IS-IS Lab 13 Implement L2 Flat topology

Previous  Next

Download Lab: VIRL | EVE-NG | GNS3

Image requirements:

Cisco IOSv (vios-adventerprisek9-m.vmdk.SPA.156-2.T)

To understand the benefits of hierarchical network design one needs to comprehend the flat networks and their limitations, this lab is the preparation for the future multi-areas IS-IS labs, this scenario is ideal to build the core network of ISP or a large enterprise, the topology described here, is good for MPLS implementation using IS-IS as an IGP. The main task is to configure the entire infrastructure as one IS-IS L2 domain then enable MPLS to switch packets using labels. Perform all necessary tasks as outlined in the "Lab tasks" section.

Nodes Access: 
Enable:       cisco 
Username:  cisco 
Password:   cisco 

Lab tasks: 

1. Configure integrated IS-IS routing protocol on all routers in the topology for IPV4 only, change IS-type and circuit-type to L2 only. Enable IS-IS routing on the interfaces according to the diagram. For NET, pick any for a System-ID part of NSAP. 

2. Verify the IS-IS implementation with show commands as well as use ping and traceroute to confirm the IPv4 connectivity. 

3. Configure MPLS to enable packet switching with labels, use a range of 100 labels per node, for example, router C1 will have a range between 100 and 199. 

4. Verify MPLS implementation and check that the output of the traceroute command contains outgoing labels for some hops the packets traverse. 


Lab procedure: 

Task 1&2:

Step1: Begin with core router C1 enter the router isis mode then configure the NET address, change IS-type to layer 2 only. 

C1(config)#router isis
C1(config-router)#net 49.C000.0000.0000.00C1.00
C1(config-router)#is-type level-2-only

Step2: Specify the range of the interfaces to participate in the IS-IS routing process, including the interface loopback 0. Configure the circuit-type.

C1(config)#interface range g0/1-3, lo0
C1(config-if-range)#ip router isis
C1(config-if-range)#isis circuit-type level-2-only  


Step3: Verify IS-IS configurations with the following command:

C1#show  isis protocol
IS-IS Router: <Null Tag>
  System Id: 0000.0000.00C1.00  IS-Type: level-2
  Manual area address(es):
  Routing for area address(es):
  Interfaces supported by IS-IS:
        Loopback0 - IP
        GigabitEthernet0/3 - IP
        GigabitEthernet0/2 - IP
        GigabitEthernet0/1 - IP
    static (on by default)
  Distance for L2 CLNS routes: 110
  RRR level: none
  Generate narrow metrics: level-1-2
  Accept narrow metrics:   level-1-2
  Generate wide metrics:   noneC1

  Accept wide metrics:     none

Step4: Configure the rest of the nodes by repeating steps 1 through 3. 

Step5: Verify neighbors on the core routers, then from router E2 ping every loopback IP address in the topology, sourcing it from loopback0. Trace the path from router E2 to router A2.

C1#show  isis neighbors  
System Id       Type Interface     IP Address      State Holdtime Circuit Id
A1              L2   Gi0/2        UP    22       C1.02             
C2              L2   Gi0/1       UP    7        C2.01             
D1              L2   Gi0/3        UP    7        D1.02   

E2#ping source lo0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Packet sent with a source address of
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/7 ms

Type escape sequence to abort.
Tracing the route to
VRF info: (vrf in name/id, vrf out name/id)
  1 3 msec 3 msec 3 msec
  2 6 msec 3 msec 3 msec
  3 5 msec 4 msec 4 msec
  4 5 msec 6 msec 6 msec
  5 5 msec *  7 msec

Task 3&4:

Step1: Configure MPLS on every node in the topology. Begin from core router C1 and C2, in global configuration mode set label range and enable MPLS then specify which interface participating in MPLS switching under the interface configuration. All GigEthernet interfaces interconnecting nodes should be enabled for MPLS.

C1(config)#mpls label range 100 199
C1(config)#mpls ip
C1(config)#interface  range g0/1-3
C1(config-if-range)#mpls ip
C1(config-if-range)# exit

Step2: LDP makes label switching happened, so using the appropriate show commands, verify its neighborship and MPLS label forwarding-table. 

C1#show  mpls ldp neighbor
    Peer LDP Ident:; Local LDP Ident
        TCP connection: -
        State: Oper; Msgs sent/rcvd: 53/53; Downstream
        Up time: 00:27:50
        LDP discovery sources:
          GigabitEthernet0/1, Src IP addr:
        Addresses bound to peer LDP Ident:

 Peer LDP Ident:; Local LDP Ident
        TCP connection: -
        State: Oper; Msgs sent/rcvd: 50/50; Downstream
        Up time: 00:24:58
        LDP discovery sources:
          GigabitEthernet0/2, Src IP addr:
        Addresses bound to peer LDP Ident:
    Peer LDP Ident:; Local LDP Ident
        TCP connection: -
        State: Oper; Msgs sent/rcvd: 37/37; Downstream
        Up time: 00:13:11
        LDP discovery sources:
          GigabitEthernet0/3, Src IP addr:
        Addresses bound to peer LDP Ident:

There are three LDP neighbors of the router C1, in the output lines begin with italic "Peer LDP Ident:" represent MPLS neighbors. 

C1#show  mpls forwarding-table Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop   
Label      Label      or Tunnel Id     Switched      interface             
100        202     0             Gi0/1  
101        203     0             Gi0/1  
102        Pop Label     0             Gi0/1  
103        Pop Label     686           Gi0/2   
104        Pop Label     0             Gi0/3   
105        Pop Label     0             Gi0/1  
106        206   0             Gi0/1  
107        Pop Label   0             Gi0/2   
108        Pop Label   0             Gi0/3   
109        210   0             Gi0/1  
110        211   0             Gi0/1  
111        212   2380          Gi0/1  
112        Pop Label   672           Gi0/1  
113        714   0             Gi0/3   
114        315  1476          Gi0/2    

This table shows local and outgoing labels for all subnets IS-IS learned about in the topology. 

Additionally, these show commands give more insights into MPLS cloud implementation: 

C1#show  mpls  interfaces
Interface              IP            Tunnel   BGP Static Operational
GigabitEthernet0/1     Yes (ldp)     No       No  No     Yes       
GigabitEthernet0/2     Yes (ldp)     No       No  No     Yes       
GigabitEthernet0/3     Yes (ldp)     No       No  No     Yes  

On the local router, it shows which interfaces participating in the label switching. 

C1#show  mpls  label range
Downstream Generic label region: Min/Max label: 100/199 

Shows configured range of labels on the local router. 

Step3: Using traceroute to on the router E2, identify outgoing labels routers use to switch packets to the destination. 

E2#traceroute source  lo0
Type escape sequence to abort.
Tracing the route to
VRF info: (vrf in name/id, vrf out name/id)
  1 [MPLS: Label 915 Exp 0] 9 msec 8 msec 7 msec
  2 [MPLS: Label 214 Exp 0] 7 msec 7 msec 7 msec
  3 [MPLS: Label 114 Exp 0] 7 msec 6 msec 5 msec
  4 [MPLS: Label 315 Exp 0] 6 msec 5 msec 5 msec
  5 6 msec *  8 msec

From the output, you can determine that router E2 uses E1's label 915 when the packet reaches E1 it uses label 214 of C2, well router C2 to switch packet utilizes the label 114 of C1, and router C1 takes label 315 to pass the packet to A1. Lastly, the router A1 pops the label and switch pure IPv4 to the A2 since the A2 is where IP address resides it does not need MPLS to forward data.


Popular Posts