Hot Downloads

Welcome, Guest
Username: Password: Remember me

TOPIC: Determining Network ID

Determining Network ID 9 years 11 months ago #19198

  • skylimit
  • skylimit's Avatar
  • Offline
  • Distinguished Member
  • Posts: 158
  • Thank you received: 1
  • Karma: 0
Hi all, I have this /27 bit IP address (ie 235.85.105.64/27) which I think is a subnet address [pls correct me if im wrong] and Im trying to determine the network ID. I understand that to do this you carry out a bitwise AND of the IP (235.85.105.64) and the subnet mask (255.255.255.224). The network ID i obtain is 235.85.105.1 which i reckon is incorrect. anyone able to help me out here please? thanks in advance.

edit: Im not sure whether to use 255.255.255.0 for the AND operation or 255.255.255.224.

secondly will I be right to say the above address is a subnet address with 30 valid IPs even when it falls in the range of a class D (multicast address) - im a bit confused pls help?
"...you are never too old to learn" anon
The administrator has disabled public write access.

Re: Determining Network ID 9 years 11 months ago #19206

  • Smurf
  • Smurf's Avatar
  • Offline
  • Moderator
  • Posts: 1390
  • Karma: 1
The address that you have identified is the network ID portion. So 235.85.105.64/27 is the networkid giving valid address from;

235.85.105.65 - 235.85.105.94 = 30 host address

255.255.255.224
11111111.11111111.11111111.111 00000

If we look at the last octet

64 = 010 00000

The Host portion is all 0's therefore we are looking at a network ID. The first valid host address = 010 00001 The last valid host address = 010 11110 (because 010 11111 is the broadcast address)
Wayne Murphy
Firewall.cx Team Member
www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit www.sec-1.com or PM me for details.
The administrator has disabled public write access.

Re: Determining Network ID 9 years 11 months ago #19208

  • skylimit
  • skylimit's Avatar
  • Offline
  • Distinguished Member
  • Posts: 158
  • Thank you received: 1
  • Karma: 0
thanks for your fast reply. am i right to say we can have 8 subnets (i.e. 000, 001......111). or 6 subnets without (i.e. 000 and 111) im a bit confused about this. any responses appreciated.
"...you are never too old to learn" anon
The administrator has disabled public write access.

Re: Determining Network ID 9 years 11 months ago #19210

  • Smurf
  • Smurf's Avatar
  • Offline
  • Moderator
  • Posts: 1390
  • Karma: 1
Yes, thats correct. You have 3 bits for the NetworkID which is therefore 2^3 = 8. As you said, normally you cannot use the first and last so you will often see 2^3-2=6

If you take a look at this post here, StarFire confirms that in todays routers that support Subnet 0, this is allowed but for CCNA, etc... you still need to include the -2 rule.

Cheers
Wayne Murphy
Firewall.cx Team Member
www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit www.sec-1.com or PM me for details.
The administrator has disabled public write access.
Time to create page: 0.077 seconds

CCENT/CCNA

Cisco Routers

  • SSL WebVPN
  • Securing Routers
  • Policy Based Routing
  • Router on-a-Stick

VPN Security

  • Understand DMVPN
  • GRE/IPSec Configuration
  • Site-to-Site IPSec VPN
  • IPSec Modes

Cisco Help

  • VPN Client Windows 8
  • VPN Client Windows 7
  • CCP Display Problem
  • Cisco Support App.

Windows 2012

  • New Features
  • Licensing
  • Hyper-V / VDI
  • Install Hyper-V

Linux

  • File Permissions
  • Webmin
  • Groups - Users
  • Samba Setup