Any reason to avoid /16 in 2017?



  • Hi everyone, I was just thinking about merging two /24 subnet that are like X.X.0.0 and X.X.120.0 (running out of IPs)… some apps that run on that contains weird static-ip configuration (like SAP B1 services with hardcoded IP, CCTV ecc), so I cannot easily reconfigure everything from scratch with DHCP in a bigger subnet.

    So, I was thinking about just use X.X.0.0/16 and slowly migrate the static stuff to the new mask (and migrate to DHCP with reservation, of course), but I've read too much good-old advices about "too big domain", "too much broadcast traffic" ecc to use the /16 lightly.

    Do you know about any real issue about using /16 in a LAN? Here it's all modern ubiquiti switches, AP and router. The other machines are fairly new, too.



  • One thing to note is that if you slowly migrate and you have systems that come from beyond the /24, you will get a lot of traffic looking for the gateway to get to that other subnet. I went from a /24 to a /22 several years ago and am still good to go.

    Whichever way you go, make sure that you adjust your DHCP lease times to a very brief time so that they will get the new IP scheme sooner than later.

    Edit: adjust the DHCP lease times far enough in advance so it will make a difference. After they all have new leases with the new scheme, you can lengthen the lease time.



  • A /16 seems pretty drastic when coming from a /24



  • @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.



  • @wrx7m said in Any reason to avoid /16 in 2017?:

    One thing to note is that if you slowly migrate and you have systems that come from beyond the /24, you will get a lot of traffic looking for the gateway to get to that other subnet. I went from a /24 to a /22 several years ago and am still good to go.

    Whichever way you go, make sure that you adjust your DHCP lease times to a very brief time so that they will get the new IP scheme sooner than later.

    Edit: adjust the DHCP lease times far enough in advance so it will make a difference. After they all have new leases with the new scheme, you can lengthen the lease time.

    Very helpful tips, thank you!



  • @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.



  • @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.

    Ok, but I think the broadcast traffic depends only on the number of hosts in the subnet. I wouldn't put more than ~500 active IPs in this subnet, ever.



  • With only 350 network devices, he can have a /8 and it wouldn't make any difference over a /22. The number of devices is what matters. If you have a /8 and only 1 computer... who cares?

    It only becomes a problem when you actually do have so many network devices on a single subnet that the broadcasts can be overwhelming. This won't be the case with him, at least not anytime soon as far as we know.

    If a time comes where you will be adding more devices, just create a new subnet, for the new devices....

    or in the meantime...

    Add devices strategically, as well as controlling what IPs your DHCP server hands out. You can still limit it to a small range so they aren't scattered around. This way, you can shrink it later if needed.



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.

    Ok, but I think the broadcast traffic depends only on the number of hosts in the subnet. I wouldn't put more than ~500 active IPs in this subnet, ever.

    Then you really have no reason to use a /16 over something more reasonable, like a /20 or /22, right?



  • @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.

    Ok, but I think the broadcast traffic depends only on the number of hosts in the subnet. I wouldn't put more than ~500 active IPs in this subnet, ever.

    Then you really have no reason to use a /16 over something more reasonable, like a /20 or /22, right?

    FFS this is not that damned hard.

    Of course he has no reason to use a /16 except that the two existing networks are that far apart. He has clearly stated that he wants to eventually get all the devices into a /21 or so.



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    Hi everyone, I was just thinking about merging two /24 subnet that are like X.X.0.0 and X.X.120.0 (running out of IPs)… some apps that run on that contains weird static-ip configuration (like SAP B1 services with hardcoded IP, CCTV ecc), so I cannot easily reconfigure everything from scratch with DHCP in a bigger subnet.

    So, I was thinking about just use X.X.0.0/16 and slowly migrate the static stuff to the new mask (and migrate to DHCP with reservation, of course), but I've read too much good-old advices about "too big domain", "too much broadcast traffic" ecc to use the /16 lightly.

    Do you know about any real issue about using /16 in a LAN? Here it's all modern ubiquiti switches, AP and router. The other machines are fairly new, too.

    Assuming that both of these networks exist on the same switched network, the only thing you cannot do is to update the router that passes traffic back and forth to be a /16 until all the devices are updated.

    Because as you update devices, they will simply begin to find each other without the router being involved, but all the un updated devices will still require the router to pass traffic back.



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.

    Ok, but I think the broadcast traffic depends only on the number of hosts in the subnet. I wouldn't put more than ~500 active IPs in this subnet, ever.

    Then why go to something so absurdly large instead of just something 2-4x larger than your maximum possible usage?



  • @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.

    Ok, but I think the broadcast traffic depends only on the number of hosts in the subnet. I wouldn't put more than ~500 active IPs in this subnet, ever.

    Then why go to something so absurdly large instead of just something 2-4x larger than your maximum possible usage?

