dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
892
share rss forum feed


marvelto

@start.ca

[Cable] Multiple IPs

I've noticed that if I hook my cable modem up to a network switch and connect both my gateway and my VOIP box they each get a public IP. This seems to be the best approach for me* but is this a legit approach? Is there a limit to the number of IPs I can use?

* (since putting the VOIP box behind the gateway is sketchy at best, and having the VOIP box in front of the gateway kills the throughput)

Cloneman

join:2002-08-29
Montreal
kudos:4
Reviews:
·TekSavvy DSL
·Bell Fibe
I don't know how many public IPs your ISP allows you to have.. often, its not more than 2 with most Cable ISPs afaik...

Most people are successful at running their VoIP behind the NAT. There seems to be a lot of confusion regarding keep-alive and port forwarding and that sort of thing though, so you are correct in assume public IP is the most straightforward solution...

Fraoch

join:2003-08-01
Cambridge, ON
kudos:2
Reviews:
·TekSavvy Cable
reply to marvelto
My DCM476 seems to allow this:

Configuration Parameters:
Computers Allowed by Service Provider: 2
Computers Detected by Modem: 1
 

Whether TekSavvy does is up to them but the modem seems technically capable.

--
TekSavvy 28/1 cable - Technicolor DCM476 - Ubiquiti EdgeRouter Lite - Amer Networks SGD8 switch - ASUS RT-N66U (as WAP)


TypeS

join:2012-12-17
London, ON
kudos:1
reply to marvelto
Better to have the VoIP box behind a router if you ever need to implement QoS to ensure your VoIP service always has enough bandwidth to operate.


d4m1r

join:2011-08-25
reply to marvelto
On the Rogers cable network, it is possible to get 2 public IPs.


TwiztedZero
Nine Zero Burp Nine Six
Premium
join:2011-03-31
Toronto, ON
kudos:5

1 edit
reply to marvelto
This snip from my SB6120 might give you a little idea about the limits on your side of the Cable Modem - supposing you're using a switch.
---



I'm going to assume as long as you can route up to that many on your side (Intranet LAN) you're good. The modem itself will still only get 2 IP's no matter your topology.

If I'm somehow wrong - Hey, edumacate me
This old dog can still learn new stuff.
As for the VoIP stuff, colour me 'tarded 'coz Deafies don't Use fones as much.
--
----|- From the mind located in the shadows of infinity -|----
Nine.Zero.Burp.Nine.Six
Twitter = @TwiztedZero
Chat = irc.teksavvy.ca

Fraoch

join:2003-08-01
Cambridge, ON
kudos:2
Reviews:
·TekSavvy Cable
said by TwiztedZero:

I'm going to assume as long as you can route up to that many on your side (Intranet LAN) you're good.

Interesting, how can upstream equipment tell how many LAN clients you have? I don't think MAC addresses can get past your internal LAN router - won't upstream equipment just see the modem's MAC?

Or is this the modem's built-in router than only has a DHCP pool size of 32 clients? This shouldn't be an issue if it's bridged, right?
--
TekSavvy 28/1 cable - Technicolor DCM476 - Ubiquiti EdgeRouter Lite - Amer Networks SGD8 switch - ASUS RT-N66U (as WAP)


TwiztedZero
Nine Zero Burp Nine Six
Premium
join:2011-03-31
Toronto, ON
kudos:5
Typical Residental Topology:
•Everything on the switch (subnet) gets routed to the main router (1IP).
•Back at the modem there is still 1IP available for say, direct pc to modem trouble shooting.



•Where LAN switch = up to 32 PC's theoretical.

Keep in mind a switched network can only handle so many simultaneous connections at a time (generally up to 4000).

Typical home network switches usually come with 5 to 8 ports anyways. (Most of these types are dumb switches)

You can of course buy industrial smart switches with 24 ports etc... at substantial cost. Most people don't need that much in their homes.

And we're not even talking VLan's in this instance, which is another slightly different topology.

Smallnetbuilder for more.
--
----|- From the mind located in the shadows of infinity -|----
Nine.Zero.Burp.Nine.Six
Twitter = @TwiztedZero
Chat = irc.teksavvy.ca

einto

join:2011-06-10
Toronto, ON

1 edit
said by TwiztedZero:

Typical Residental Topology:
•Everything on the switch (subnet) gets routed to the main router

But this setup looks like a case where you are using NAT behind the modem (likely with the modem), the configuration the OP was referring too was likely

INTERNET
|
+CABLE_MODEM (GATEWAY DISABLED)
  |
  + SWITCH
     |
     + VOIP Box (Internet IP1 - 206.248.x.x)  --> Phone lines
     |
     + GATEWAY (Internet IP2 - 206.248.x.y)
        |
        + HOME_PC1 (LAN IP - 192.168.0.100)
        |
        + HOME_PC2 (LAN IP - 192.168.0.101)
        |
        + HOME_PC3 (LAN IP - 192.168.0.102)
 


TwiztedZero
Nine Zero Burp Nine Six
Premium
join:2011-03-31
Toronto, ON
kudos:5
Yup thats the idea

Fraoch

join:2003-08-01
Cambridge, ON
kudos:2
Reviews:
·TekSavvy Cable
Actually what I meant was - what does this text in the modem mean?

