The scenario describes a Carrier Supporting Carrier (CSC) architecture where the Customer Edge (CE) router needs to exchange both IPv4 routing information and MPLS labels with the Provider Edge (PE) router over an external BGP (eBGP) session.
Looking closely at the configuration in the exhibit:
- On the PE Router, under the VRF BGP neighbor configuration (neighbor 192.168.1.24), the address-family ipv4 labeled-unicast command is applied. This means the PE is fully prepared to send and receive BGP Labeled Unicast (BGP-LU) updates.
- On the CE Router, under address-family ipv4 unicast, it has configured allocate-label all, but it is missing the corresponding activation command under the neighbor statement to actually negotiate labeled unicast capabilities with its peer (neighbor 192.168.1.25).
Without activating the ipv4 labeled-unicast address-family for the neighbor on the CE router, the eBGP session will only exchange standard IPv4 unicast routes, breaking the end-to-end LSP required for CSC.

A 6PE deployment uses MP-BGP's IPv6 address family to carry IPv6 routes over an IPv4 MPLS core. On IOS XR, you enable this with the address-family ipv6 unicast stanza under the BGP process alongside allocate-label all.