Linux Networking - VLANs & Multiple IP's

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# 1  
Linux Networking - VLANs & Multiple IP's

In a "typical" data centre environment (telco, financial services etc), would a Linux OS typically have one IP address connected to one VLAN or would it have many IPs and/or VLANs. I say "Linux OS" as I'm referring to an instance of the OS not necessarily a Host or server. Think Linux OS = VM in a virtualisation context. Its common for a server/host to have many IP's and possibly in different VLANs but would an OS (VM) within that host typically just have one IP in one VLAN?

I'm asking because of an ongoing debate with a Network team that wants different IP's and VLANs per Linux OS and have us put for example ssh onto one IP, and then server traffic (e.g. HTTP) onto another IP in order to separate traffic. Is this kind of thing common in a modern data centre or not? When would one go that approach vs just putting the OS onto the VLAN thats "most representative" of its function: E.g. web proxy in DMZ VLAN, App server in Backend VLAN etc etc.
# 2  
Lots of views but no replies. Anyone?
# 3  
Hi,

I'm currently working in a high security environment, here we have a kind of hybrid setup - where we have seperate Vlans for some functions and not for others.

By way of explanation I'll give a couple of examples.

All access to Consoles, Hypervisors, ILOM and things like management consoles are on a seperate Vlan. In addition all the SAM management is on an other Vlan and all backup on yet an other Vlan. The final segregated Vlan covers other administration functions - normally where people would want to ssh onto a server for things like Oracle administration.

However from the user interface perspective we have a large address range which is spanned onto a seperate Vlan which covers VOIP and applications access from the front end.

Regards

Dave
# 4  
Thanks Dave,

I can understand how the ILOM, SAN etc would be on different VLANs. In your case, does the VM OS itself span VLANs. E.g. if its a web server listening on port 80, would the web server IP be on one VLAN, and then an IP for SSH be on another VLAN?
# 5  
I can confirm such usage, mostly in virtualized environments.
Vlan tagging and if wanted etherchannel with vlan tagging.

It is a common practice mostly and i would recommend implementing it on any new hypervisors deployments.
# 6  
Hi,

No doubt that a physical server and hence base hypervisor would connect to multiple VLANs and do VLAN tagging (e.g. in VMWare distributed switch). E.g. vMotion on one VLAN, VMWare admin on another, iSCSI on another etc.

What I'm referring to is the actual individual VM's inside the hypervisor. How many VLANs would they be connected to?

---------- Post updated at 12:23 PM ---------- Previous update was at 12:17 PM ----------

Here is an example picture :

Image

See how each individual virtual machine is connected to only one VLAN, even though the physical host is connected to many VLANS. VM1 could connect to VLAN1, VM2 to VLAN2, VM3 to VLAN2 etc. What about a scenario where VM4 connects to VLAN 1 and VLAN2? I have never once found a picture nor seen an actual environment where a virtual machine has lines going to two different VLANs. Under what circumstances would it be necessary for a a virtual machine to go to 2 different VLANs?
# 7  
For instance, if you want make backup over dedicated network ?

In that scenario you would have one public network and one backup network in different subnets.
Cluster interconnects also, you can use seperate vlans for that, which would mean that there are now total of three separate interfaces on that virtual machine.

Hope that helps
Regards
Peasant.
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