Layer 2 switch connectivity

Answered Question
Mar 24th, 2010

Friends,


I have some doubt on a current setup as below:

we have a router connected to wan link. Local interface is connected to a 3750 which is doing a layer 2 functionality & doesnt support routing protocols based on its current IOS. It has only one vlan ( vlan 20 - 192.168.103.201 /23)

Routers wan - serial wan ip
routers Lan - 192.168.102.254 /23

Switch port fa1/0/24  connected to router lan port and configured on vlan 20


there are other switches connected in this location with all of them having defalt gateway set to
routers lan ip.

Now, another router (say router2) will be introduced to this location.the intent is to connect both these
routers to 2 ports on the this switch and run glbp on the routers.
the switch would then point to this glbp.
My query is whether i can use another port on this switch on vlan 8 and connect it directly to router2
lan interface? or is that to have two connections from each router to this same switch , there needs a
change in the config?
We do not want to change anything on the switch part so that users/other devices connected will not have
to make changes on their end.

Appreciate all your help!
Thanks.

I have this problem too.
0 votes
Correct Answer by Jon Marshall about 6 years 8 months ago

My query is whether i can use another port on this switch on vlan 8 and connect it directly to router2
lan interface? or is that to have two connections from each router to this same switch , there needs a
change in the config?

If the 3750 is simply L2 then you can just connect the 2nd router to the switch to a port in the same vlan as the LAN interface of the first router and there should be no further config needed on the switch.

Jon

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Correct Answer
Jon Marshall Wed, 03/24/2010 - 18:37

My query is whether i can use another port on this switch on vlan 8 and connect it directly to router2
lan interface? or is that to have two connections from each router to this same switch , there needs a
change in the config?

If the 3750 is simply L2 then you can just connect the 2nd router to the switch to a port in the same vlan as the LAN interface of the first router and there should be no further config needed on the switch.

Jon

Cisco are currently donating money to the Haiti earthquake appeal for every rating so please consider rating all posts.

suthomas1 Wed, 03/24/2010 - 18:40

Thank You So much, another question( may be naive )... currently ip routing is not enabled on the switch.
will enabling ip routing and put a default route instead of current use of ip default gateway cause any issues or change the behaviour or mandate any further change in the setup.

Thanks.

Leo Laohoo Wed, 03/24/2010 - 18:46

The IP default gateway on a Layer 2 appliance is mostly for administration purposes only.

Ganesh Hariharan Thu, 03/25/2010 - 02:48

Thank You So much, another question( may be naive )... currently ip routing is not enabled on the switch.
will enabling ip routing and put a default route instead of current use of ip default gateway cause any issues or change the behaviour or mandate any further change in the setup.

Thanks.

Hi,

The ip default-gateway command  should only be used when ip routing is disabled on the Cisco router.

Devices within a VLAN can communicate with       each other without the need for routing. Devices in separate VLANs require a       routing device to communicate with one another so when you enabled ip routing in L3 switches.Switches receives a packet, determines that the packet belongs to       another VLAN, and sends the packet to the appropriate port on the other VLAN.

Hope to Help !!

Ganesh.H

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