[NTLUG:Discuss] Broadcast IP address

[Eric Schnoebelen]

Ralph Green writes:
- Howdy,
-   I have a network I want to expand a bit with as little impact on the
- users as possible.  All LAN addresses are currently in the 192.168.4.x
- range.  I am adding a new VPN server and I am thinking of using
- 192.168.5.1 for its address.  It looks like I need to adjust the
- netmask on machines in the original LAN from 255.255.255.0 to
- 255.255.254.0.  If I do that on a test machine, I can reach it from
- the 192.168.5.x machines.  I see the broadcast address has changed
- from 192.168.4.255 to 192.168.5.255.  If I make the netmask change on
- the servers, including the DHCP server, will clients be able to renew
- their leases?

Most DHCP servers/clients try to renew their leases with a
directed request to the DHCP server they received their lease
from.

-  I am thinking they will broadcast on 192.168.4.255 to
- get a renewal and they won't find a response.

No, see above. They will broadcast to 255.255.255.255 when they
request an initial lease though.

-  What would be a good way to resolve this?

I don't think it's an issue with the supernetting.

-  The only thing I can think of offhand, is maybe
- to add a new machine temporarily at 192.168.4.255 and forward packets
- to 192.168.5.255, but I think that might be a bad IP address for a
- machine on the network.
- Do you have any suggestions,

Why not route between the LAN (local workstation) and VPN
subnets?

Otherwise, it sounds like a proxy-arp storm waiting to happen.

--
Eric Schnoebelen		eric at cirr.com		http://www.cirr.com
   In God we Trust -- all others must submit an X.509 certificate.
                        -- Charles Forsythe