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Posted by on May 7, 2008, 11:23 pm
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Hello...we tried to setup a lab by cascade the switches with multiple
VLANs, for example, that says:
1) the router has: VLAN1 and VLAN2,
2) switch1: VLAN1(1-12 port), VLAN2 (13-24 port)
3) switch2: VLAN1(1-8 port), VLAN2(9-16 port)
4) all the ports in VLAN1 are in the same subnet, same as VLAN2.
5) the router- switch1-switch2 are cascaded.
Question is that:
*when setup VLAN1/2 in switch 1/2, do we need to assign IP address/
gateway in each switch's VLAN, or it is good enough to set the iP in
router's VLAN only?
*do the VLAN name has to be the same in order to be in the same
subnet?
Thanks,
Yvette.
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Posted by Trendkill on May 8, 2008, 7:19 am
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On May 7, 11:23 pm, yvette...@gmail.com wrote:
> Hello...we tried to setup a lab by cascade the switches with multiple
> VLANs, for example, that says:
> 1) the router has: VLAN1 and VLAN2,
> 2) switch1: VLAN1(1-12 port), VLAN2 (13-24 port)
> 3) switch2: VLAN1(1-8 port), VLAN2(9-16 port)
> 4) all the ports in VLAN1 are in the same subnet, same as VLAN2.
> 5) the router- switch1-switch2 are cascaded.
>
> Question is that:
> *when setup VLAN1/2 in switch 1/2, do we need to assign IP address/
> gateway in each switch's VLAN, or it is good enough to set the iP in
> router's VLAN only?
> *do the VLAN name has to be the same in order to be in the same
> subnet?
>
> Thanks,
> Yvette.
The answer to your question depends on whether you are using a router
or a l3 switch. In your case, where you are using a router, the
router must have an interface in each vlan, and a connection to the
first switch in each vlan (either two separate connections, or a
trunk). The first switch then also must have a connection in each
vlan to switch 2 (either trunk, or two separate connections again).
The switches should be IP'ed in either vlan 1 or 2 for management, but
that interface and subsequent default gateway have NOTHING to do with
ports in those vlans and traffic routed to/from them. The router will
manage everything by arping for the MAC of the destination IP, which
the switches will flood, and then a reply will come, at which time the
router will pass the traffic to the switches for delivery by layer 2
mac only.
If however you were running a L3 switch, where a switch or pair of
switches has IPs in each vlan, and subsequently acts as the default
gateway for those vlans, then the router is just for things going
further into the network. A switch (or pair if using HSRP) would have
a physical IP in each vlan, one virtual if you were using HSRP, and
the nodes on vlans 1 and 2 would be using the switches as the default
gateways for each respective network.
Lastly, most L2 switches only allow one interface to be setup with an
IP, which is to be used for mgmt of the switch and nothing else. You
get to pick which vlan that is in. If its a layer 3 switch, you CAN
set an IP in each vlan, but this is not wise as it just causes
additional complexity and loss of addresses if you are using a router
as the layer 3 owner of the network.
However, and one last thing, if your switches are layer 3 capable, it
is a smart design choice to move layer 3 ownership of those networks
to the switches to reduce bottlenecks. As it stands right now, a
client on vlan 2 on switch 2 that needs to talk to a node on vlan 1 on
switch two, must hop to switch one, then to the router, then back to
switch 1, then back to switch 2. This effectively sets up bottlenecks
at two points as traffic is scaled. I would at least move vlan
ownership to switch 1 to reduce traffic to the router (and reserve it
only for traffic leaving the switches for another destination), or
consider moving vlan 3 and 4 to switch 2, and 1 and 2 to switch 1.
This would then make sure traffic between nodes on the same switch is
not leaving the switch.
Obviously it all depends on your design, equipment, and budget, but
daisy-chaining switches is never a good design. Since this is a lab,
who really cares, but just wanted to make that clear.
Hope this answers your question.
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