    Again, because there are two production networks that I want to merge together, one is X.X.0.0/24 and the other is X.X.120.0/24. It's hard to rebuild every static-ip-bounded configuration in our small maintainance window, so I plan to change it piece by piece to DHCP reservation, but I cannot do it at one time.

    But, really, what's the problem with the "wasted" space? Is there something intrinsically dangerous or heavy to compute with a /16 network for modern equipment?



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    But, really, what's the problem with the "wasted" space? Is there something intrinsically dangerous or heavy to compute with a /16 network for modern equipment?

    There isn't. If you would make a /1 and put your 350 devices on it, there would be zero difference between that, and if it was a /23.



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @travisdh1 said in Any reason to avoid /16 in 2017?:

    @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @wrx7m said in Any reason to avoid /16 in 2017?:

    A /16 seems pretty drastic when coming from a /24

    Yeah, /16 is too large to actually use. Commonly /23 and /22 are used, they are no problem. In reality, /21 is perfectly fine. Even a /20 is pretty good. But once you start getting into the /19 and larger, you are just getting to some impractically large scales. A /16 is 16,000% larger than a /20, which is generally considered the largest that you can practically use.

    I know this is the common sense, but… what will be the issue? I will have just 300-350 allocated IP, it's just a matter of convenience to include both the X.X.0.0 and the X.X.120.0 range in one big subnet.

    I know it doesn't matter much, but the AWS VPC subnet is /16 by default :D.

    After a certain point, broadcasts overwhelm actual network traffic. That's really the only thing I know that limits the size of a single network.

    Ok, but I think the broadcast traffic depends only on the number of hosts in the subnet. I wouldn't put more than ~500 active IPs in this subnet, ever.

    Then why go to something so absurdly large instead of just something 2-4x larger than your maximum possible usage?

    Again, because there are two production networks that I want to merge together, one is X.X.0.0/24 and the other is X.X.120.0/24. It's hard to rebuild every static-ip-bounded configuration in our small maintainance window, so I plan to change it piece by piece to DHCP reservation, but I cannot do it at one time.

    But, really, what's the problem with the "wasted" space? Is there something intrinsically dangerous or heavy to compute with a /16 network for modern equipment?

    OIC, only thing there is that you already have to touch every static machine to change the gateway, right? And to change the subnet. So where is the effort in fixing the IPs too?



  • @scottalanmiller some machine have complicated configuration that are IP-bounded but not netmask-bounded. The machines on the first subnet are already on DHCP but of course with reservation (that I will maintain unaltered).



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller some machine have complicated configuration that are IP-bounded but not netmask-bounded. The machines on the first subnet are already on DHCP but of course with reservation (that I will maintain unaltered).

    /16 works, seems like weird requirements. But just using a bit range itself doesn't introduce any issues.



  • @francesco-provino said in Any reason to avoid /16 in 2017?:

    @scottalanmiller some machine have complicated configuration that are IP-bounded but not netmask-bounded. The machines on the first subnet are already on DHCP but of course with reservation (that I will maintain unaltered).

    if the machines on DHCP can be moved, then make a /22 network near the second network.



  • The employer I just went to work for was convinced to go from a /24 to a /16 because they were told this was necessary to fix the issues with the VLAN's. The turn up of this was on my 3rd day on the job so I had no idea when I signed on as to why they were making the change. The company has 14 locations on an MPLS but the IP addressing schema is all over the board.



  • @kyle said in Any reason to avoid /16 in 2017?:

    The employer I just went to work for was convinced to go from a /24 to a /16 because they were told this was necessary to fix the issues with the VLAN's. The turn up of this was on my 3rd day on the job so I had no idea when I signed on as to why they were making the change. The company has 14 locations on an MPLS but the IP addressing schema is all over the board.

    LMAO.



  • @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @kyle said in Any reason to avoid /16 in 2017?:

    The employer I just went to work for was convinced to go from a /24 to a /16 because they were told this was necessary to fix the issues with the VLAN's. The turn up of this was on my 3rd day on the job so I had no idea when I signed on as to why they were making the change. The company has 14 locations on an MPLS but the IP addressing schema is all over the board.

    LMAO.

    I'm telling you. The "MSP" is like dealing with psychopathic monkey with alzheimer's.



  • @kyle said in Any reason to avoid /16 in 2017?:

    @scottalanmiller said in Any reason to avoid /16 in 2017?:

    @kyle said in Any reason to avoid /16 in 2017?:

    The employer I just went to work for was convinced to go from a /24 to a /16 because they were told this was necessary to fix the issues with the VLAN's. The turn up of this was on my 3rd day on the job so I had no idea when I signed on as to why they were making the change. The company has 14 locations on an MPLS but the IP addressing schema is all over the board.

    LMAO.

    I'm telling you. The "MSP" is like dealing with psychopathic monkey with alzheimer's.

    lol damn.


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