Please find the following show information.
Could any expert help me understand, why the shamlink hidden in VPN.inet.0?
RE0> show ospf route instance VPN Topology default Route Table:Prefix Path Route NH Metric NextHop Nexthop Type Type Type Interface Address/LSP172.20.232.0/25 Ext2 Network IP 0 shamlink.0
RE0> show route table VPN.inet.0 protocol ospf 172.20.232.0/25 hidden VPN.inet.0: 721 destinations, 1460 routes (721 active, 0 holddown, 16 hidden)+ = Active Route, - = Last Active, * = Both172.20.232.0/25 [OSPF] 9w2d 09:44:14, metric 0, tag 0 > via shamlink.0
RE0> show route table VPN.inet.0 protocol bgp 172.20.232.0/25 VPN.inet.0: 721 destinations, 1460 routes (721 active, 0 holddown, 16 hidden)+ = Active Route, - = Last Active, * = Both172.20.232.0/25 [BGP/170] 15w6d 08:36:14, localpref 801, from 22.214.171.124 AS path: I > to 10.79.129.109 via xe-9/3/0.0, label-switched-path FPE.JRT004-to-FPE.JRT003_02 to 10.79.128.109 via xe-11/3/0.100, label-switched-path FPE.JRT004-to-FPE.JRT003_01
This is working as designed ,see RFC 4577 section 126.96.36.199 https://www.rfc-editor.org/rfc/rfc4577.txt
188.8.131.52. Routing and Forwarding on Sham Links
If a PE determines that the next hop interface for a particular route
is a sham link, then the PE SHOULD NOT redistribute that route into
BGP as a VPN-IPv4 route.
Any other route advertised in an LSA that is transmitted over a sham
link MUST also be redistributed (by the PE flooding the LSA over the
sham link) into BGP. This means that if the preferred (OSPF) route
for a given address prefix has the sham link as its next hop
interface, then there will also be a "corresponding BGP route", for
that same address prefix, installed in the VRF. Per Section 4.1.2,
the OSPF route is preferred. However, when forwarding a packet, if
the preferred route for that packet has the sham link as its next hop
interface, then the packet MUST be forwarded according to the
corresponding BGP route. That is, it will be forwarded as if the
corresponding BGP route had been the preferred route. The
"corresponding BGP route" is always a VPN-IPv4 route; the procedure
for forwarding a packet over a VPN-IPv4 route is described in [VPN].
This same rule applies to any packet whose IP destination address is
the remote endpoint address of a sham link. Such packets MUST be
forwarded according to the corresponding BGP route.
Your packets destined to 172.20.232.0/25 have to be forwarded along the BGP route, there is no other choice.
Sham link is only serving to avoid conversion of LSA1/2 to LSA3, it does not serve any purpose for LSA5 from which Your 172.20.232.0/25 OSPF route originates (OSPF Ext2).