no ip subnet-zero command

Add to the above, old Cisco routers (before IOS version 12.0). Defaulted to disallow subnet zero. So if there is such a router in your network, you might run into trouble if other routers are using subnet zero. The trivial solution is to enable subnet zero on that old router, but if you can't do that for some administrative/organizational/permissions reasons, then you might need to use no ip subnet-zero on the other routers just to cope with the old router.

A better solution would be to pay for better routers and get the address space. I mean when your talking about pre v12 your talking about some old ass routers hardly production models.

A better solution would be to pay for better routers and get the address space. I mean when your talking about pre v12 your talking about some old ass routers hardly production models.

Indeed pre 12.0 router are very old. I'm working for more than 10 years with Cisco devices and as far as I remember I've never had to work with release pre 12.0(7)T...

I think nowadays the use of subnet-zero is not an issue anymore, that why Cisco allows its use by default.

A better solution would be to pay for better routers and get the address space. I mean when your talking about pre v12 your talking about some old ass routers hardly production models.

Yup, I agree, I've never seen it in production, so I guess no ip subnet-zero is practically useless.

However, I noticed that some CCNA/CCNP Cisco students/learners buy those routers (say the 2500 series) because of their relatively cheap prices. Specially CCNP takers who usually need at least 4 routers, it can be expensive buying all of those as say 2600 or 3600 series. So they'd buy one or two and the rest are old.

No I understand how it works... I just want to know why you would ever want to do that? What is the point of making hosts 1-62 and 191-254 not usable? It just seems like a waste.

lets say the fuckers on subnet-zero r playing a little too much on the internet while they should be working....

you could make an access-list orrr

no ip subnet-zero!

IP subnet zero has but one use today IMO. Catching out the unwary on exam sims! Cisco like to throw in the occasional lab or routing question with the rider "IP subnet zero is not configured" to make the candidate think.
In a production network, it's a non issue as already mentioned. IP Subnet Zero is on by default and usable.