Group of hosts with a common set of requirements connected as if on the same broadcast domain despite physical location

learn more… | top users | synonyms

78
votes
2answers
80k views

How do VLANs work?

What are VLANs? What problems do they solve? I'm helping a friend learn basic networking, as he's just become the sole sysadmin at a small company. I've been pointing him at various questions/answers ...
51
votes
7answers
72k views

OpenVPN vs. IPSec - Pros and Cons, what to use?

Interestingly I have not found any good search results when searching for "OpenVPN vs IPSec". So here my question: I need to setup a private LAN over an untrusted network. And as far as I know, both ...
25
votes
3answers
10k views

What happens when a consumer switch receives a VLAN-tagged Ethernet frame?

Suppose you connect a trunk port from a VLAN capable network switch to a (VLAN incapable) consumer-grade network switch via a direct cable. Now the former switch send the later switch a 802.1Q-tagged ...
23
votes
4answers
13k views

Why do people tell me not to use VLANs for security?

As per title, why do people tell me not to use VLANs for security purposes? I have a network, where a have a couple of VLANS. There is a firewall between the 2 VLANs. I am using HP Procurve switches ...
18
votes
7answers
16k views

How many VLANs are too few and too many?

We're currently running a netwok of 800+ PCs and 20+ servers, the network infrastucture is along the lines of Core Switch 10Gb-> Area Switch 2GB-> Local Switch 1GB-> Desktop. All running 3Com ...
16
votes
3answers
2k views

Phones on some switches cannot complete DHCP process

Background I have a Windows DHCP server (Server 2008 R2) handing out addresses for several scopes. One of those scopes is for some Mitel IP Phones. The phones are configured to use dhcp option 125 to ...
14
votes
3answers
4k views

How can I set up VLANs in a way that won't put me at risk for VLAN hopping?

We're planning to migrate our production network from a VLAN-less configuration to a tagged VLAN (802.1q) configuration. This diagram summarizes the planned configuration: One significant detail is ...
12
votes
2answers
2k views

Encryption over gigabit carrier ethernet

My conclusion to this was to pipe VLAN trunks through EoIP tunnels and encapsulate those in hardware assisted IPSec. Two pairs of fairly inexpensive Mikrotik RB1100AHx2 routers proved capable of ...
11
votes
1answer
30k views

VLAN tags not shown in packet capture (Linux) via tcpdump

I am adding a tagged VLAN onto eth0: #ip link add link eth0 name eth0.20 type vlan id 20 This results in: #ip link 2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc ...
11
votes
2answers
31k views

Multiple VLANs, multiple subnets, single DHCP server?

At my job we are prepping to transition from multiple LANs connected over slow VPN connections to a single MAN connected over fiber, and I've got a few questions. First of all, we are planning on ...
11
votes
5answers
3k views

tc u32 — how to match L2 protocols in recent kernels?

I have a nice shaper, with hashed filtering, built at a linux bridge. In short, br0 connects external and internal physical interfaces, VLAN tagged packets are bridged "transparently" (I mean, no VLAN ...
10
votes
4answers
37k views

Best way to segment traffic, VLAN or subnet?

We have a medium-sized network of around 200 nodes and are currently in the process of replacing old daisy-chained switches with stack-able or chassis style switches. Right now, our network is broken ...
10
votes
1answer
11k views

Connect to multiple AP with one Wifi adapter under Linux/FreeBSD?

How can I connect to more than one Wifi access point simultaneously using a single wireless adapter? I'm currently using pfSense as my home router and I want it to connect to multiple APs wirelessly. ...
10
votes
7answers
3k views

Are VLANs necessary for my environment?

I'm the new network manager for a school. I've inherited an environment made up of several Windows servers, about 100 Windows clients, 10 printers, 1 Cisco router, 6 Cisco switches, and 1 HP switch. ...
9
votes
1answer
2k views

How can I setup vSphere so that VLAN tags are not stripped at the vSwitch?

I am trying to test a VLAN-related networking issue, so I thought that firing up a couple virtual machines would be the easiest and cleanest method to test the problem. On the vSphere server I ...
9
votes
3answers
5k views

Cisco and Linux and Vlans

I appear to have some fundamental misunderstanding of how VLANs work on Linux, and I'm hoping the good people here can educate me. Cast: One Cisco 3560, one VLAN, and one Linux box [1]. Cisco -----...
8
votes
5answers
13k views

Is it possible to connect a single NIC to two different VLANs?

