Basic Routing on Multilayer Switch - Connected Network - No VLAN

Today, we are going to try connectivity between two networks, connected by a multilayer switch.

Topology

We see two networks 172.16.0.0 (inside) and 5.0.0.0 (outside). Inside laptop with 172.16.0.10 and Outside laptop with 5.0.0.10.  We check for ping between inside and outside laptops.

Task Breakup

1. Configuring IP address on Laptops
2. Configure IP address on Switch
3. Analysis before routing
4. Configure routing on switch
5. Analysis after routing

1. Configuring IP address on Laptop

Click on Laptop -> Desktop -> IP Configuration

Inside - Laptop - IP Configuration

Outside - Laptop - IP Configuration

2. Configure IP addresses on Switch

As it is multilayer switch, we have to convert the interface into routing interface instead of switch interface.  'no switchport' is the command we use.  We set the interface according to the details mentioned in Topology.

routing#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
routing(config)#int gig 1/0/1
routing(config-if)#no switchport 
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to up

routing(config-if)#ip address 172.16.0.1 255.255.0.0
routing(config-if)#no shut
routing(config-if)#exit

routing(config)#int gig 1/0/10
routing(config-if)#no switchport
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/10, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/10, changed state to up

routing(config-if)#ip address 5.0.0.1 255.0.0.0
routing(config-if)#no shut
routing(config-if)#exit

3. Analysis before Routing

Enable debugging at packet level

routing#debug ip packet 
Packet debugging is on
routing#

IP Routing information will be empty

routing#show ip route 
Default gateway is not set

Host               Gateway           Last Use    Total Uses  Interface
ICMP redirect cache is empty

Ping from Inside Laptop and Outside Laptop will not happen

4. Configuring routing on switch

routing#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
routing(config)#ip routing
routing(config)#exit
routing#

Routing information will be populated with connected networks

routing#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

C    5.0.0.0/8 is directly connected, GigabitEthernet1/0/10
C    172.16.0.0/16 is directly connected, GigabitEthernet1/0/1

5. Analysis after Routing

Issue ping from Inside laptop(172.16.0.10) to outside laptop(5.0.0.2) .  It will be successful !!!

As packet debug is enabled, we will see the following dumps.

IP: tableid=0, s=172.16.0.10 (GigabitEthernet1/0/1), d=5.0.0.2 (GigabitEthernet1/0/10), routed via RIB

IP: s=172.16.0.10 (GigabitEthernet1/0/1), d=5.0.0.2 (GigabitEthernet1/0/10), g=5.0.0.2, len 128, forward

IP: tableid=0, s=5.0.0.2 (GigabitEthernet1/0/10), d=172.16.0.10 (GigabitEthernet1/0/1), routed via RIB

IP: s=5.0.0.2 (GigabitEthernet1/0/10), d=172.16.0.10 (GigabitEthernet1/0/1), g=172.16.0.10, len 128, forward

First 2 lines, indicates the routing process that happened for ICMP Echo Request packet with source IP(inside laptop) and destination IP (outside laptop)

Next 2 lines, indicates the routing process of ICMP Echo Reply packet with source IP (outside laptop) and destination IP(inside laptop)