[buug] DSL 768/768 line with 5 IP's

Michael Paoli Michael.Paoli at cal.berkeley.edu
Sun Jun 4 15:36:07 PDT 2006

Quoting Al Plant <webmaster at hawaiidakine.com>:
> We have acquired a DSL Line 768/768 with 5 ip addresses to learn on with
> 66.xxx.xxx.234 .235 .236 .237 .238
> a Sub netmask of 66.xxx.xxx.248
> And a Gateway of 66.xxx.xxx.233
> The Tech person at the providers end however did not know how I would
> connect and whether the Gateway was mine or there end.
> I have a Farallon switch and a Freesco Router to connect the servers to
> the incoming/outgoing dsl modem and to the (possible) 5 Servers.

That's a relatively common scenario for multiple static IPv4 IPs over DSL.
There's a /29 mask -
There are 8 IPv4 IPs, 5 "useable", and the remaining 3 being the IP for
the network itself, the router, and the broadcast address, respectively.
netmask: (/29)                11111000
network:     66.xxx.xxx.232 (/29)                11101000
gateway:     66.xxx.xxx.233 (default route(r))   11101001
IPv4 1:      66.xxx.xxx.234                      11101010
IPv4 2:      66.xxx.xxx.235                      11101011
IPv4 3:      66.xxx.xxx.236                      11101100
IPv4 4:      66.xxx.xxx.237                      11101101
IPv4 5:      66.xxx.xxx.238                      11101110
broadcast:   66.xxx.xxx.239                      11101111
Sometimes it's a bit easier to see in binary - I included the last
octet in binary above.
The gateway is on "their" end, ... otherwise you wouldn't make it off
of your subnet.
Configuration's relatively straight-forward - set up the netmask, IP,
broadcast, default route, DNS configuration, and in some cases also
network address, for each device - or configure a DHCP server to hand
them out (or some of both).  They should also give you the IPs of DNS
server(s) to use.  Just need a hub or switch between the DSL modem
and the other devices, don't need any fancy NAT/SNAT/masquerading,
etc., unless you don't want the IPs directly reachable from The
Internet and/or need to simultaneously use more than 5 IPv4 devices.
Having the multiple static IPs is generally preferable to a single IP
and multiple devices, but the ISP will typically charge somewhat more
for that.

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