Connecting Layer 2 switchport to layer 3 port

Question

I have a config that I am trying to bring up, and in my mind it should work, but perhaps I am missing something.

The idea is that one end of the link is a layer 3 interface on a router. The other end is a switchport trunk, on a vlan with an IP interface. They should be able to communicate, no?

RTR1

Interface 0/1
ip address 192.168.50.10 255.255.255.0

SW1 - Layer 3 switch

Interface 1/0/10
 # switchport
 # switchport mode trunk
 # switchport trunk allowed vlan 50

vlan 50
 # name test vlan

Interface vlan 50
* ip address 192.168.50.20 255.255.255.0*

There are no gateways configured on either devices, but that should not matter? All I am trying to do is reach them directly.

# ping 192.168.50.20 source int0/1

or

# ping 192.168.50.10 source vlan 50

neither works. The physical connection is good because both devices see each other as CDP neighbors. The Interfaces are both up/up, vlan 50 interface is up. The subnet is in each device's routing table, as directly connected.

Any help would be appreciated. Am i missing something?

thank you

Answer 1

With your switch configuration, you are adding VLAN tags to the frames, but the router is not, so the switch assumes the traffic belongs to VLAN 1.

Since this is layer-3 switch, you should simply configure the switch interface as a layer-3 interface:

interface 1/0/10
 no switchport
 ip address 192.168.50.20 255.255.255.0
!

Alternatively, you could configure a trunk on the router interface.

interface 0/1
 no ip address
!
interface 0/1.50
 encapsulation dot1Q 50
 ip address 192.168.50.10 255.255.255.0
!

Answer 2

Depending on your needs, the best configuration may vary significantly. Alternatively, on SW1:

you could add -

interface 1/0/10
    switchport trunk native vlan 50

The actual issue in this case is that the switch needs to take the tag off the frame before forwarding it the the router, due to being layer 2 adjacent. Ron explains why above, and this is considered best practice.

However, you can still use your router interface config if you add the command I noted above to the trunk.

Answer 3

There are two option feasible to ensure connectivity through router and layer3 switch.

Option 1

In Router

Router(config) # int 0/1

Router(config)# ip address 192.168.50 .10 255.255.255.0

Router(config) # no shut

Layer3 switch

Switch (config) # int 1/0/10

Switch(config)#switchport

Switch(config)#switch port mode access

Switch(config)#switch access vlan 50

Switch (config)no shutdown

In layer3 switch L2 VLAN need to create

Option 2

In router

Router(config) #int 0/1

Router(config) #ip address 192.168.50.10 255.255.255.0

Router(config) # no shut

Layer3 switch

Switch(config)# int 1/0/10

Switch(config)#no Switchport

Switch(config)#ip address. 192.168.50.20 255.255 .255.0

Switch(config)#no shutdown

Static route configuration need to configure in router and layer3 switch to route required tràffic from router to switch vise versa .