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title: Switches Common
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## Terms

| Cisco IOS | Brocade ICX |
| :--- | :--- |
| Access port \(VLAN\) | Untagged port |
| Trunk port \(VLAN\) | Tagged port |
| Native VLAN | Dual mode |

## Spanning Tree

### Variants

| Names | Supporting Devices\* | Description |
| :--- | :--- | :--- |
| 802.1D, STP | Cisco IOS, Linksys LGS | Single instance, slow |
| PVST/PVST+ | Cisco IOS | Like STP, one instance per VLAN |
| VSTP | Juniper | Compatible with Cisco's PVST |
| 802.1w, RSTP | Brocade ICX, Linksys LGS | Single instance, fast, backwards-compatible with STP. |
| Rapid-PVST+ | Cisco IOS | Like PVST+ but based on RSTP |
| VSTP | Juniper | Based on RSTP, compatible with STP and Cisco's PVST |
| 802.1s, MSTP, MST | Cisco IOS | Multiple instances with configurable VLAN members |
| 802.1Q |  | ??? |

\(\*\) Very incomplete list.

### Notes

- Use extended system ID for multi-VLAN switches.
- Make sure all switches are using compatible variants and default priorities.
- Make sure all VLANs are running STP or that STP is running globally \(not per VLAN\).
- STP \(excluding per-VLAN STP and generally not MST\) \(including rapid versions\) will consider multiple links between switches a loop, even when the links carry different VLANs.
- The bridge priority should generally be a multiple of 4096.
- PVST and 802.1Q regions cannot interoperate directly, but can through PVST+ regions.

#### Cisco IOS

- Disable VTP, it's dangerous if not used properly. It also doesn't carry MST configuration.
- Rapid-PVST+ ignores UplinkFast and BackboneFast and supports UDLD.

### Compatibility Between Switch Models

#### Alternative 1

- Cisco IOS \(Cat 3750G\): `rapid-pvst`
- Brocade \(ICX 6610\): `802.1w`
- Linksys \(LGS326\): `stp` \(slow but works\)
- Use the same default priority, e.g. 32768.

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