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Beginner

Vlan requirement between router and switch

When we connect LAN core to WAN via Fa0/0 then we assign Vlan to Fa0/0 of Lan CORE at access mode and then we run ospf between LAN core and WAN

But we can assign IP to interface of both LAN core & WAN so why we assign IP via SVI?

ANY reason

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VIP Mentor

Re: Vlan requirement between router and switch

depends on the requirement, if no other vlan required between that link, best approach to configure at interface level and enable OSPF neighbourship.

 

 

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Re: Vlan requirement between router and switch


@knaik99 wrote:

But we can assign IP to interface of both LAN core & WAN so why we assign IP via SVI?

ANY reason


The main reason - the SVI will only go down if all the assigned interfaces in that VLAN go down. Until one interface is in UP/UP state the SVI will stay UP. It provides redundant links.

Lets say .. you have a faulty port/cable and you wanted to replace it .. if you disconnect the OSPF will drop .. but if had an SVI .. you could easily configure a different port to access the same vlan and connect cable to new ports and remove from old ports. Depending on the config (OSPF timers/spanning-tree portfast).. it would not drop the OSPF neighbours if one of the cables was disconnected or port was shut.

 

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Hall of Fame Guru

Re: Vlan requirement between router and switch

I agree with @balaji.bandi that the answers to the question in the original post depend on requirements and on the environment. The original post suggests a very simple environment with a single switch connecting to a single router using a single link. And in that case it is difficult to see much advantage for SVI over configuring the switch port as a routed interface. But what if the environment were different? What if there were a single switch but there were 2 routers and if you wanted to run HSRP between the routers to provide failover capability for the connection. You could do that with an SVI but could not do that with a routed interface. Or what if there were 2 switches connected to a single router, and you wanted HSRP for redundancy for the switches. Again an SVI would make that possible while a routed interface would not. And in a situation that many of us have experienced of 2 switches connected to 2 routers so that there is redundancy for both the switch side and the router side? Again we find that an SVI does support this while a routed interface would not.

HTH

Rick
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