DNS Server not visible in other subnets

[CHR1S]

My DHCP server dishes out IP's to 3 subnets - 192.168.0/1/2

 

It has the correct settings for DNS and Router.

 

Any PCs in the 192.168.0.* subnet work perfectly.

 

Those in the 192.168.1/2.* subnets get assigned the router and DNS but cant ping them.

 

Whats the obvious mistake I have made and missed?

 

Thanks

 

Chris

[Guest Guest]

Are the DNS and router IPs the same for all subnets? Subnets using a mask of 255.255.255.0? If so it sounds like the router and DNS are on the 192.168.1.x network, hence why that network works.. The other 2 subnets are different networks and need a router on their network to pass traffic to the 192.168.1.x network. Edited November 8, 2012 by Guest

[CHR1S]

Ive reduced my scope to 192.168.0.* only as I dont need that many addresses so the issue is redundant now.

However my subnet mask is 255.255.252.0 - could that be it?

[glennda]

Ive reduced my scope to 192.168.0.* only as I dont need that many addresses so the issue is redundant now.

However my subnet mask is 255.255.252.0 - could that be it?

 

that would give you 4 addresses?

[CHR1S]

that would give you 4 addresses?

 

That would be 255.255.255.252

 

255.255.252.0 should allow 4 class C's

[glennda]

That would be 255.255.255.252

 

255.255.252.0 should allow 4 class C's

 

Sorry my bad - i read it totally wrong! I presume they are all on the same Vlan? or different vlans?

 

The router and DNS servers have the correct subnets specified themselves?

[CHR1S]

No Vlans - Router and DNS are specified in the scope options and server options.

[FN-GM]

No Vlans? This will be the problem. Are you sending out different ip ranges and subnets on a "flat network".

[CHR1S]

Its my home/test/experiment network - just unmanaged switches

[FN-GM]

Its my home/test/experiment network - just unmanaged switches

 

That will be the issue then. If you want to have different subnets you need to split them up. You can do this by either separate physical switches or VLANs. Then you need to route between these networks by using a layer 3 switch or a router.

[CHR1S]

So you cant assign more than one lot of 256 addresses without L3 switches?

[FN-GM]

You dont need a layer 3 switch you just need to have 1 scope with a different subnet mask

 

255.255.255.252.0 will give you 1022 addresses but you need to use a class b range 172.x.x.x - see here Online IP Subnet Calculator

 

The reason for vlans and a layer 3 switch is to spilt the subnets up into chunks. This limits broadcast traffic and makes things run better.

[FN-GM]

You was right about the subnet mask up there, i read that bit but it didnt go in

[CHR1S]

So, let me try and get my head around it -

 

If I swap out the 192.168.0.0 for a 172.168.0.0 with a 255.255.252.0 mask it should allow me to dish out 4 subnets?

 

172.168.1/2/3.0 ?

[FN-GM]

172.168.x.x isnt a private range us something between this range - 172.16.0.0 - 172.31.255.255

 

If you use 172.16.0.1 with a subnet mask of 255.255.255.252 it will give you the range of 172.16.0.1 - 172.16.3.254 a total of 1022 addresses.

 

In your DHCP just create one scope with these settings.

[CHR1S]

I created the scope the same way with the 192.168 and it dished out IP addresses just fine.

Will this solve the DNS issues?

[FN-GM]

Whats the subnet mask?

[CHR1S]

255.255.252.0

[FN-GM]

should be ok for the first 256 addresses after that i would probably not

[CHR1S]

Thanks for the lesson. I will experiment some more.

[Guest Guest]

Try not to concern yourself with classes, since supernetting became the norm that terminology is no longer relevant. For example you can supernet your class C range (192.168.x.x) by using a class B type mask (255.255.252.0) - so what is it; class B or class C? See how classes become blurred into each other, hence why people tend not to use that terminology anymore (yes I know books do but thats theory based on 80/90s tech)

 

There is no reason why the above won't work so long as everything has the same subnet mask: 192.168.0.0-192.168.2.255 with mask 255.255.252.0 is one network/subnet/supernet.

 

You don't NEED a L3 switch or vlans to have different subnets on the same physical network. In production, as FNGM said, the reason is to limit broadcasts and to segregate the network for security. For testing you can just pretend its vlaned.

 

 

If you want to read more about the replacement to classes - http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing

Edited November 9, 2012 by Guest