Consequences of changing port from trunk to routed port

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Oct 8th, 2008
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What are the consequences of changing a port that is trunked to a routed port? I have a port that is trunked, and it's connected to our router (3745). Is there any benefit of changing it, or any major problems of changing it?


--John

Correct Answer by Jon Marshall about 8 years 6 months ago

John


They do 2 different things.


A trunked port allows multiple vlans to travel down it and is seen as L2. Usually if connected to a router then you would use subinterfaces to route between the vlans.


A routed port will make the link between your switch and the router a routed link. If you change it to a routed port then you need to make sure you are routing for your vlans somewhere else.


Assuming this is a follow on from previous posts your inter-vlan routing will be done on the L3 switch and then you can have a routed P2P link between the L3 switch and the router. The router will now need to know how to get to the vlans on the L3 so either add a static route on the router pointing to the IP of the routed port on the L3 switch or exchange routes between the L3 switch and the router with a dynamic routing protocol.


Jon

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Correct Answer
Jon Marshall Wed, 10/08/2008 - 09:30
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John


They do 2 different things.


A trunked port allows multiple vlans to travel down it and is seen as L2. Usually if connected to a router then you would use subinterfaces to route between the vlans.


A routed port will make the link between your switch and the router a routed link. If you change it to a routed port then you need to make sure you are routing for your vlans somewhere else.


Assuming this is a follow on from previous posts your inter-vlan routing will be done on the L3 switch and then you can have a routed P2P link between the L3 switch and the router. The router will now need to know how to get to the vlans on the L3 so either add a static route on the router pointing to the IP of the routed port on the L3 switch or exchange routes between the L3 switch and the router with a dynamic routing protocol.


Jon

John Blakley Wed, 10/08/2008 - 11:00
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Yeah, it's a follow on question. :-) I learned today that our L3 is trunked to the router, but again, the L3 switch has multiple subnets assigned to that SVI. We run BGP between the two devices. I was thinking after I get my SVIs created for each VLAN I want to have, I could remove all of the addresses on the router and SVI, and let BGP handle the routing table. I can't help but feel like we could kill BGP processes somewhere because I feel that it's a little redundant. Maybe run eigrp on the L3 switch instead of bgp, but this is way in the future. Thank you for the answer once again Jon!



John





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