vrf: Clones VPN paths with different RD and matched RTs

[iwaseyusuke]

When VPN routes are shared between different VPNs (or VRFs) for example, the RDs assigned for each VRF can differ from others, but the same RT should be used. In this case, the duplicated IP unicast routes can be selected as the best path because VPN prefix ":" is different and GoBGP calculates the best path on the global table context. For example,

$ gobgp vrf add 1 rd 1:1 rt both 1:1
$ gobgp global rib -a vpnv4 add 10.0.0.0/24 label 0 rd 1:1 rt 1:1
$ gobgp global rib -a vpnv4 add 10.0.0.0/24 label 0 rd 2:2 rt 1:1
$ gobgp global rib -a vpnv4
   Network              Labels     Next Hop             AS_PATH              Age        Attrs
*> 1:1:10.0.0.0/24      [0]        0.0.0.0                                   00:00:00   [{Origin: ?} {Extcomms: [1:1]}]
*> 2:2:10.0.0.0/24      [0]        0.0.0.0                                   00:00:00   [{Origin: ?} {Extcomms: [1:1]}]
$ gobgp vrf 1 rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
   10.0.0.0/24          0.0.0.0                                   00:00:10   [{Origin: ?}]  <--- RD 1:1 on global
   10.0.0.0/24          0.0.0.0                                   00:00:10   [{Origin: ?}]  <--- RD 2:2 on global

The both of the above VRF routes are selected as the best path unexpectedly.

This patch clones the received VPN path before installing the global table and overwrites the RD of the cloned paths by the RD of the matched VRFs. Also filters out the duplicated path on each VRF.

$ gobgp vrf add 1 rd 1:1 rt both 1:1
$ gobgp global rib -a vpnv4 add 10.0.0.0/24 label 0 rd 2:2 rt 1:1
$ gobgp global rib -a vpnv4
   Network              Labels     Next Hop             AS_PATH              Age        Attrs
*> 1:1:10.0.0.0/24      [0]        0.0.0.0                                   00:00:00   [{Origin: ?} {Extcomms: [1:1]}]
*> 2:2:10.0.0.0/24      [0]        0.0.0.0                                   00:00:00   [{Origin: ?} {Extcomms: [1:1]}]
$ gobgp vrf 1 rib -a ipv4
   Network              Next Hop             AS_PATH              Age        Attrs
   10.0.0.0/24          0.0.0.0                                   00:00:10   [{Origin: ?}]
$ gobgp global rib -a vpnv4 del 10.0.0.0/24 label 0 rd 2:2
$ gobgp vrf 1 rib -a ipv4
Network not in table
$ gobgp global rib -a vpnv4
Network not in table

Note: This feature only takes effect for only MPLS VPNv4/v6 routes and does not have any for other address families which have RD on its NLRI (e.g., EVPN, FlowSpec for VPN).