2 subnets 1 switch no VLAN

Hi All,

One simple question, can I use 2 subnets on 1 switch without VLAN setup. What is the Pros and Cons? Thanks.

Reply to
wubing
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Yes, you can. It will work and the main difference is that broadcast of either network will be visible in the other one.

Regards

fw

Reply to
Frank Winkler

Thanks. But 2 subnets will not talk to each other, only broadcast. Is this will slow down the switch?

Reply to
wubing

PRO - You can still have two IP address ranges functioning on a switch without VLANs if your switch cannot use VLANs. PRO - The IP hosts in one subnet cannot directly unicast to the IP hosts in the other subnet. PRO - Your router for these subnets can use the "ip address W.X.Y.Z W.X.Y.Z secondary" command to provide a default gateway IP addres for each additional subnet on the same interface. That's right, you can have multiple secondary IP addresses.

CON - This is not why subnets were invented. These two subnets are supposed to be on different LAN segments. CON - The broadcasts from either subnet will be present in the same broadcast domain. Multicasts, if present, will be the same. CON - Your router interface throughput will be more heavily loaded. Hosts must send data into the router interface for it to be sent right back out to a host in the same LAN segment. This would still be the case if the router had a VLAN trunk to the switch, but at least more capabilities would be available.

If the destination IP address is within the sending hosts IP address range, the data is sent with the destination IP address in the IP packet and the destination MAC address in the ethernet frame.

If the destination IP address is not within the sending hosts IP address range, the data is sent with the destination IP address in the IP packet and the default gateway router MAC address in the ethernet frame. The router would then receive the frame, discard the frame to examine the IP packet inside, see the destination IP as some other IP address (as opposed to someone telnetting directly to the router for administration), re-wrap the IP packet with an ethernet frame destined to the next hop router, and forward the frame. This repeats until the last router connected to the destination host subnet sends the IP packet wrapped in an ethernet frame with the destination hosts MAC address on the frame and the destination host receives it.

=========== Scott Perry =========== >

Reply to
Scott Perry

What about two routers, two subnets and one switch?

Reply to
wubing

Huh.

And here I thought switches that can't support VLAN only worked at layer two and could only switch by MAC address.

Reply to
Brian

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