Difference between route with a switch and with a router

[Marco Pérez]

Hi, all,

I am studying for my CCNP R&S, I'll be making the SWITCH exam in 3 weeks but there are somethings that aren't clear for me. 

Can you help me to understand the difference between route with a Router and with a Switch? I mean, when and why should I use OSPF in a router instance to use a switch?

Regards.

[Daniel Ordóñez Flores]

Hi @Marco Pérez

I'm not sure about what are u asking. You want to know, if is better make routing on the route or switch?

Or you are asking when to use OSPF between them?

[Marco Pérez]

My question was oriented and what is better and when should I run a routing protocol like OSPF in one interface VLAN and when in a L3 interface. And if both cases OSPF works in a different way.

Thanks, Daniel!

[Julio E. Moisa]

Hi Marco,

There is different perspective if you use a Physical layer 3 port or a SVI,  cases:

Physical layer 3 port (switch or router), used to connect to other Layer 3 device directly. (Connect a cable on the switch and the other end to the router) and then you can include the network segment into OSPF on both devices, it will create OSPF adjacency.

int g1/0/1

description TO-ROUTER

no switchport

ip address 10.0.0.1 255.255.255.252

no shut

Using SVI, imagine the case you have 2 robust switches like 6800 and you want to enable routing between them but the link used to create the point to point between them is layer 2 (trunk), so you can create a VLAN and the SVI and enable OSPF 

SWITCH 1

ip routing 

vlan 10

interface vlan 10

ip add 10.0.0.1 255.255.255.252

no shut

inter g1/0/24

description TO-SWITCH2

switchport mode trunk

no shut

router ospf 100

network 10.0.0.0 0.0.0.3 area 0

SWITCH 2

ip routing 

vlan 10

interface vlan 10

ip add 10.0.0.2 255.255.255.252

no shut

inter g1/0/24

description TO-SWITCH1

switchport mode trunk

no shut

router ospf 100

network 10.0.0.0 0.0.0.3 area 0

This option is like enable routing over layer 2 link, both solutions will work as normal for any routing protocol. 

Hope it is useful

:-)

[Julio E. Moisa · Accepted solution]

Hi Marco,

Actually there are no major differences between the routing between a switch over a router, a switch can execute the same routing processes than a router. Now take in consideration that a switch will need specific licenses to run routing protocols, for example: Cisco Catalyst 3650/3850 will need IP Base or IP Services to execute routing protocols, Cisco Catalyst 9000 will need an advantage license. 

Routers were designed to be layer 3 (routing) but in order to run specific features, I suggest verify the IP base and IP services licenses differences. For example if you want to run BGP. 

OSPF can be implemented over a switch or router now take in consideration the information above. 

Hope it is useful on answered your question. 

:-)

[Marco Pérez]

Thank you very much, Julio. This is the response that I was waiting for! Regards.