Network gurus - basic question

Hetzkes Ballet Teacher · 7th April 2011, 05:20 PM

I'm having an utter mental blank here - can someone put me out of my misery??

I know a single NIC/port can have multiple IPs assigned to it, but can they be on different subnets?

Say you've got a switch with three hosts attached, configured like this ([..]= a NIC), where Host A is also the gateway to the internet.

+---[192.168.1.1/24, 192.168.2.1/24] - Host A - [WAN IP] <----> internet
+---[192.168.1.2/24] - Host B
+---[192.168.2.2/24] - Host C

Am I right in thinking that B and C be will able to communicate with A and the internet, but not with each other (unless A is configured to route between them)?

In other news, I've also started to dribble and forget my name.

Stevie Freestein II · 7th April 2011, 05:24 PM

Modern washing machines usually only have a cold inlet hose.

If that helps?

Hauser's-Helmet · 7th April 2011, 05:35 PM

TiredEyes · 7th April 2011, 05:52 PM

I think the router would need sub-interfaces configured on it to allow cross VLAN? communication, so yes - but I'm no guru* !!

*because I didn't know you could assign 2 IP addresses to one NIC

Hetzkes Ballet Teacher · 7th April 2011, 05:58 PM

Quote:

Originally Posted by TiredEyes

I think the router would need sub-interfaces configured on it to allow cross VLAN? communication, so yes - but I'm no guru* !!

*because I didn't know you could assign 2 IP addresses to one NIC

Nee VLANs here, just regular LAN.

It's quite common to have multiple IPs on a single NIC. For example you might have one physical server on your intranet, that serves multiple internal web sites. You can do that by making it look like it's at several IP addresses on the same subnet, one for each web site (news.server.local, porn.server.local, etc). Though of course that's not the only way - you could use one IP but different page names, ports, etc.

Quote:

Originally Posted by Hauser's-Helmet

Yes.

Is that an authoritative yes, a talking shite yes, or an authoritative but talking shite yes?

Hetzkes Ballet Teacher · 25th April 2011, 06:27 AM

Turned out it was possible. You can have any number of subnets on one physical segment that you like, as long as you assign the router's connection (to that segment) an IP in each of them, to be the default gateway for each. The router will route between them just like it would if they were on different physical segments.

When the router is a WS2008 box, that's not a problem, you just used the "Advanced" button on the TCP/IP options dialog box, and hoy the IPs in there.

If you're using its DHCP server, you also have to create a scope for each of the subnets as normal, but you then have to put them inside a superscope for the segment.

You learns summat every day on the SMB!

Flared Hicks · 25th April 2011, 10:31 AM

Yeah, I do this all the time in network courses where they don't have a dedicated router. Windows Server from NT onwards has had the ability to act as an IP router.

Hetzkes Ballet Teacher · 25th April 2011, 10:51 AM

Quote:

Originally Posted by Flared Hicks

Yeah, I do this all the time in network courses where they don't have a dedicated router. Windows Server from NT onwards has had the ability to act as an IP router.

All versions of Windows can, even clients since 2000. The point here was having multiple subnets on a single segment though, and I couldn't get a straight answer anywhere about it! So I just tried it and for once it worked.

I probably should have used VLANs, but that sounds like a bigger can of worms.

Spug · 25th April 2011, 10:58 AM

Quote:

Originally Posted by Hetzkes Ballet Teacher

All versions of Windows can, even clients since 2000. The point here was having multiple subnets on a single segment though, and I couldn't get a straight answer anywhere about it! So I just tried it and for once it worked.

I probably should have used VLANs, but that sounds like a bigger can of worms.

wrong.

Flared Hicks · 25th April 2011, 11:01 AM

Quote:

Originally Posted by Hetzkes Ballet Teacher

All versions of Windows can, even clients since 2000. The point here was having multiple subnets on a single segment though, and I couldn't get a straight answer anywhere about it! So I just tried it and for once it worked.

I probably should have used VLANs, but that sounds like a bigger can of worms.

yeah what I should have said is that I often run 2 subnets off a single NIC and route between them. Handy when you're running a network analyzer as they can see all the packets when trying to see why some are ignored whilst others picked up when reading either MAC or IP headers.