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Is there any downside in broadcasting multiple wireless networks from the same router?

Is there an upper limit?

EDIT: I am mainly concerned with signal interference. I might be misunderstanding. Can different networks broadcast by the same router have different channels/frequencies? I am just having trouble seeing how the router is able to accommodate that with the same antenna.

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    Your question isn't clear. Please elaborate the scenario and what you're trying to do. – Zac67 Feb 19 '18 at 22:13
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    Please explain what you mean. Many companies have multiple SSIDs on a WAP that uses VLAN back to a switch, possible back to a WLC. A router in the network could be configured to route between the networks. – Ron Maupin Feb 19 '18 at 22:17
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Is there any downside in broadcasting multiple wireless networks from the same router?

If you mean from the same radio on an AP/router, then absolutely. Each additional SSID requires a certain amount of overhead, at the very least in the form of beacon frames and other management traffic. This reduces the efficiency of the wireless network and reduces performance with the effects increasing for each additional SSID.

Most of the references citing statistics for multiple SSIDs of which I am aware of are older documentation. The numbers may not be as exact due to changes in 802.11, but the principles still apply. Data rates have increased, but so has the size of the typical beacon frame. Anyhow, here are references from Arubu's Airheads Community and Revolution Wi-Fi that provide statistics showing the impact of multiple SSIDs.

Is there an upper limit?

Different hardware/software may have limits that are imposed, but there is no limit as defined by the standards. However there are maximum recommended limits and the general rule of thumb is to use the fewest SSIDs as possible.

Cisco's best practices document recommends 1-3 SSIDs:

It is recommended to have one to three SSIDs for an enterprise, and one SSID for high-density designs.

Aruba's best practices give an even lower target at 2:

Use as few SSIDs as possible. Generally, one WPA2 Enterprise SSID and one Open SSID are more than enough.

Can different networks broadcast by the same router have different channels/frequencies?

Only if the SSIDs are using two different radios. If the different SSIDs are using the same radio, then no, they must use the same channel/frequency.

Note: Portions of this post are copied from my own response to a similar question on ServerFault.

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  • I think your data is old. For 11b, SSIDs make a big difference, but at 11n or 11ac speeds, it's not significant. – Ron Trunk Feb 23 '18 at 22:29
  • @RonTrunk, as I mention, the data is dated. However the principles still hold. While the data rates have significantly increased, so has the amount of information transmitted in beacon frames and probe responses. As those are management traffic, they also typically go at the lowest supported base data rate. This still makes them a factor today and why all major wireless vendors still recommend as a best practice that you minimize your SSIDs or deploy no more than 4 (highest number I am familiar with from any best practice document). – YLearn Feb 23 '18 at 23:01
  • I guess we'll have to agree to disagree. But as it turns out, the OP was asking a different question. – Ron Trunk Feb 24 '18 at 0:03
  • @RonTrunk, while 802.11ac is faster than 802.11a, without tuning of the data rates the beacon data rate is still 6Mbps. This means the older percentage of airtime used by beacons in 802.11a/b/g still applies today (and is likely worse due to more information elements contained in the beacons). Just because clients can make better use of the airtime unused by management traffic doesn't make the inefficiency of airtime use by multiple SSIDs any better. – YLearn Feb 24 '18 at 4:31
  • OK Fine. IF you have a poorly designed, untuned wireless network, and IF you're running at the lowest speeds possible, then yes, you shouldn't have more than one or two SSIDs. But then I'm sure your network has other problems. OTOH, if you've taken the time to design a modern, reliable wireless infrastructure (you know, the kind I'm sure you actually do), then you can add all the SSIDs you want without noticeably affecting performance. – Ron Trunk Feb 24 '18 at 16:43
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Your question isn't quiet clear but I believe you are referring to the number of SSID.

Is there an upper limit?

Yes,The number of SSID depends upon the Wireless chipset you use in the router.Generally,Chipset vendors like Quantenna/Broadcom will have minimum capacity to configure 4 SSIDs(Two 2.4 ghz Generic SSIDs and Two 5Ghz Guest SSIDs) .It can go higher also.AFAIK,I have seen maximum of 6 SSIDs in the data model.

In some cases,Even if the firmware supports 16 SSIDs but the software might have only configured 4 SSIDs. If your router support Open Wrt then you can find the command to list the number of SSIDs supported by your firmware.

In short,The number of SSIDs are clearly depended upon the Wireless chipset you use in the Router.Perhaps,you can find that information in the respective datasheet of the same.

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Essentially, no. There may be system limitations as Maverick has pointed out very well, but apart from that there is no clear downside for using multiple SSIDs on the same access point(s) if you want to separate the traffic or zones.

Edit after YLearn's comment: I'm aware that SSID broadcasting and such is done at the lowest speed but was assuming you were asking about just a very few SSIDs in parallel (like 2-4 or so). However, that wasn't clear and my answer above might be misleading. Each SSID costs air time and thus reduces the effective throughput. Basically, you have to be careful when adding more than a (very) few SSIDs.

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  • I typically appreciate and agree with many of the answers provided by Zac67, but on this one I just have to disagree as there clearly are downsides for using multiple SSIDs on the same access point back by multiple sources and why the major wireless vendors recommend using as few SSIDs as possible. – YLearn Feb 22 '18 at 7:02
  • I'll check out your answer, seems there's something to learn - thx! – Zac67 Feb 22 '18 at 7:17
  • That's the beauty of the field....there is always something new to learn, even if you are an expert on the topic. If you don't keep learning you only make yourself obsolete. – YLearn Feb 22 '18 at 7:36
  • I appreciate and agree with almost all the answers by @YLearn, but not this one. What you say is certainly true in the days of 802.11b, but 11n or 11ac makes the overhead trivial. Beacon frames from 3 APs on one channel with 5 SSIDs take up about 4% of the airtime at 24 Mbps. – Ron Trunk Feb 23 '18 at 22:21
  • @RonTrunk, yes, the impact is less. However while the data rates have significantly increased, so has the amount of information transmitted in beacon frames and probe responses. As those are management traffic, they also typically go at the lowest supported base data rate. This still makes them a factor today and why all major wireless vendors still recommend as a best practice that you minimize your SSIDs or deploy no more than 4 (highest number I am familiar with from any best practice document). – YLearn Feb 23 '18 at 23:00
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Wireless routers (actually, they're called access points) can only transmit and receive on one channel at a time. So no, they don't transmit on different channels. Dual band access points (2.4 and 5 GHz) have two radios and two antennas so they can operate on both bands simultaneously.

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