Configuration guidelines
Follow these guidelines when you configure a tunnel policy:
To select a preferred tunnel, create a tunnel policy and specify the preferred tunnel with the preferred-path command. The destination address of the preferred tunnel identifies a peer PE so the PE will forward traffic destined for that peer PE over the preferred tunnel. If you specify multiple preferred tunnels that have the same destination address in a tunnel policy, only the first configured tunnel takes effect. If the first tunnel is not available, the second tunnel is used, and so forth. No load balancing will be performed on these tunnels. This method explicitly specifies an MPLS TE tunnel for an MPLS VPN, facilitating traffic planning. HP recommends that you use this method.
To select multiple tunnels for load sharing, create a tunnel policy and specify the tunnel selection order and the number of tunnels by using the select-seq load-balance-number command. A tunnel type closer to the select-seq keyword has a higher priority. For example, the select-seq lsp cr-lsp load-balance-number 3 command gives LSP higher priority. If no LSP is available or the number of LSPs is less than 3, VPN uses CRLSP tunnels. The tunnels selected by this method are not fixed, complicating traffic planning. HP recommends not using this method.
If you configure both methods for a tunnel policy, the tunnel policy selects tunnels in the following steps:
If the destination address of a preferred tunnel identifies a peer PE, the tunnel policy uses the preferred tunnel to forward traffic destined for the peer PE without using any other tunnels.
If not, the tunnel policy selects tunnels as configured by the select-seq load-balance-number command.
Figure 31: MPLS VPN tunnel selection diagram
As shown in Figure 31, PE 1 and PE 2 have multiple tunnels in between and they are connected to multiple MPLS VPNs. You can control the paths for VPN traffic by using one of the following methods:
Configure multiple tunnel policies, and specify a preferred tunnel for each policy by using the preferred-path command. Apply these policies to different MPLS VPNs to forward the traffic of each VPN over a specific tunnel.
Configure one tunnel policy, and use the select-seq load-balance-number command to specify the tunnel selection order and the number of tunnels for load balancing. Apply the tunnel policy to MPLS VPNs to forward the traffic of every VPN over multiple tunnels.
The second method distributes traffic of a single VPN to multiple tunnels. The transmission delays on different tunnels can greatly vary. Therefore, the destination device or the upper layer application might take a great time to sequence the packets. HP recommends not using the second method.