04-04-2012 04:31 AM - edited 03-07-2019 05:57 AM
What are the rules for vlsm assignment for ip planning..
For example;
In my office I assigned that network address to one subnet of Router A:
192.168.3.11100000/27
Say; one of the host's ip address is : HOST1: 192.168.3.11100010 /27
But in the same office I assigned different vlsm to another subnet of different router, say, Router B:
192.168.3.11100010 /29
If one of the host of this network wants to communicate with HOST1(192.168.3.11100010) It can't happen because after mask anding, it thinks it is in the same lan.
so there is a collision here.
Right?
So what are the rules for ip planning with different vlsm? How can we avoid such collisons?
04-04-2012 05:58 AM
Don't really understand your ip addresses but I gress the last 8 digits there is a binary representation of the final octet of the ip address.
Yes, you have a conflict, the /27 overlaps the /29 and whoever is on or connects with the /27 net will beleive the /29 net you are using is local thus no routing possible.
The /27 represents the netmask 255.255.255.224 and is a block of 32 addresses.
The /29 represents netmask 255.255.255.248 and is a block of 8 addresses.
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04-04-2012 06:32 PM
sawquecisco wrote:
What are the rules for vlsm assignment for ip planning..
For example;
In my office I assigned that network address to one subnet of Router A:
192.168.3.11100000/27
Say; one of the host's ip address is : HOST1: 192.168.3.11100010 /27
But in the same office I assigned different vlsm to another subnet of different router, say, Router B:
192.168.3.11100010 /29
If one of the host of this network wants to communicate with HOST1(192.168.3.11100010) It can't happen because after mask anding, it thinks it is in the same lan.
so there is a collision here.
Right?
So what are the rules for ip planning with different vlsm? How can we avoid such collisons?
Find someone who actually knows IP and does the design for you.
Or download something like the Solar Winds advanced IP subnet calculator and check if your subnets overlap before putting them into your design.
Cheers.
04-13-2012 06:25 AM
Hi sawquecisco,
Keep in mind this:
(for the following examples, we suppose that the network root is 192.168.0)
You can have on network A machines with IP@ .1,.2,.3,.4,.5,.6,.30, and on network B machines with IP@ .33,.34,.35,.36,.37,.38,.60. But it will be an error if you use addresses .16,.17 for network B. Idem if you use .40, .50 or .59 in network A.
subnetwork A: @IP : .1 -----------------------------. 31
subnetwork B: @IP : .16-----------------------------.63
not good!
You can not use (sub)network addresses .1 to .31 on a network A and use addresses .16 to .63 for network B. In this
case, IP@ .16 to .31 are on the TWO networks!
You can use subnetwork .0/27 on network A, .32/27 on network B. A router that federate this network can use .0/26 to manage routes for this two networks. (in /27, the IP@ by networks are .1 to .31 ; .32 to .63 ; .64 to .95 ; etc, while in /26 they are .0 to .63; .64 to .127; etc).
Complement:
Suppose that you have the following 4 others networks with /28 :
IP@ for network C: .64 to .79;
IP@ for network D: .80 to .95;
IP@ for network E: .96 to .111;
IP@ for network F: .112 to .127
the route 192.168.0.0/25 will federate network A to network F
Hope that will help you.
sadavir-ap-sampath.
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