Many sites across many countries and we have assigned a /16 to each country. We have matched the 2nd Octet to (or as close as we can to the Country’s International Dialling Code), e.g
10.44.0.0 /16 – UK (+44 is the UK Dialling Code)
10.49.0.0 /16 – Germany (+49 is the German Dialling Code)
10.7.0.0 /16 – Russia (+7 is the Russian Dialling Code)
Some of our sites/countries have 3 digit dialling codes, e.g Oman is +968). We use the first two numbers in these cases.
e.g 10.96.0.0 /16
This has worked well for us.
At a lower level, where we have multiple sites in a country we then assign a subset of the /16 to each site,
UK site 1 – 10.44.0.0 /17
UK Site 2 – 10.44.128.0 /20
UK Site 3 – 10.44.144.0 /20
At site level we have then assigned a mix /24s /25s and so forth for Management, Data, Voice, Servers, Storage, Printers etc. This is where you would need to tailor things your own needs.
We also try and keep the vlan names and numbers consistent across all our sites to keep everything to a standard.