Adding new subnets

[Guest]

We are going to be opening our first branch office and thus are going to set
up a new subnet for that office. The two networks will connect via a point
to point T1 connection. Our current DHCP scope at the main office is setup
as 10.1.1.0 with a subnet mask of 255.255.255.0. In order for the two
networks to talk to each other I am going to change the subnet mask on our
current scope to 255.255.248.0. There will be another DHCP server in the new
office that will allocate ip addresses for those clients. Its scope will be
10.1.4.0 (i am leaving room for other subnets at the main office) with the
same 248 mask. My question is: Am i doing this right? Do i only really
need to change the subnet mask on our current DHCP server in order for the
two networks to communicate?

Thanks!!

 

[Phillip Windell]

We are going to be opening our first branch office and thus are going to set
up a new subnet for that office. The two networks will connect via a point
to point T1 connection. Our current DHCP scope at the main office is setup
as 10.1.1.0 with a subnet mask of 255.255.255.0. In order for the two
networks to talk to each other I am going to change the subnet mask on our
current scope to 255.255.248.0.

No. Keep it simple. Stay with a straight 24bit mask (255.255.255.0).
Ethernet becomes less efficient above 250-300 hosts (your mileage may vary).
The 24 bit mask provides 254 hosts which is perfect. Create new subnets by
simply incrementing the third Octect by 1.

10.1.0.0 255.255.255.0
10.1.1.0 255.255.255.0
10.1.2.0 255.255.255.0
10.1.3.0 255.255.255.0
10.1.4.0 255.255.255.0

Am i doing this right? Do i only really
need to change the subnet mask on our current DHCP server in order for the
two networks to communicate?

No it doesn't have anything to do with it. All that does is add more
addresses to the same subnet. So you still have one subnet that is just
bigger and less effiecient.

You can not have subnets without a LAN Router to route between them. If you
can't afford the router,..then you can afford the subnets. But if the bank
can afford to build a new branch,...they can afford a LAN Router,...don't
let them tell you they can't. You can't build a network with duct tape and
baling wire,..you have to buy the right equipment for the job.

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/ISA2004_AccessRules.html

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/techinfo/Guidance/2004.asp
http://www.microsoft.com/isaserver/techinfo/Guidance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp
-----------------------------------------------------

 

[Guest]

Thanks for your reply! We already have routers for the point to point
connection so just keeping the mask at 255 across the board, should the
routers be configured correctly, connect the 10.1.1.0 and 10.1.4.0 networks.
When we decide to add additional subnets to our main site i am assuming the
routing can be taken care of via our switches that do layer 3 switching and
VLANs. Is it wrong to assume this?

We are going to be opening our first branch office and thus are going to set
up a new subnet for that office. The two networks will connect via a point
to point T1 connection. Our current DHCP scope at the main office is setup
as 10.1.1.0 with a subnet mask of 255.255.255.0. In order for the two
networks to talk to each other I am going to change the subnet mask on our
current scope to 255.255.248.0.

No. Keep it simple. Stay with a straight 24bit mask (255.255.255.0).
Ethernet becomes less efficient above 250-300 hosts (your mileage may vary).
The 24 bit mask provides 254 hosts which is perfect. Create new subnets by
simply incrementing the third Octect by 1.

10.1.0.0 255.255.255.0
10.1.1.0 255.255.255.0
10.1.2.0 255.255.255.0
10.1.3.0 255.255.255.0
10.1.4.0 255.255.255.0

Am i doing this right? Do i only really
need to change the subnet mask on our current DHCP server in order for the
two networks to communicate?

No it doesn't have anything to do with it. All that does is add more
addresses to the same subnet. So you still have one subnet that is just
bigger and less effiecient.

You can not have subnets without a LAN Router to route between them. If you
can't afford the router,..then you can afford the subnets. But if the bank
can afford to build a new branch,...they can afford a LAN Router,...don't
let them tell you they can't. You can't build a network with duct tape and
baling wire,..you have to buy the right equipment for the job.

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/ISA2004_AccessRules.html

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/techinfo/Guidance/2004.asp
http://www.microsoft.com/isaserver/techinfo/Guidance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp

 

[Doug Sherman [MVP]]

If you want to do conventional routing over this connection, then the main
office and the branch office need to be on different subnets. However,
unless you are running out of addresses on the 10.1.1.0 network, there is no
need to change the subnet mask. 10.1.1.0 and 10.1.4.0 with subnet masks of
255.255.255.0 are different logical subnets. 10.1.1.0 and 10.1.4.0 with
subnet masks of 255.255.248 are on the same subnet. If you want to use a
mask of 255.255.248, make the branch office 10.1.8.0.

Doug Sherman
MCSE, MCSA, MCP+I, MVP

 

[Phillip Windell]

Thanks for your reply! We already have routers for the point to point
connection so just keeping the mask at 255 across the board, should the
routers be configured correctly, connect the 10.1.1.0 and 10.1.4.0

networks.

From what little I know at this point,...yes.

When we decide to add additional subnets to our main site i am assuming the
routing can be taken care of via our switches that do layer 3 switching and
VLANs. Is it wrong to assume this?

If they are Layer3 Switches then yes,...such a Switch is really a Router and
a Switch built into the same "box". I really wish they would have came up
with a new name for those to avoid the Switch vs Router confusion,...but
they didn't ask me ;-).

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/ISA2004_AccessRules.html

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/techinfo/Guidance/2004.asp
http://www.microsoft.com/isaserver/techinfo/Guidance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp
-----------------------------------------------------