/30 ip block 4

[lawcore]

I'm a little confused.

I have a IP Block of 4 from my ISP.

So 2 usable IP's

But I am able to define the gateway IP within the router and use it giving me a total of 3 IP's

Is this correct? I'm a tad confused as I was only aware you could only use 2 of the IP's

Any advise?

 

[frowertr]

I don't follow you. Yes, a /30 will only give you two usable addresses.

What is the full IP address block you were assigned?

 

[PliotronX]

It's a point-to-point subnet. Typically it will be your next hop (gateway) and your router occupying the two usable addresses.

 

[lawcore]

I got

Gateway x.x.x.232
Router x.x.x.233
Spare IP x.x.x.234
Broadcast x.x.x.235


Router picks up 233.

But I am able to add 234 & 232 as WAN IP alias

which are also useable.

So giving me a total of 3 IP's that I can use.

 

[mv2devnull]

That does not look right.

Address:   192.168.0.232         11000000.10101000.00000000.111010 00
Netmask:   255.255.255.252 = 30  11111111.11111111.11111111.111111 00
Wildcard:  0.0.0.3               00000000.00000000.00000000.000000 11
=>
Network:   192.168.0.232/30      11000000.10101000.00000000.111010 00
Broadcast: 192.168.0.235         11000000.10101000.00000000.111010 11

HostMin:   192.168.0.233         11000000.10101000.00000000.111010 01
HostMax:   192.168.0.234         11000000.10101000.00000000.111010 10
Hosts/Net: 2

The 232 should be network and the 235 the broadcast.

You say that router "picks up" 233. From DHCP of the ISP, I presume?
The router should "pick up" a gateway too and it should be 234, the only available IP.

 

[frowertr]

What exactly are you wanting to do that you need a /30 net mask? Are you setting up P2P WAN links?

 

[Gryz]

If you configure x.x.x.233/30 on your own router, and then you are able to configure x.x.x.232 and x.x.x.234 as aliases on the same interface as where you already have x.x.x.233, then that is a bug in the software (firmware) of your router.

Can you ping those interfaces ? From somewhere on the Internet (not from inside your own home-network).

Another option could be that your interface is not really a /30. Your ISP might have told you so, but on their end they might configure it as a /24 (or even shorter prefix). That would mean they can have multiple customers on the same interface. They can reach them all. But those customers can not reach each other. (Unless they also configure their interface as a /24 or whatever. And even then the layer-2 technology might not allow you to reach your neighbors).

Misconfiguration can sometimes do weird things. And some customers do weird and unsupported stuff sometimes. Just because it does something weird they actually like. Unless you have their configs, and know their intentions, it might be impossible to figure out what is going exactly.

 

[lawcore]

More information.

This is what the ISP supplied. when I requested a IP block 4

Gateway .232
Router .233
Spare IP .234
Broadcast .235

How it is setup in the router.

Router picks up .233 as main IP.

.232 & .234

can both be pinged externally. I even did a test and swapped about port 80 between IP's to check you can access the same webpage from a external source.

From my understanding.

.233 is the IP the router should pick up from the ISP.
.234 is the spare IP I can use for web server/exchange etc etc.

Hence as advertised by the ISP you only get 2 useable IP's. Well they techically say one.

I've also been reading the gatway IP can be used but it's not advisable to to be unstable & like you mentioned above possible it's shared!

 

[Gryz]

Gateway .232
Router .233
Spare IP .234
Broadcast .235

This is a bunch of meaningless dribble.
It has no information at all.
Your ISP is clueless.

First of all, a gateway is a router. In the 80s, Internet people referred to routers as gateways. Somewhere in the early 90s everybody started using the word router. Only the term "default gateway" remains. The "default gateway" is a router. But "default gateway" is only used by endstations (PCs, servers, laptops, phones). A router will never use a "default gateway".

So the words "router" and "gateway" are meaningless in that list.

Second thing is: on the subnet we're talking about, there are 2 routers. The ISP's router that is part of their backbone. (Or access/distribution layer, to be precise. These are called B-RAS or BNG routers). So saying "the router's IP address is this" is meaningless. There are 2 routers involved. Which one are they talking about.


BTW, BNG stands for Broadband Network Gateway. But that terminology is used by ISPs and telcos only. Not by endusers.

So maybe they mean:
Gateway .232 -> the ISP's router
Router .233 -> your router
Spare IP .234 -> what??
Broadcast .235 -> correct

The only thing they got correct is the broadcast address.
But what is a "spare IP" ? There are no spare IP-addresses on a /30. As other have said here, a /30 has 4 IP addresses. The first one is the "network address". The last one is the broadcast-address. The middle 2 addresses can be assigned to boxes. In your case: one ip-address for your ISP's router, and one ip-address for your own home-router.