Does it mean the upstream provider somehow has the ability to detect and restrict the number of LAN devices mapped to that one IP address?

Or does this simply refer to the modem operating in router mode and only having a DHCP pool size of 32?

Many years ago Rogers stated that there could be "only one computer" behind their cable modems for their light packages. I thought that was ridiculous, it doesn't increase costs on their side if I have several devices behind a router, so that's what I did and they never caught on.

I thought that behind NAT this didn't matter - the router maps all internal IPs to one external IP, presenting only the MAC of the router to the outside. It shouldn't matter how many LAN devices are behind the router - I mean you can have up to 255 per VLAN, right? What does it matter to the ISP how many devices you have behind your own router? Do they even have a way of determining this?
--
TekSavvy 28/1 cable - Technicolor DCM476 - Ubiquiti EdgeRouter Lite - Amer Networks SGD8 switch - ASUS RT-N66U (as WAP)

einto

join:2011-06-10
Toronto, ON
said by Fraoch:

I thought that behind NAT this didn't matter - the router maps all internal IPs to one external IP, presenting only the MAC of the router to the outside. It shouldn't matter how many LAN devices are behind the router - I mean you can have up to 255 per VLAN, right? What does it matter to the ISP how many devices you have behind your own router? Do they even have a way of determining this?

You are correct in this. There is no easy* way for the upstream provider to tell how many devices are behind the device doing the NAT as all internal IPs get mapped to the external IP with different ports.

*Technically it might be possible to differentiate devices behind the NAT using OS fingerprinting or other DPI techniques, but I've never heard of a provider doing that


cable4me

@teksavvy.com
reply to Fraoch
>I mean you can have up to 255 per VLAN
You can have much more devices than 255 in a subnet. i.e. it doesn't have to be a /24 if your router supports it.


TwiztedZero
Nine Zero Burp Nine Six
Premium
join:2011-03-31
Toronto, ON
kudos:5
reply to einto
Yup they don't do that anymore. They used to once upon a time years ago. You'd have to pay for your net plus each additional pc in the household. Glad those days are over.


BTC Kevin

join:2011-10-01
Nepean, ON
kudos:1

1 recommendation

reply to marvelto
it allows 2 IP's, it will allow it ok. but that said, using only one is best. having the second one free allows for a bit of leniency from the DHCP server.

I've had the router go offline temporarily before, when using my second IP for voip device. and well... Rogers wouldn't give a new IP.

Example1, Sometimes the MAC-IP relationship messes up. Having the second one assignable ensures the router can make a second DHCP relationship.

Example2, if your router connected has issues. and you unplug it and plug in a laptop to test. the laptop binds to IP#2. When both addresses have been bound to the MACs of the router+voip devices, you would have to WAIT. Eventually the DHCP will decide to clear both records before you get a new one.

Secondly, address allotment pools are a concern. if all the users use 2 IP's this increases how many IP's TSI needs out on the network.

lets presume a regional area server by a DHCP pool has 1000 IP's in it. And TSI has 750 users in the area.

and lets run some theoretical numbers:

1 IP each means 750/1000 IP's in use. leaving 250 as free. with a 75% IP allotment capacity.

If out of 750 users 500 of those users was to use 2 IP's.

2 IP each means 1000/1000 IP's in use. And 250 users have fail to receive an IP. with a 100% IP allotment currently in use. and 33% of the users having a DHCP connection issues because no addresses are assignable. TSI would need 1250 IP's to assign, and a pool of 1667 IP's to maintain a 25% free margin as it was when each user had 1 IP. As you see TSI would be having to allocate 667 more IP's in this case to the server.


BTC Kevin

join:2011-10-01
Nepean, ON
kudos:1
PS. sorry if did any math wrong, but you all kinda get the picture.


TwiztedZero
Nine Zero Burp Nine Six
Premium
join:2011-03-31
Toronto, ON
kudos:5
reply to BTC Kevin
Wow yeah, and this is interesting. Thanks for the lil eye opener

*Cheers*