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Webcast-Catalyst9k
New Member

Forwarding between Vlans without introducing a router hop

Hi,

I am looking for a way to forward between 2 vlans, but remaining within a single L3 domain.

Example: PC1--RTR1--VL10--SW1--VL20--RTR2

Notes: PC1 has default gateway of RTR2

Any ideas on how to do this without adding another L3 hop?

Thanks

Alan

6 REPLIES
New Member

Re: Forwarding between Vlans without introducing a router hop

Oops sorry, forgot to mention, RTR1 has default gateway of RTR2, not PC1

Re: Forwarding between Vlans without introducing a router hop

i am not really understood about ur exact requirement. if you put it in diagram, i can give some suggestion.

New Member

Re: Forwarding between Vlans without introducing a router hop

PC1----RTR1--(VL10)--SW1--(VL20)--RTR2

PC1 must be able to ping RTR2.

PC1 Def.GW is RTR1.

RTR1 Def.GW is RTR2

SW1 must forward frames from VL10 to VL20 and vice versa.

SW1 has only L2 config, No IP addresses etc..

New Member

Re: Forwarding between Vlans without introducing a router hop

Connect pc1 to vlan 10 interface in switch, and rtr2 to vlan 20 interface in switch. Connect rtr1 to switch and configure dot1q trunk between switch and rtr1 allowing vlan 10 and?20. Configure bridging between vlan 10 and vlan 20 subinterface on router.

Forwarding between 2 vlans on same IP subnet is called bridging :o)

New Member

Re: Forwarding between Vlans without introducing a router hop

Thanks pkrohn, I hadn't considered that as RTR1 is not under my control and so cannot be configured as such. For that matter RTR2 is not under my control either. This leaves me SW1 which I can configure. Actually, bridging is not ideal as it will merge the vlans. Is there a way in SW1 to do forwarding between vlans based on ACL or the like?

New Member

Re: Forwarding between Vlans without introducing a router hop

Hi alan -

If you do routing in the switch between different vlans and IP nets you can apply an access-list to the L3 interface - but then of course you introduce a L3 hop, and will have problems with the placement of the DG.

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