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| 4.1 |  | Methods of Inter-VLAN Routing |
| 4.1.6 |  | Router-on-a-stick |

The technique of implementing Inter-VLAN routing using a single, trunk-connected, Fast Ethernet link to a router is known by a number of common names. These include “Router-on-a-stick”, “Lollipop routing” and “One armed bandit".

The primary advantage of using a trunk link is a reduction in router and switch ports. Not only can this save money, it can also reduce configuration complexity. Consequently, the trunk-connected router approach can scale to a much larger number of VLANs than a one-link-per-VLAN design.

However, the trunk-connected router configuration has disadvantages, including the following:

- There is a possibility of inadequate bandwidth for each VLAN.
- Additional overhead on the router can occur.
- Older versions of the Cisco IOS Software support only a limited set of features on trunked interfaces and may support only Cisco’s proprietary Inter-Switch Link (ISL) trunking encapsulation.
- Trunking is not supported on most Cisco routers with standard Ethernet interfaces and some lower-end routers with Fast Ethernet interfaces.

With regard to inadequate bandwidth for each VLAN, consider the situation where all VLANs must share the Fast Ethernet 100 Mbps of bandwidth. A single VLAN could easily consume the entire capacity of the router or the link, especially in the event of a broadcast storm or spanning tree problem. Furthermore, the up-and-back nature of router-on-a-stick designs effectively doubles the bandwidth consumption of the link.

With regard to the additional overhead on the router caused by using a trunk-connected router, not only must the router perform normal routing and data-forwarding duties, it must also handle the additional encapsulation used by the trunking protocol.