I split my network(s) into subnets (sharing the same wire, not to be confused with the actual subnets which don't share the same wire) which correspond to routability policies. This in turn involves firewall rules, routing table entries, and DHCP configs corresponding to those subnets.

I give away the software which does the following. I get this (and a lot more) for every host on my network, and I know what every host is.

    # peers upstairs-roku.m3047 +addr +serv
    dns.google [8.8.4.4]                                              domain [53]     
    dns.google [8.8.8.8]                                              domain [53]     
    athena.m3047 [10.0.0.220]                                         domain [53]     
    mediaservices.cdn-apple.com [23.46.228.133]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.134]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.135]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.137]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.138]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.139]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.140]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.142]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.143]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.144]                       https [443]     
    mediaservices.cdn-apple.com [23.46.228.145]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.169]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.176]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.178]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.185]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.186]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.187]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.188]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.193]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.196]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.201]                       https [443]     
    mediaservices.cdn-apple.com [23.213.34.203]                       https [443]     
    nrdp.push.prod.netflix.com [35.81.198.46]                         www [80]        
    ec2-35-86-100-253.us-west-2.compute.amazonaws.com [35.86.100.253] psbserver [2350]
    austin.logs.roku.com [35.212.27.142]                              https [443]     
    scribe.logs.roku.com [35.212.34.174]                              https [443]     
    austin.logs.roku.com [35.212.72.105]                              https [443]     
    austin.logs.roku.com [35.212.119.44]                              https [443]     
    display.ravm.tv [35.212.178.254]                                  https [443]     
    logs.netflix.com [44.226.179.188]                                 https [443]     
    logs.netflix.com [44.228.67.58]                                   https [443]     
    nrdp.push.prod.netflix.com [44.229.50.4]                          www [80]        
    logs.netflix.com [44.229.122.169]                                 https [443]     
    nrdp.push.prod.netflix.com [44.232.75.216]                        www [80]        
    api.roku.com [44.249.213.211]                                     https [443]     
    nrdp.prod.ftl.netflix.com [45.57.40.1]                            https [443]     
    nrdp.prod.ftl.netflix.com [45.57.41.1]                            https [443]     
    nrdp.push.prod.netflix.com [52.24.26.117]                         www [80]        
    logs.netflix.com [52.33.247.19]                                   https [443]     
    themes-service.sr.roku.com [54.200.214.141]                       https [443]     
    occ-0-1009-1007.1.nflxso.net [198.38.112.135]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.144]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.145]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.165]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.169]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.170]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.172]                     www [80]        
    occ-0-1009-1007.1.nflxso.net [198.38.112.178]                     www [80]        
    mdns.mcast.net [224.0.0.251]                                      mdns [5353]     
    239.255.255.250 [239.255.255.250]                                 ssdp [1900]