VLAN Configuration, Network Address...??

mp3spy · May 2006

I am trying to understand this conceptually, maybe you can help.

A LAN segment for an area has a vlan setup on the switch. The switch has an IP address and has a VLAN associated with that switch. The subnet for that VLAN is not the same subnet for that switch. But, the VLAN for that switch has its own lan segment (subnet range) and is labeled as the network address for that subnet. So for instance

Switch 1 is 40.32.2.112
VLAN for switch: 7.232.26.32 /28
Valid Hosts for that switch are .33 to .45
I don't understand how that VLAN is setup as the network address?

pannupandit · May 2006

well elaborate ur scenario.is not clear what er u saying?however each Vlan is identified by separate network address or subnet id.As am not getting what u er saying,just give some more explanation of ur problem.

EdTheLad · May 2006

It's difficult to understand what your asking but ill give it a shot.
A switch by default will have one vlan configured Vlan1, all ports of the switch are assigned to this Vlan by default.To manage a switch remotely it needs to have an IP address so you can telnet to it and configure.This IP address will be configured on Vlan 1 i.e. this management IP address will
be accessable from all ports.
When you configure a second vlan you will assign some ports to this vlan,lets call it Vlan2.The newly assigned ports will no longer be members of Vlan1 so any devices connected to these Vlan2 ports will not be able to reach the management IP address.To fix this problem you need to assign another IP address to Vlan2.So for every vlan you have, you will assign an IP address for management purposes.
As a good design concept you should allocate a different subnets to each vlan, the management IP address should be an address within the subnet range of the vlan.This subnet is not configured on the switch but on the connecting router.The switch knows nothing about what subnet addresses are assigned to what vlan, its job is to decide which ports are allowed to communicate with each other.

mp3spy · May 2006

As far as design concept, whats the advantage of having each vlan on a different subnet and assigning each vlan an address setting aside management reasons. You can just console or telnet into the switch and manage all Vlans from there??? Second, if each VLAN has its own IP address assigned, will that be the network address for each subnet? Thirdly, all nodes on that switch, how will you determine their default gateways?? Typically I will see all respective nodes in one subnet follow the same gateway on that subnet. However, different subnets still have the same gateway (4th octet) I am assuming this is configuration is done on the Router. This may be a different chapter though. Obviously that is dependent on the logical design of the network. How does each VLAN determine it's default gateway especially if there is multiple subnets on one physical switch.

EdTheLad · May 2006

mp3spy wrote:

As far as design concept, whats the advantage of having each vlan on a different subnet and assigning each vlan an address setting aside management reasons.

The reason to assign a subnet to a specific vlan is to easy your own managability.Remember if you want to route between vlans you need a router.The router will be set up with an IP address, if you required inter vlan routing the host members of the vlan must be on the same subnet as the router.

mp3spy wrote:

You can just console or telnet into the switch and manage all Vlans from there???

Cant console in if your 100km away,you can only telnet to a switch if you assign an IP address to the vlan you are a member of.

mp3spy wrote:

Second, if each VLAN has its own IP address assigned, will that be the network address for each subnet?

No,the vlan has no IP address explicitly assigned, you assign a management IP address but the only way to use the management IP address is if it shares an IP subnet address with the attached router.So its only logical to have the management IP address,the router interface address and all hosts connected to share the same subnet. You being the admin are able to plan your network and choose which IP addresses are on which devices.If you did attach 2 hosts to a vlan that didnt share the same ip address as the other hosts and the attached router,thses hosts will be isolated to talk only to each other.

mp3spy wrote:

Thirdly, all nodes on that switch, how will you determine their default gateways?? Typically I will see all respective nodes in one subnet follow the same gateway on that subnet. However, different subnets still have the same gateway (4th octet) I am assuming this is configuration is done on the Router. This may be a different chapter though. Obviously that is dependent on the logical design of the network. How does each VLAN determine it's default gateway especially if there is multiple subnets on one physical switch.

The default gateway will be the IP address of the router attached to the switch.The router will have multiple subinterfaces configured and will be a member of all vlans.So a physical router port will have multiple IP
addresses i.e. one address from each subnet.

pannupandit · May 2006

well ed_the_right is right.if we want to route between vlans we need a router.however for doing routing between vlans we need to divide our ethernet interface into subinterfaces and on each individual interface we need to enable the intervlan routing protocol(ISL or dotq).and each subinterface in the particular vlan will have the ip-address belonging to the subnet which is configured on that particular vlan.
e.g. if we have a vlan 2 and a subnet 10.1.1.0 /24 configure and another vlan2 and subnet 10.2.2.0 /24 .let an ethernet port oF router is connected to A SWITCH. let 10-10 ports are in vlan1 and vlan2.now the port which is connected to router would be a trunk port as it will carry information for more than 1 vlans.
and ethernet port of router is divided into 2 subinterfaces.let we enable ISL protocol on it .let ip addresses assigned are 10.1.1.1 and 10.2.2.1 to each sub-interface respectively.now for the devices which are connected to those ports in vlan 1 will have GATEWAY ADDRESS 10.1.1.1 and for vlan2 ,the gateway will be 10.2.2.1 and both will communicate with each other with the hepl of router.so any device in any vlan can telnet the switch . You just need to enable routing between vlans with the help of router.thats it.

VLAN Configuration, Network Address...??

Comments