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Any problem using 172.16.x.x on a LAN ??

Any problem using 172.16.x.x on a LAN ??

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  #1  
Old 18th September 2007, 20:00
WillScog WillScog is offline
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Default Any problem using 172.16.x.x on a LAN ??

I would like to pose a network address question. My company is merging with another company, so we will be on the same LAN and subnet. We both have 192.168.xx addresses at the moment, but when we merge, we are expected to all have the same addressing scheme which is 192.168.125.x. Combined we will need approx. 240 host addresses, close to the max on such a subnet.

Before I go to my senior networking consultant to request a change to 172.16.x.x addressing, which is what would be the next logical step if we care to grow at all in the future, does anyone see any problems with changing from a Class C non-routable, reserved network address to a Class B address such as 172.16.0.0 for our new LAN in a new building? It seems that setting up a new LAN in a new building is the ideal time to change the addressing scheme.

Every class has a set of addresses reserved for LANís, I donít know why any administrator would use 192.168.0.0 to begin with since you are starting out with a limitation of 254 hosts. I inherited my address scheme which is 192.168.139.0. 254 sounds like a lot, when I first started I had 11 workstations, and now, 7 years later I will have 240. You never know how much youíre going to grow.

Sorry this is so long. Is there any reason why a network administrator canít use 172.16.0.0 with a subnet address of 255.255.0.0 for a LAN? That should give me 64 thousand possible hosts instead of 254.
Thanks in advance, Will
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Old 18th September 2007, 20:36
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Default Re: Any problem using 172.16.x.x on a LAN ??

I don't see any problem with using 172.16.x.x ... but is there any reason you can't supernet the two class C networks together? i.e. give it a 255.255.0.0 (/16) mask... or even a 255.255.252.0 (/23) which is 510 hosts. Do you have some really old equipment you're using that would prevent you from supernetting?

The other option is to route between the subnets. Although you said 192.168.0.0 is not routable, it is really just not routable over the Internet. 172.16.0.0 cannot be routed over the Internet either.
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Old 18th September 2007, 20:57
WillScog WillScog is offline
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Default Re: Any problem using 172.16.x.x on a LAN ??

That is possibly a good idea, keeping the same IP addresses and changing only the subnet address. Although it seems to be the same amount of work as setting up an address scheme using default subnet addresses. However, 90% of our hosts get their IP, subnet, and gateway addresses from the DHCP server so it would be easy to change there. I don't have any legacy equipment that I couldn't do that on. I do have a NAS server which is difficult to get to the network configuration to change the addresses, but it would be the same amount of work to change the IP address as to change the subnet address.

I really do appreciate your response, however I am having a difficult time seeing an advantage of supernetting in this case since you have to change the configuration of all systems anyway. Still open to suggestions, and I will pose your solution to the decision maker.
Thanks, Will
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Old 18th September 2007, 21:12
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Default Re: Any problem using 172.16.x.x on a LAN ??

You're right, there's no real advantage other than that you are already familiar with your equipment's static IP addresses. Also, if you have any manual entries in DNS, you wouldn't need to update them.
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Old 18th September 2007, 21:38
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Default Re: Any problem using 172.16.x.x on a LAN ??

Thanks again Jeremy, that's a good point.
I really like your quote from Elliot.
Will
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Old 19th September 2007, 02:26
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Default Re: Any problem using 172.16.x.x on a LAN ??

I agree that changing the subnet mask is just as much work as changing the host address. I would recommend using a 10.x.x.x/8 addressing scheme as this allows for a bazillion (not really) host addresses and allows for creating a standard addressing scheme such as using 10.1.x.x for routers, 10.2.x.x for switches, 10.3.x.x for servers, etc., etc.
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Old 19th September 2007, 10:00
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Default Re: Any problem using 172.16.x.x on a LAN ??

Why joeqwerty why?????
I really don't understand why anyone would recommend a /8 subnet if he doen't need it. Do you expect that they grow to 16.777.214 hosts?
If not, why do you need a /8?
You create a lot of management overhead.

If they have grown in 7 years from 11 clients to 240 clients, do you expect they will grow out to accomodate 254 servers, 254 routers, 254 switches etc?

Personally i would go for the supernetting option and use the /22 (255.255.252.0) which gives you 1022 addresses.
(i used http://www.subnet-calculator.com/ for quick calculation)
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Old 19th September 2007, 14:17
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Default Re: Any problem using 172.16.x.x on a LAN ??

Why not? It's a private network so who cares what range is used? Is the 10.x.x.x range evil? A 10.x.x.x range gives you the most possible host addresses and allows you to be creative in creating addresses based on device class. Can you explain to me why you think it is more management overhead, because from a technical perspective there is no more management overhead using 10.x.x.x than any other address range. They will have some work to do in implementing it but after it's done they'll have the same management overhead as they would using any address range. In my opinion most companies need few networks but many hosts and using a 10.x.x.x range insures that they will never run out of host address space. Supernetting is an option but why make it confusing for the guy. IMHO, Just because you CAN make something complicated doesn't mean you SHOULD. Pardon my use of caps.
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Old 19th September 2007, 15:29
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Default Re: Any problem using 172.16.x.x on a LAN ??

If you use a /8 network (only 10.0.0.0's private range is big enough for this) you've gobbled up all your IP addresses in one fell swoop. They're all in the same broadcast domain and if you get a second location then you'll have to use 172.16 - 32 or 192.168 IPs. And you could never just move a segment to another physical location (over a WAN link) without a lot of work.

Plus, there is a practical limit to the number of hosts in a single broadcast domain. Too many hosts on one segment will bog down the traffic.

Besides, you can do essentially the same thing with a /16 network (10.1.1.0 servers; 10.1.2.0 routers; etc.) but I still don't think it's necessary.


There is a reason most people do things a certain way. I wouldn't go changing things until you know why they do it that way.
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Old 19th September 2007, 17:43
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Default Re: Any problem using 172.16.x.x on a LAN ??

Agree with Jeremy.
You will create one big broadcast domain.
Without subnetting it, you will create a lot of broadcast traffic, especially when they put more hosts in the network.

You know, a broadcast domain is only been split by a router or a bridge. So using a 10.x.x.x /8 subnet will create only one broadcast domain which cannot be split.

For example:
You have 1000 servers, 8000 clients, 200 printers, and 100 switches and about 10 routers.
If you use 10.x.x.x /8 subnet all those 9310 machines will broadcast. All machines needs to process that broadcast packet (eg arp) which costs CPU power.
In the end you're network performance will degrade.

If you subnet this, you can split this /8 in multiple smaller portions (hey subnets ) When you start using VLANS you can route between them.

A nice article about broadcasting:
http://support.novell.com/techcenter...c2000_10c.html

So using the private range 10.x.x.x /8 isn't evil as long as you know what and why subnetting is that important.

With management overhead i mean you will lose any network sight in the end.
Nobody will tell you to put a server into another range then where the others are placed. If you get replaced or you get a new colleague he will make this mistake.
With so many useless IP-addresses you just get lost in the end.

Only great documentation and procedures will hold this. However who has a great IP scheme?
From my workplace i can tell you: so far nobody has a great ip scheme

This must be worth some reputation points
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