was a regular virtual) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 549.39 Tm (switch, and the fix is usually a 10-minute config check, not a reinstall.) Tj ET BT /F1 10.5 Tf 0.28 0.31 0.36 rg 1 0 0 1 56 525.39 Tm (Quote: If you don't manage Cisco ACI hardware at work, forget the "application" part entirely. Just think) Tj ET BT /F1 10.5 Tf 0.28 0.31 0.36 rg 1 0 0 1 56 511.39 Tm (of it as "the virtual switch settings," and work through the list below in order.) Tj ET BT /F2 13 Tf 0.08 0.1 0.14 rg 1 0 0 1 46 485.39 Tm (Check the switch type first) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 463.39 Tm (This is the number one cause, and it's an easy one to trip over without realizing it. Hyper-V has three) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 448.39 Tm (switch types, and each behaves completely differently:) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 426.39 Tm (- External - bound to a physical NIC, lets VMs talk to each other, the host, and the outside network) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 409.59 Tm (- Internal - VMs can talk to each other and to the host, but not to the outside world) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 392.79 Tm (- Private - VMs can only talk to each other. Not even the host can see this traffic) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 375.99 Tm (If you were "messing with the virtual switch" and accidentally changed the type - say, from External) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 360.99 Tm (to Private, or created a brand new switch instead of editing the existing one - every VM attached to it) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 345.99 Tm (loses whatever connectivity that type doesn't support. Open Hyper-V Manager -> Virtual Switch) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 330.99 Tm (Manager and confirm the type is actually what you think it is.) Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 306.99 Tm (Get-VMSwitch | Format-Table Name, SwitchType) Tj ET BT /F2 13 Tf 0.08 0.1 0.14 rg 1 0 0 1 46 282.49 Tm (VLAN ID mismatch \(the sneaky one\)) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 260.49 Tm (This trips up more people than switch type does, mainly because it's invisible unless you go looking) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 245.49 Tm (for it. If you enabled "Enable virtual LAN identification" on the switch or on an individual VM's) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 230.49 Tm (network adapter - even by accident, even just clicking through a settings dialog - that VM now only) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 215.49 Tm (talks to other devices tagged with the exact same VLAN ID. Two VMs on the identical switch but) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 200.49 Tm (different VLAN IDs simply won't see each other's traffic at all. No error, no warning, just silence.) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 178.49 Tm (Check each VM's adapter settings individually:) Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 154.49 Tm (Get-VMNetworkAdapterVlan -VMName "VM1") Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 137.615 Tm (Get-VMNetworkAdapterVlan -VMName "VM2") Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 119.115 Tm (If they don't match \(or one has tagging enabled and the other doesn't\), that's your problem. To reset a) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 104.115 Tm (VM back to untagged:) Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 80.115 Tm (Set-VMNetworkAdapterVlan -VMName "VM1" -Untagged) Tj ET q 0.86 0.88 0.92 RG 1 w 46 42 m 549.28 42 l S Q BT /F1 8.4 Tf 0.42 0.45 0.5 rg 1 0 0 1 46 30 Tm (TechRounder Help Center | Page 1 of 2) Tj ET BT /F1 7.2 Tf 0.42 0.45 0.5 rg 1 0 0 1 46 19 Tm (https://www.techrounder.com/pdf/help/my-vms-stopped-talking-to-each-other-after-i-messed-with-the-virtual-switch-settings-is-this-the-application-virtu) Tj ET BT /F1 7.2 Tf 0.42 0.45 0.5 rg 1 0 0 1 46 11.2 Tm (al-switch-causing-it.pdf) Tj ET endstream endobj 7 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 595.28 841.89] /Resources << /Font << /F1 3 0 R /F2 4 0 R >> >> /Contents 8 0 R >> endobj 8 0 obj << /Length 4265 >> stream BT /F2 13 Tf 0.08 0.1 0.14 rg 1 0 0 1 46 789.89 Tm (Confirm both VMs are actually on the same switch) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 767.89 Tm (Sounds obvious, but if you were reconfiguring things, it's easy to reattach one VM to a newly created) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 752.89 Tm (switch while the other stays on the old one. They'll look connected in Device Manager inside the guest) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 737.89 Tm (OS, but they're on two separate isolated networks that never touch.) Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 713.89 Tm (Get-VMNetworkAdapter -VMName "VM1" | Select VMName, SwitchName) Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 697.015 Tm (Get-VMNetworkAdapter -VMName "VM2" | Select VMName, SwitchName) Tj ET BT /F2 13 Tf 0.08 0.1 0.14 rg 1 0 0 1 46 672.515 Tm (Windows Firewall on the VMs is blocking ICMP) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 650.515 Tm (If ping is your test and everything above checks out, the guest OS firewall is next. By default, Windows) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 635.515 Tm (blocks inbound ICMPv4 echo requests unless you've enabled "File and Printer Sharing" or added a) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 620.515 Tm (specific rule. This one bites people constantly because it has nothing to do with the switch at all - it just) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 605.515 Tm (happens to surface at the same time you're troubleshooting switch settings.) Tj ET BT /F1 9.5 Tf 0.18 0.2 0.24 rg 1 0 0 1 54 581.515 Tm (New-NetFirewallRule -DisplayName "Allow ICMPv4" -Protocol ICMPv4 -IcmpType 8 -Enabled True -Action Allow) Tj ET BT /F2 13 Tf 0.08 0.1 0.14 rg 1 0 0 1 46 557.015 Tm (The switch got corrupted after a host reboot) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 535.015 Tm (Less common, but worth knowing: some Hyper-V hosts develop a genuinely corrupted virtual switch) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 520.015 Tm (port after a Windows Update reboot. Symptoms are odd - internet works, but internal traffic between) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 505.015 Tm (VMs \(or specific apps like AD replication or file shares\) silently breaks. If nothing else on this list) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 490.015 Tm (fixes it, the workaround is to move the VMs off the switch, delete and recreate the switch port, then) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 475.015 Tm (reattach them.) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 453.015 Tm (1. Note the switch name and settings in Virtual Switch Manager before touching anything) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 436.215 Tm (2. Move all affected VMs to a temporary switch \(or disconnect their adapters\)) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 419.415 Tm (3. Delete the problematic virtual switch) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 402.615 Tm (4. Recreate it with the same name and settings) Tj ET BT /F1 10.5 Tf 0.2 0.23 0.28 rg 1 0 0 1 46 385.815 Tm (5. Reattach the VMs and test connectivity again) Tj ET BT /F2 13 Tf 0.08 0.1 0.14 rg 1 0 0 1 46 363.015 Tm (If you're on VMware instead of Hyper-V) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 341.015 Tm (Same troubleshooting order applies, just different menus: check the vSwitch's port group VLAN ID,) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 326.015 Tm (confirm both VMs are on the same port group \(not just the same vSwitch - port groups matter\), and) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 311.015 Tm (check the guest firewall the same way. The "External/Internal/Private" concept maps loosely to) Tj ET BT /F1 11 Tf 0.14 0.16 0.2 rg 1 0 0 1 46 296.015 Tm (whether the vSwitch has an uplink adapter attached at all.) Tj ET q 0.86 0.88 0.92 RG 1 w 46 42 m 549.28 42 l S Q BT /F1 8.4 Tf 0.42 0.45 0.5 rg 1 0 0 1 46 30 Tm (TechRounder Help Center | Page 2 of 2) Tj ET BT /F1 7.2 Tf 0.42 0.45 0.5 rg 1 0 0 1 46 19 Tm (https://www.techrounder.com/pdf/help/my-vms-stopped-talking-to-each-other-after-i-messed-with-the-virtual-switch-settings-is-this-the-application-virtu) Tj ET BT /F1 7.2 Tf 0.42 0.45 0.5 rg 1 0 0 1 46 11.2 Tm (al-switch-causing-it.pdf) Tj ET endstream endobj xref 0 9 0000000000 65535 f 0000000015 00000 n 0000000064 00000 n 0000000127 00000 n 0000000197 00000 n 0000000272 00000 n 0000000414 00000 n 0000006027 00000 n 0000006169 00000 n trailer << /Size 9 /Root 1 0 R >> startxref 10485 %%EOF