How it is setup in the router.
Router picks up .233 as main IP.

Did you configure this manually ?
Was this already configured by the ISP manually when you received your router ?
Or (most likely) did your router pick up .233 via PPP (when you have ADSL) or DHCP (when you have cable or fibre) ?

.232 & .234 can both be pinged externally.

That's unusual that you can ping .232. That should not be possible.
Your router must be weird.
Can you tell us what brand/type/os-version it has ?

That you can ping .234 is normal. If .233 is your ip-address, then .234 must be the ip-address of the ISP's router connecting to your router. Normally you can ping that one too.

Sometimes you can ping the broadcast-address. In your case the .235 address. It just means that all devices on that network will respond to the ping request. On a /32 you can have 2 devices, so a ping to .235 could yield to ping-replies.

I even did a test and swapped about port 80 between IP's to check you can access the same webpage from a external source.

From my understanding.

.233 is the IP the router should pick up from the ISP.
.234 is the spare IP I can use for web server/exchange etc etc.

Hence as advertised by the ISP you only get 2 useable IP's. Well they techically say one.

I've also been reading the gatway IP can be used but it's not advisable to to be unstable & like you mentioned above possible it's shared!

If you get a /30, you get 2 ip-addresses. One used by your ISP and one used/usable by you. There is no other way. There are no extra ip-addresses. Unless your ISP does something funky. In that case, just ask them. If you keep guessing, you will never really understand what is going on.

Do you really need a 2nd IP-address on your router's interface to your ISP ? I don't see the point.

 

[lawcore]

This is a bunch of meaningless dribble.
It has no information at all.
Your ISP is clueless.

First of all, a gateway is a router. In the 80s, Internet people referred to routers as gateways. Somewhere in the early 90s everybody started using the word router. Only the term "default gateway" remains. The "default gateway" is a router. But "default gateway" is only used by endstations (PCs, servers, laptops, phones). A router will never use a "default gateway".

So the words "router" and "gateway" are meaningless in that list.

Second thing is: on the subnet we're talking about, there are 2 routers. The ISP's router that is part of their backbone. (Or access/distribution layer, to be precise. These are called B-RAS or BNG routers). So saying "the router's IP address is this" is meaningless. There are 2 routers involved. Which one are they talking about.


BTW, BNG stands for Broadband Network Gateway. But that terminology is used by ISPs and telcos only. Not by endusers.

So maybe they mean:
Gateway .232 -> the ISP's router
Router .233 -> your router
Spare IP .234 -> what??
Broadcast .235 -> correct

The only thing they got correct is the broadcast address.
But what is a "spare IP" ? There are no spare IP-addresses on a /30. As other have said here, a /30 has 4 IP addresses. The first one is the "network address". The last one is the broadcast-address. The middle 2 addresses can be assigned to boxes. In your case: one ip-address for your ISP's router, and one ip-address for your own home-router.

Did you configure this manually ?
Was this already configured by the ISP manually when you received your router ?
Or (most likely) did your router pick up .233 via PPP (when you have ADSL) or DHCP (when you have cable or fibre) ?

I configured it manually but its set to DHCP. Would it be adviseable to set it to static and select one of the IP's

That's unusual that you can ping .232. That should not be possible.
Your router must be weird.
Can you tell us what brand/type/os-version it has ?

It's a Draytek 2920n Firmware Version : 3.6.8.4


That you can ping .234 is normal. If .233 is your ip-address, then .234 must be the ip-address of the ISP's router connecting to your router. Normally you can ping that one too.

Sometimes you can ping the broadcast-address. In your case the .235 address. It just means that all devices on that network will respond to the ping request. On a /32 you can have 2 devices, so a ping to .235 could yield to ping-replies.

If you get a /30, you get 2 ip-addresses. One used by your ISP and one used/usable by you. There is no other way. There are no extra ip-addresses. Unless your ISP does something funky. In that case, just ask them. If you keep guessing, you will never really understand what is going on.

Do you really need a 2nd IP-address on your router's interface to your ISP ? I don't see the point.

Thanks for the well informed reply.

This is copied straight from plus net's website.

4 IP Block /30

A 4 IP block provides 2 usable IP addresses (1 for the router and 1 for servers, PC, etc.)
The customer must justify why they need an additional 1 static IP address
No RIPE form is required for a 4 IP block and this can be authorised by our Customer Support Team


.233 picked up viv DHCP on the router from the ISP.
.234 is my additional IP


(.232 I also added as a additional IP)

Reason I need 2 is due to onsite spam filter gateway for exchange we use & 2x ssl certs for a web application that works with our accounting software..




Either way it works. But Just thought I ask the question. As I techically have use of 3 IP's and can direct them to different onsite servers and from a external souce it goes to the correct location.

Which effectively has given me useabilty of 3 IP's