I know it is possible to assign multiple IP addresses to the same NIC as long as they are on the same sub-net (e.g. server A can be assigned both 192.168.1.1 and 192.168.1.2). However, is it possible ...
8
votes
3answers
2k views

VLAN's - Planning?

Our network is a flat L2. At some point we need to (I want to, but it's not strictly my responsibility) start to VLAN it down as we're obviously going to have a lot of broadcast chatter going on, and ...
8
votes
1answer
735 views

Are VLan's used to split my switch into segments?

I'm trying to plan for the following Small Office network setup: 3x Internet connections Things connected to the port in each colour can only get routed through their corresponding internet port. ...
8
votes
4answers
10k views

Can't communicate between lan ports on openwrt router

I've got a WBMR-HP-G300H Buffalo Airstation router on which I've installed the lates OpenWRT software. All is working well (ADSL, WIFI etc) except for one niggle. I can't communicate between lan ...
8
votes
4answers
3k views

New network design from a noob. VLANS, IP's, hardware, etc. Any comments please

I’m currently planning a large network infrastructure for a University in Ethiopia and would like people’s comments on my planning. Please bear in mind I have never done networking before. The campus ...
8
votes
1answer
899 views

kvm, vlans, how to simulate a 'mirror' port

I'm working with kvm 0.14.1 on an ubuntu lucid x64 box. I've got 3 vlans configured, one that is a bridge to the host's eth1. The others are host only. I want to start playing with snort. Is there ...
8
votes
1answer
585 views

Does setting MTU on logical interfaces affect physical interfaces

I've been using a combination of interface bond-, vlan- and bridge-interfaces to provide redundancy and different logical network layers to xen domU's. This setup is working well however i'm a bit ...
8
votes
3answers
16k views

OpenWrt Configuring Tagged and Untagged VLAN on the Same Port

I have installed OpenWrt on a MikroTik Routerboard RB750UP (AR7240 CPU with AR9330 built in switch). I have included additional details below, but my question is: How do I configure an untagged and ...
8
votes
2answers
3k views

HP Procurve Issue Passing Multiple VLANs over a link

Just to start off with I am a Cisco guy that got placed into an HP project. Basic topology overview from outside in: ASA 5505 with two Ethernet connections to a 2610 switch. This switch is then ...
7
votes
2answers
2k views

How to set up VLAN network

I'm changing my network from having every device on flat network to using VLans. My problem is that we already have a lot of devices on this network(192.168.20.0/24). From theory, I read that each ...
7
votes
7answers
49k views

Why does a VLAN have an IP address?

A dumb question for the majority, but I am interested to know "why does a VLAN have an IP address?" Is this address different from the default gateway? Or is this address, same as broadcast address ...
7
votes
2answers
1k views

Architecting your network when you run out of VLANs

This is an entirely hypothetical question, I'm not in this situation now. What happens to your VLAN topology and routing if you run a multi tenant network and you have more than 4096 customers? Do ...
7
votes
3answers
22k views

What do switches do to tagged and untagged VLAN packets?

Let's say we have a 4-port switch that is VLAN capable. 1 2 3 4 Port 1 is TAGGED to VLAN10` and `UNTAGGED to Default_VLAN(1) Port 2 is UNTAGGED to VLAN10 Port 3 is UNTAGGED to ...
7
votes
9answers
3k views

Need prosumer router/firewall/vpn/vlan/nat advice [closed]

Looking for a recommendation on a device (or devices I guess) to do router/firewall/vpn/vlan/nat functons for my home network. Right now, I'm doing this with an IPCop box, but I'd prefer a little ...
7
votes
2answers
179 views

VLAN Inheritance?

Imagine the following scenario: Primary Switch | (VLAN 3 Port) | Unmanaged Switch (Dedicated to IPMI Interfaces) | / \ / \ Server 1 ...
7
votes
1answer
636 views

Switches - Do I need Spanning Tree?

