Solved

class c subnet on class b subnet

Posted on 2010-11-16
9
603 Views
Last Modified: 2012-05-10
Can a class c subnet be on the same network as a class b subnet.
class b address 10.10.1.1 255.255.0.0 ( not using the class c addresses )
class c address 10.10.10.1 255.255.255.0
i think the answer is no but wanted to see if anyone had used this configuration.
0
Comment
Question by:tad91030
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
9 Comments
 
LVL 11

Assisted Solution

by:MajorBigDeal
MajorBigDeal earned 166 total points
ID: 34151780
Yes, you can do this because the most specific route will win.  In other words, routes do not have to be defined to be completely mutually exclusive (although I think it is better if they are).  In those cases where more than one subnet matches, the router will attempt to figure out which route is the most specific and use that one.
0
 
LVL 14

Expert Comment

by:Otto_N
ID: 34153956
To add to MajorBigDeal's comment:  Yes, you can, but it just open up opportunities for confusion.  Also, if you want devices in the separate subnets to talk to each other, it will not work.
0
 
LVL 14

Accepted Solution

by:
Otto_N earned 168 total points
ID: 34154284
Just to explain, if you have overlapping subnets, why communication between the subnets will fail. Let's use the subnets in the example:
Subnet1 - 10.10.0.0/16
Subnet2 - 10.10.10.0/24

If you have a host in each subnet (Host A with IP 10.10.1.5 in Subnet1, and Host B with IP 10.10.10.15 in Subnet2), and A want to send an IP packet to B, the following will happen:
i) A will query its routing table and see that, to reach 10.10.10.15, it needs to use a specific interface, let's say eth0.
ii) The IP stack in host A will next check if the destination address is in the same subnet than eth0.  To do this, it compares the result of the bit-wise AND of the IP address and subnet mask of eth0 (10.10.1.5 AND 255.255.0.0 = 10.10.0.0 for this example) with the bit-wise AND of the destination IP address and the subnet mask of eth0 (10.10.10.15 AND 255.255.0.0 = 10.10.0.0). If it is the same, it send it to Layer2 for direct delivery; if not, it send it to Layer2 for delivery to the default gateway.

Since, from host A's point of view, eth0 is in the same subnet as host B, A will issue an ARP request for B's MAC address (assuming we're using Ethernet).  But B will not receive this broadcast, since it is in a different segment, and A will not receive a response.  Even if you configure proxy-ARP on your router, it will not help, since the router is also configured with the 255.255.0.0 mask for the interface in segment1.

This can be fixed with a static route on host A, directing traffic destined for Subnet2 to the default gateway, but this is a manual process that must be implemented on every host that need to communicate with Subnet2, and would not be recommended.
0
Supports up to 4K resolution!

The VS192 2-Port 4K DisplayPort Splitter is perfect for anyone who needs to send one source of DisplayPort high definition video to two or four DisplayPort displays. The VS192 can split and also expand DisplayPort audio/video signal on two or four DisplayPort monitors.

 
LVL 2

Assisted Solution

by:pmanno
pmanno earned 166 total points
ID: 34157199
Just as a side note, classes pertain to IP addresses, not subnets.  What you have is a class A IP address that you are subnetting.  By subnetting you are not changing the class.  the class is determined by the location of highest order 1s in the first octet.  For example:

Class A First Octet = 0XXX XXXX
Class B First Octet = 10XX XXXX
Class C First Octet = 11XX XXXX

Ref: http://en.wikipedia.org/wiki/Classful_network

0
 

Author Comment

by:tad91030
ID: 34158843
any suggestions for routers. we have an rv082 but it only allows class c mask.
0
 
LVL 11

Expert Comment

by:MajorBigDeal
ID: 34167809
That is a problem.  You'll either have to use a second router or else rework your network. Sorry!
0
 
LVL 11

Expert Comment

by:MajorBigDeal
ID: 34769641
Any Luck?
0
 
LVL 70

Expert Comment

by:Qlemo
ID: 35015601
This question has been classified as abandoned and is being closed as part of the Cleanup Program. See my comment at the end of the question for more details.
0

Featured Post

Connect further...control easier

With the ATEN CE624, you can now enjoy a high-quality visual experience powered by HDBaseT technology and the convenience of a single Cat6 cable to transmit uncompressed video with zero latency and multi-streaming for dual-view applications where remote access is required.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

If you're not part of the solution, you're part of the problem.   Tips on how to secure IoT devices, even the dumbest ones, so they can't be used as part of a DDoS botnet.  Use PRTG Network Monitor as one of the building blocks, to detect unusual…
This article is in regards to the Cisco QSFP-4SFP10G-CU1M cables, which are designed to uplink/downlink 40GB ports to 10GB SFP ports. I recently experienced this and found very little configuration documentation on how these are supposed to be confi…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Monitoring a network: why having a policy is the best policy? Michael Kulchisky, MCSE, MCSA, MCP, VTSP, VSP, CCSP outlines the enormous benefits of having a policy-based approach when monitoring medium and large networks. Software utilized in this v…

636 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question