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Joachim Wiberg
c3d17586fd
Fix #1506: restore the VLAN interface documentation that was lost when networking.md was split into per-topic pages. Content adapted from the v25.11.0 networking.md VLAN section, plus a new "Stacked (Q-in-Q)" section showing `eth0.10.20`-style nesting and the layered `show interface` rendering of the parent chain. Update the interface-type table in networking.md to point at the new vlan.md instead of the dangling ethernet.md#vlan-interfaces anchor. ChangeLog: document the user-facing changes on this branch (YANG model upgrade, layered show interface output, auto-negotation typo fix) and the new VLAN documentation. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
90 lines
3.3 KiB
Markdown
90 lines
3.3 KiB
Markdown
# VLAN Interfaces
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A VLAN interface is an interface stacked on top of another Linux interface
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that filters traffic for a single 802.1Q VID. `tcpdump` on a VLAN interface
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shows only frames matching that VID, compared to *all* VIDs when listening
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on the lower-layer interface.
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This page covers VLAN interfaces stacked on Ethernet, on a VLAN-filtering
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bridge, and on other VLAN interfaces. For VLAN handling *inside* a bridge
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(port VIDs, tagged/untagged membership, pvid), see [VLAN Filtering
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Bridge](bridging.md#vlan-filtering-bridge).
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## On Top of an Ethernet Interface
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A VLAN interface for VID 20 on top of an Ethernet interface `eth0` is by
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convention named `eth0.20`.
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<pre class="cli"><code>admin@example:/> <b>configure</b>
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admin@example:/config/> <b>edit interface eth0.20</b>
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admin@example:/config/interface/eth0.20/> <b>show</b>
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type vlan;
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vlan {
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tag-type c-vlan;
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id 20;
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lower-layer-if eth0;
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}
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admin@example:/config/interface/eth0.20/> <b>leave</b>
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</code></pre>
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The `tag-type` defaults to `c-vlan` (802.1Q customer VLAN, EtherType 0x8100).
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Set to `s-vlan` (802.1ad service VLAN, EtherType 0x88A8) to terminate an outer
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S-Tag.
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> [!TIP]
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> If you name your VLAN interface `foo0.N` or `vlanN`, where `N` is a
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> number, the CLI infers the interface type automatically. Otherwise
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> the type must be set explicitly.
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## On Top of a Bridge
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When the lower-layer interface is a VLAN-filtering bridge, the VLAN interface
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gives the CPU an IP-addressable endpoint inside the bridged broadcast domain
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for that VID. This pattern is named `vlanN` by convention.
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<pre class="cli"><code>admin@example:/> <b>configure</b>
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admin@example:/config/> <b>edit interface vlan10</b>
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admin@example:/config/interface/vlan10/> <b>set vlan id 10</b>
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admin@example:/config/interface/vlan10/> <b>set vlan lower-layer-if br0</b>
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admin@example:/config/interface/vlan10/> <b>leave</b>
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</code></pre>
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The bridge `br0` must have VLAN 10 configured with the bridge itself as a
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tagged member. See [VLAN Filtering Bridge](bridging.md#vlan-filtering-bridge)
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for the bridge-side configuration.
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## Stacked (Q-in-Q)
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VLAN interfaces can be stacked. A VLAN interface whose lower-layer is itself
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a VLAN interface terminates the inner tag, leaving the outer tag for the
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parent to handle.
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<pre class="cli"><code>admin@example:/> <b>configure</b>
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admin@example:/config/> <b>edit interface eth0.10</b>
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admin@example:/config/interface/eth0.10/> <b>set vlan tag-type s-vlan</b>
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admin@example:/config/interface/eth0.10/> <b>leave</b>
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admin@example:/config/> <b>edit interface eth0.10.20</b>
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admin@example:/config/interface/eth0.10.20/> <b>show</b>
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type vlan;
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vlan {
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tag-type c-vlan;
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id 20;
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lower-layer-if eth0.10;
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}
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admin@example:/config/interface/eth0.10.20/> <b>leave</b>
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</code></pre>
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The summary view shows each VLAN row pointing at its immediate parent:
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<pre class="cli"><code>admin@example:/> <b>show interface</b>
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<span class="header">INTERFACE PROTOCOL STATE DATA </span>
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eth0.10 vlan UP vid: 10
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│ ipv4 10.0.10.1/24 (static)
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└ eth0
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eth0.10.20 vlan UP vid: 20
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│ ipv4 10.0.10.20/28 (static)
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└ eth0.10
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</code></pre>
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