Customers look for the redundancy of lan and wan because of more uptime . In those scenarios , two routers  deploy at customer premises and two wan links from different PE are required. In this topology, I am assuming the customer is using the same service provider with redundant pops.  Hot Standby Routing Protocol aka HSRP with single group is deployed for lan and static routing is being used between PE and CE. R5 is having the higher priority and working as active router and R4 is working as standby router. 

        Figure 1

The traffic forwarding from CE always done by R5 and for the reverse traffic from PE to CE is done by adding static routes from both PE. 

Figure 2

Figure 2 depicts that R5 is working as active router for LAN subnet with priority 255 and R4 which is is working as standby router with priority 254.

Figure 3

Figure 4

Figure 3 and Figure 4 showing the routes added for LAN with gateway as CE ip address as shown in figure 1. These routes are added for reverse traffic from SP cloud to CE lan.

Figure 5

Figure 5 is showing explicitly that route reflector is receiving the same route of from different PE because of having the same metric, the smallest router-id route is considering as the best route for forwarding the traffic.  The RR is also working as PE/P router also. A vrf TEST is created with address which is used for testing purposes.

The result is clear as water that for forwarding of traffic from CE-PE; path R5-R3-RR is used and for reverse traffic from SP cloud path RR-R2-R4 is used.  Fgure 6 and Figure 7 is showing the same results.

Figure 6

Figure 7

These type scenarios could lead to the several problems. So during the design and implementation a care should be taken about the same forwarding and reverse path. Some applications are jitter sensitive and may lead to the business uptime issues.

This problem could be overridden by changing the increasing the cost between RR-R2 and this may lead to another issues. So the best is to use the BGP as PE-CE to manipulate the routes according to the needs.

Shivlu Jain