Layer 3 Switches – How to Connect Different Networks Based on VLANs Using Layer 3 Switches and Router

ciscoeigrplayer3packet-tracerrouting

diagram

This is a simplified version of my network diagram. How do I make both network speak to each other?

I'm confused because earlier I used routers and switches, and I connected them using OSPF or EIGRP. Now, I've tried to set up EIGRP on the layer 3 switch and then on the router but I still can't ping from one network to another. I just can't understand the concept of layer 3 switches in conjunction with vlans.

These are my switches' configurations:

Switch 1:

int fa0/1
 switchport access vlan 35
!
int fa0/2
 switchport access vlan 40
!
int fa0/3
 switchport access vlan 45
!
int fa0/4
 switchport access vlan 50
!
int gig0/1
 switchport trunk encapsulation dot1q 
 switchport mode trunk
!

Switch 2:

int fa0/1
 switchport access vlan 45
!
int fa0/2
 switchport access vlan 55
!
int fa0/3
 switchport access vlan 40
!
int fa0/4
 switchport access vlan 60
!
int gig0/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
int vlan 35
 ip address 10.100.50.17 255.255.255.240
!
int vlan 40
 ip address 10.100.50.33 255.255.255.240
!
int vlan 45
 ip address 10.100.50.49 255.255.255.240
!
int vlan 50
 ip address 10.100.50.65 255.255.255.240
!
int vlan 55
 ip address 10.100.50.81 255.255.255.240
!
int vlan 60
 ip address 10.100.50.97 255.255.255.240
!
exit
!
ip dhcp pool vlan35
network 10.100.50.16 255.255.255.240
default-router 10.100.50.17
!
ip dhcp pool vlan40
network 10.100.50.32 255.255.255.240
default-router 10.100.50.33
!
ip dhcp pool vlan45
network 10.100.50.48 255.255.255.240
default-router 10.100.50.49
!
ip dhcp pool vlan50
network 10.100.50.64 255.255.255.240
default-router 10.100.50.65
!
ip dhcp pool vlan55
network 10.100.50.80 255.255.255.240
default-router 10.100.50.81
!
ip dhcp pool vlan60
network 10.100.50.96 255.255.255.240
default-router 10.100.50.97
!
exit
!
end
!

The same thing is configured on another network which has 192.168.85.xx network address. I can ping from one VLAN to another inside one network but I can't do it between two networks.

I also wonder if I have to write the ip routing command on interface of the switch which is directly connected with the router.

Best Answer

Unless you enable routing on a layer-3 switch, it is only doing layer-2 switching, not anything with layer-3.

How do you suppose that the networks on one side know where to send traffic destined for the networks on the other side? Routers, including layer-3 switches, need to know where to send traffic, otherwise the traffic gets dropped. Routers get routers three ways:

  1. Directly connected networks
  2. Statically configured routes
  3. Dynamically learned routes from routing protocols

You either need to manually configure routes, or you need to run a routing protocols between the layer-3 devices.

The real way to do it is to configure IP routing on all the layer-3 switches, and configure the links between the layer-3 switches and the router to be routed links, not trunks. Then you run a common routing protocol on all the layer-3 devices.

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