Multilink PPP 1

Multilink PPP (MLPPP) makes multiple parallel links act like one link from a layer 3 perspective. Then, when a router’s layer 3 routing decides to forward a layer 3 packet out the layer 3 MLPPP multilink interface, the router has to choose which of the several MLPPP-controlled links to use. To do that, the router’s MLPPP layer 2 logic takes over to load balance the message over the multiple links. This next lab gives you a chance to practice MLPPP configuration, starting from scratch, by configuring two serial links to be in one multilink PPP group. No muss, no fuss, just practice making MLPPP work on a pair of serial links.

Requirements

Configure MLPPP on both router R1 and R2 in the figure, so that the routers have a single subnet (172.16.12.0/24) used between the two routers. You should think of this lab as a complete configuration for MLPPP, but also think about any changes needed based on the initial configuration to this lab. Follow these requirements:

• Configure the two serial links to use MLPPP:
  • Use MLPPP interface 1
  • Use subnet 172.16.12.0/24
  • Give R1 an IPv4 address that ends with .1, and R2 an address that ends with .2
  • Do not use any PPP authentication
• As for the transition from the existing configuration, examine the initial configurations shown in this lab exercise, and decide whether or not any existing configuration needs to be updated as a result:
  • Check the OSPF configuration, and make changes as needed, so that both routers still become OSPF neighbors and still exchange routes for their LAN subnets
  • Check the IP addressing configuration to remove any IP address overlaps or remove any unnecessary IP addresses.
• As for the topology:
  • Assume all interfaces shown in the figure are up and working

Figure 1: MLPPP Topology

Initial Configuration

Examples 1 and 2 show the initial configurations on routers R1 and R2, respectively.

Example 1: Router R1 Initial Configuration

hostname R1
!
interface GigabitEthernet0/1
 no shutdown
 ip address 172.16.1.1 255.255.255.0
!
interface serial 0/0/0
 no shutdown
 clock rate 1536000
!
interface serial 0/0/0
 no shutdown
 clock rate 1536000
!
router ospf 1
 network 172.16.0.0 0.0.255.255 area 0

Example 2: Router R2 Initial Configuration

hostname R2
!
interface GigabitEthernet0/1
 no shutdown
 ip address 172.16.2.2 255.255.255.0
!
interface serial 0/0/0
 no shutdown
 clock rate 1536000
!
interface serial 0/0/0
 no shutdown
 clock rate 1536000
!
router ospf 1
 network 172.16.0.0 0.0.255.255 area 0

Answer on Paper, or Maybe Test in Lab

To answer on paper, or in a text editor, just write your answers. The next post will list my suggested solution. And with this particular lab, as worded, there should be only a single correct answer.

To test in lab, you cannot use VIRL, because this lab uses serial interfaces. However, you can use Packet Tracer or real hardware. Feel free to do the lab in either environment. You can use any serial interface numbers that you want to use.

If you do implement this lab, try these show commands to get some insights into your solution:

show ppp multilink

show interfaces multilink 2

show ip interface brief

show ip ospf interface