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

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45
votes
2answers
27k 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 ...
12
votes
7answers
10k 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 ...
20
votes
4answers
10k 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 ...
3
votes
2answers
2k views

How do I dynamically obtain IP addresses for VLAN interfaces?

I have an Ubuntu machine on which I have created four VLANs, namely eth0.100 ,eth0.200 , eth0.300 and eth0.400. I want to dynamically obtain the IP addresses using the DHCP server. It should provide ...
2
votes
1answer
141 views

Persistent Network Configuration using KVM and libvirt

Our environment will have a KVM host setup dynamically using kickstart (easy enough). The hard part is dealing with network configuration and keeping VLAN configuration (and possibly bridge/host ...
10
votes
4answers
20k 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 ...
9
votes
4answers
2k 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
2answers
14k 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 ...
7
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 ...
4
votes
3answers
9k views

Set 802.1Q tagged port on VLAN1 on Dell PowerConnect switch

I'm having big troubles when adding this Dell switch to my network. Here we use several VLANs to segment traffic. All switches (3com and DLink mostly) have configured the same VLANs, most ports are ...
3
votes
1answer
2k 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 ...
3
votes
2answers
2k views

Debian: Should I add vlan interface into bridge for KVM?

I am setting up a Debian Squeeze box as a KVM host. I want to add multiple interfaces to each KVM guest so I want them to be on different VLANs. After reading about this, I believe the best method is ...
2
votes
1answer
3k views

How do I setup routing for two companies with different Internet connections on the same LAN?

Here's the setup: Two companies (A & B) share office space and a LAN. A 2nd ISP is brought in and company A wants its own Internet connection (ISP A) and company B wants its own Internet ...
5
votes
3answers
763 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 ...
1
vote
0answers
352 views

Ghost “vlan 0” tags added to ethernet frames in CentOS guest under OpenStack

I'm trying to debug an issue involving a KVM virtual machine instance where the instance doesn't respond to network requests when the source is on another physical machine, which is on the same subnet ...
0
votes
1answer
159 views

Cisco 877 ISR - Joining to another local network

At a remote site I have a Cisco 877 ISR providing network services (DHCP, DNS, internet, VPN back to base). I need to connect it to another companies LAN at the remote site to allow uses to print on ...
3
votes
1answer
1k views

For VLANs: difference between untagged and non-member setting for ports?

The "default" VLAN is VLAN 1, and traffic over ports are Untagged by default (at least, in the switches that we use). We've created VLAN 2 and marked the necessary ports as Tagged, and it's working ...
2
votes
3answers
5k views

DHCP server for multilple VLANs [duplicate]

Possible Duplicate: Can I have multiple DHCP servers on one network? This is a very old question i guess.In this forum itself it has been answered in Multiple VLANs, multiple subnets, ...
2
votes
1answer
377 views

Managed switch port-based DHCP allocation - general case?

I saw a strange comment bagging IT departments (i.e. sysadmins) on Slashdot the other day: half the time they cant even do a simple thing like provide a jack with a set IP address for us Reading ...
2
votes
1answer
4k views

Multiple Vlans per NIC on Windows 2008

How do I have multiple vlans (tagged) go over one NIC in server 2008 R2? I know it's possible in *nix and I know how to do that on the network side. But it doesn't help if the server 2008 R2 can't ...
1
vote
1answer
188 views

Cross-VLAN sharing and auto-discovery of selective resources

I have a network with several VLANs that each contain resources or clients with different access rights. For simplicity, let's say I have 3 VLANs: ID 10: Contains privileged clients and private ...
1
vote
1answer
494 views

How to share multicast traffic to many vlans

I have linux computer , this computer connected with entire my network via zyxel gs-2200. In this zyxel also connected router with 500 vlans, one by client. On linux computer i have vlc program ...
0
votes
2answers
569 views

Switch sending DHCP packets to wrong VLAN

I have a basic remote site with a Cisco Catalyst 2924XL switch. There are 2 VLAN's at the site: 1 Default 2 Wireless There is a single server connected via a single ethernet cable, VLAN 1 is ...
0
votes
2answers
617 views

Enabling 8021q on a nic

I'm trying to get a vlan interface on a bonded nic (Centos 5.5) and whilst the interface has been very happily created with vconfig I'm seeing no traffic on it at all. Running tcpdump and tshark on ...