Reserved IP blocks and subnets...

Posted on 2002-07-15
Medium Priority
Last Modified: 2007-02-12
I am implimenting VPN on a client network with LAN subnet on the reserved IP block  10.xxx.xxx.xxx

Since this is a Class A IP block..I would assume the subnet to be But they are using

Is this a right thing to do ? Though their network is functioning properly as of now, will it create issues later on for Internetworking or VPN connectivity with other networks?

Pls refer if you a link to any authentic docs on this (Like RFC)

Question by:ferose

Expert Comment

ID: 7154227
ip address classes are not decided on the basis of subnet masks, but on the first few reserved bits

for class A - first bit always zero
for class B - first 2 bits 10
and so on...

also the range 10.xx.xx.xx may be split up into many subnetworks, hence the extended subnet mask

Accepted Solution

edmonds_robert earned 200 total points
ID: 7154245
This will not cause any problems at all.  Take for example the IP block you got from your ISP for your outside addresses.  Depending on the size of the organization, you probably got a class C IP address but didn't use the default class C subnet mask of  The default is just that, default.  It can be changed to match your organization's structure.  If you don't need to have more that 254 hosts on a subnet, why use a shorter subnet mask?  For example, we use 172.16.x.x in our organization, but use the subnet mask also.  

As another example, conisder leased line configuration.  Most people will use the subnet mask as the subnet mask on a leased line to conserve IP address space.  As long as your network equipment supports VLSM (Variable Lengt Subnet Masking), you can use any combination of subnet masks on your network that you please.  

Author Comment

ID: 7156240
Thanx edmonds:  That settles it without question..


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