If I have two switches connected to one another by a fibre link, and each of those switches is also connected into a local switch, and those two local switches are linked, I'm correct in thinking that ...
7
votes
1answer
4k views

Send trunk directly to vm in HyperV 2012

I'm setting up OpenBSD as a VM in HyperV 2012. It would be easier for me to just create one interface on the vm and have OpenBSD take care of setting up the vlans. Is it possible to tell HyperV to ...
7
votes
2answers
8k views

tcpdump: capture one of several vlans

I want tcpdump to capture VLAN 1000 or VLAN 501. man pcap-filter says: The vlan [vlan_id] expression may be used more than once, to filter on VLAN hierarchies. Each use of that expression ...
7
votes
2answers
5k views

VLAN for WiFi traffic separation (new to VLANing)

I run a school network with switches in different departments. All is routed through to a central switch to access the servers. I would like to install WiFi access points in the different departments ...
7
votes
3answers
1k views

Linux NIC bonding on top of vlan interfaces?

Is it possible to set up bonding(active/backup) on top of existing vlan interfaces ? Assume the following scenario: Linux Server with 2 NICs connected to separate switches iSCSI initiator + MPIO to ...
7
votes
1answer
3k views

How to configure a HP Procurve network for IPv4+IPv6

The setup: We are an apartment complex with approximately 1700 units. Every apartment has internet with an ethernet plug in each. The network has 60 HP 2910al-48G switches connected to a central HP ...
7
votes
2answers
1k views

Linux Router Problem

I have a Linux based router with four interfaces (each with its own private subnet). When I directly connect a device directly (i.e. no switch, just a patch cable) to one interface and another device ...
6
votes
3answers
28k views

Duplicate MAC address on the same LAN possible?

Let's say someone is on the same network as me and spoofs their MAC address to match mine: Is this possible? Can two or more clients with the same MAC address be on the same network at the same time ...
6
votes
4answers
3k views

Best Approach for subnetting/VLANing traffic?

Our network is currently setup with no subnets or VLANs. We are looking at going to VoIP so this needs to change before VoIP is installed. I believe that we want to use VLANs to separate Voice and ...
6
votes
1answer
1k views

Designing segmented LAN with fairly shared hi-speed internet access on a tight budget

With another member of the owners' association, I've been tasked with designing and setting up shared, hi-speed, internet access, for our apartment building. We have very little budget and hope to be ...
6
votes
1answer
1k views

Looking for a tool to plan network/vlan topologies [closed]

I'm looking for a tool (desktop or web-based) that we can use to plan our network topologies using VLAN's. Something capable of defining switches, and mapping VLAN's to the ports and allowing use to ...
5
votes
8answers
3k views

Is there a good way to programmatically configure VLANs on a managed switch?

My situation is that my company makes a product that (currently) requires the user to set up a dozen or so VLANs on a managed switch that is dedicated to the exclusive use with our product. Currently,...
5
votes
3answers
942 views

Campus VLAN Segmentation - By OS?

We've been thinking through re-arranging our network and VLAN configuration. Here's the situation. We already have our servers, VoIP phones, and printers on their own VLANs, but our problem lies with ...
5
votes
5answers
2k views

Mixing SAN iSCSI Traffic with core network traffic, Am I asking for trouble?

I am configuring a new network and had a couple questions I am finding hard to find good answers about best practices on using VLANs to separate Core network traffic and iSCSI traffic. The switches ...
5
votes
2answers
2k views

Multiple vlan issue with procurve switch

I have a cisco asa5505 as my rtr/fw(10.1.3.254). I have vlan 1 and vlan 3. Vlan 1 is my default all access vlan. Vlan 3 is my Guest(dmz) vlan. I can't seem to get a dhcp ip address when my laptop ...
5
votes
3answers
944 views

Design Critique Needed ( VLAN & ESXi )

So this is my new "project" which consists of tearing down our legacy network and re-doing it correctly. As of now it is a mess. Production is a hogpoge of legacy servers that should have been put to ...
5
votes
1answer
257 views

In what scenarios would a VLAN not align 1:1 with a subnet?

Under what scenarios would a VLAN not align with a subnet. I've been told that genearlly they always go 1 to 1. What are some examples or scenarios, and reasons for anything besides that, and for what ...
5
votes
2answers
233 views

Hyper-V Virtual Switches and DHCP

What is the best way to force VLAN segregation accross multiple Virtual switches? I have probably a rather complex setup going in the effort to get essentially 4 separate virtual switches. The ...
5
votes
2answers
6k views

DHCP Server with multiple scopes. Which one does it use to handout an IP?

I have 4 DHCP Scopes. 10.200.0.0 <--------DHCP Server Lives Here 10.54.0.0 10.16.0.0 10.32.0.0 A DHCP broadcast request is sent to my DHCP server. How does it decide which scope to pull an ...