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We operate a network where we have 'tons' of VM servers that are physically hosted on many many blade chassis. The thought behind the original design was to simply put them in one very large broadcast domain so there are no restrictions on where you move blades or VMs to. Need more IPs? Just allocate a new block and keep adding blades.

As we own our own IP space this lead to allocating a

  • /22
  • /20
  • /24
  • /24

All on one L2 segment. I understand this is against 'conventional' IT wisdom but besides the potential for a loop is this really "that bad" on modern network equipment? These VM servers are essentially just plugged into one of two switches that are daisy chained together.

Most of the traffic is unicast and besides ARP there isn't a lot of broadcast traffic. All the servers are connected w\ 10G links so a few Mbps of ARP seems to be nothing. We push around 60 Gbps of BW.

With that being said my network equipment consists of:

  • Juniper MX204 routers.
  • Cisco N9K-C93180YC-EX switches
  • Servers are standard HP Moonshots.

We tightly control the network so the potential for a misconfig taking down the entire stack is small. Do you think this could be causing performance issues or in the grand scheme of things is nothing?

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin ♦
    Dec 17, 2020 at 21:12

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Can modern network equipment handle very large broadcast domains?

Your switches won't have any problem, but that's not why you should be concerned. Broadcasts affect hosts, since the host CPU has to examine every broadcast packet to see if it's important. Also, vSwitches aren't as efficient as dedicated hardware.

Traffic between subnets has to flow in and out of the same router interface. That potentially is a bottleneck.

The lack of VLANs will also increase your security vulnerabilities

Do you think this could be causing performance issues?

Probably not, but I'm more concerned that you have to ask that question, since it tells me you're not monitoring your network very well.

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  • Most of the traffic is DIA so there's no inter-subnet traffic. As far as the hosts are concerned do you think that a modern linux server with a modern Xenon CPU (don't know exact specs), and like 48 GB or RAM. To be fair it's only a few Mbps of ARP. I havn't seen any issues yet with those vSwitches on the blade chassis.
    – n1nja09-2w3r
    Sep 11, 2020 at 14:36
  • I'm not really a server guy. You might ask about this on Server Fault.
    – Ron Trunk
    Sep 11, 2020 at 14:50

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