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Thursday, March 31, 2011

How to connect the wireless bridge to a layer 2 port

QSolved Question: We have a Microwave wireless bridge connecting two 3750 switches. The wireless bridge is connected to a layer 3 port on the 3750 at each end and all is working fine today. We have some application requirements that we need to connect the wireless bridge to a layer 2 port, basically a trunk port on the 3750 at each end. Please see attached diagram.Has anyone done this before ?

Qsolved Answer : I've seen this done before where the wireless bridge simply acts as a transport mechanism. If you have a stable microwave link, there's no real issues but obviously this type of set up is more susceptible to interference issues.

Example: Figure 4 outdoor wireless VLANs deployment with Cisco equipment.Click here for the reference link.

Points of interest

- Be aware of any limitations with MTU for your microwave link and ensure it can accomodate any extra bytes if you are using 802.1q trunking

18bytes for ethernet header inc CRC

4 byte for the 802.1q tag

1500bytes for the IP MTU

total = 1522bytes.

Brain storming a little

- unstable trunk links will affect switches that carry the same VLANS as the trunk link - typical Layer 2 spanning-tree type issues

- if you intend to use a redundant links, you'll need to consider the fact that if the wireless goes down, the links on the switch will stay up, potentially black holing traffic, where as Layer 3 routing protocols have hello packets which could detect if the link is down.

You could use probes and scripts such as EEM to automate these kinds of things.

Citation - This blog post does not reflect original content from the author. Rather it summarizes content that are relevant to the topic from different sources in the web. The sources might include any online discussion boards, forums, websites and others.

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