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dangiz

@216.52.x.x

5 Static IP's on a /30 subnet?

I just signed up for SBC DSL with 5 Static IPs. Received the configuration sheet from them, which shows my WAN addresses as follows:
WAN Gateway: X.X.X.145
First Usable: X.X.X.146
Subnet Mask: 255.255.255.252

I looked at this and assumed that the SM was wrong, so I called SBC. They tell me that the SM is correct, but can't tell me how to get 5 IP's thru a 4 IP hole.
Seems to me that this SM would give me .144, .145, .146 and .147. Given .145 for the SBC gateway, that leaves me with
.146 and .147 only. If I assign .146 to my router, I'm now left with .147. What am I missing here?
It sure seems like the correct SM would be .248.

I did receive a block of LAN addresses which I assume are a routed subnet used to access the SBC account info, etc. Not sure what else they are used for.
They do have the .248 SM as I would expect. If I take off one address for the net, one for the gw and one for the bcast, it leaves me with the expected 5 addresses.

Router is a Cayman 3546.

Thanks

(post was moved from the networking forum)


pflog
Bueller? Bueller?
Premium,MVM
join:2001-09-01
El Dorado Hills, CA
kudos:3
No, their subnet mask is incorrect. You are correct, it should be .248 for a /29 CIDR (5 usable IP addresses).

I think you can assume your usable IPs are:

.146
.147
.148
.149
.150

With .145 being your "WAN IP", .151 your gateway and .152 your broadcast.

Easy 8

join:2002-12-18
Plano, TX
reply to dangiz
The way this should work is as follows:

.144 - network address (not useable)
.145 - gateway addrees (ip of interface on SBCs redback)
.146 - WAN interface IP (address assigned to your router's WAN interface)
.147 - broadcast address (not useable)

You then would use one of the IPs from the /29 as the address for your router's ethernet interface and the remainder of the useable IPs in the /29 for your LAN devices.

Does that make sense?

Matthew
Premium,VIP
join:2001-08-03
Emmett, ID
reply to dangiz
That is your WAN side IP assigned to your Cayman. There should also be an accompanying LAN cidr that has your 5 IP's. You would replace the current default LAN side IP's (the 192.168.0.1) with the .248 subnet and IP stack you were assigned to use the 5 IPs you ordered.
--
It truly is the lowest level where we ALL make the difference.


pflog
Bueller? Bueller?
Premium,MVM
join:2001-09-01
El Dorado Hills, CA
kudos:3
reply to Easy 8
with a /30, wouldn't it be:

.144 - network (non-usable)
.145 - first usable IP
.146 - WAN gw
.147 - broadcast

In any case, SBC doesn't sell /30 CIDRs, only /29 so the netmask is a mistake in the email.

Matthew
Premium,VIP
join:2001-08-03
Emmett, ID
Actually, it is not a mistake for this order. If you order the static package with a router that is how it is built. There is a WAN side assignment, and a LAN side assignment. The WAN side is a single IP, and the LAN side is whatever is purchased (from 5 use- ables on up).
--
It truly is the lowest level where we ALL make the difference.


dangiz

@216.52.x.x
reply to Matthew
Now it makes sense. The SBC person I spoke to gave me the WAN addresses .146-.150 and told me they were my public addresses. In fact, I already have them entered into the DNS. Thanks to all for setting me straight!