R3 prepends its AS and sends it outbound to R1 in AS 100. Because R1 and R2 are in one iBGP domain (AS 100), all traffic from AS 100 will prefer to use a shorter AS path to AS 200 which is R4's link.

Cisco IOS XE supports the Yet Another Next Generation (YANG) data modeling language. YANG can be used with the Network Configuration Protocol (NETCONF) to provide the desired solution of automated and programmable network operations. NETCONF(RFC6241) is an XML-based protocol that client applications use to request information from and make configuration changes to the device. YANG is primarily used to model the configuration and state data used by NETCONF operations.
Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/16-
5/configuration_guide/prog/b_165_prog_9500_cg/data_models.pdf
Note: Although NETCONF also uses XML but XML is not a data modeling language.

VPN 0 - Transport VPN, which carries control traffic via the configured WAN transport interfaces.
Initially, VPN 0 contains all of a device's interfaces except for the management interface, and all interfaces are disabled.
VPN 512 - Management VPN, which carries out-of-band network management traffic among the Viptela devices in the overlay network. The interface used for management traffic resides in VPN
512. By default, VPN 512 is configured and enabled on all vEdge routers except for vEdge 100.
For controller devices, by default, VPN 512 is not configured.
VPNs 1 through 511, and 513 through 65530 - VPNs on vEdge routers for service-side data traffic.
https://www.cisco.com/c/en/us/support/docs/routers/12000-series-routers/47321-ciscoef.html

An ITR is responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites. When the ITR receives a packet destined for an EID, it first looks for the EID in its mapping cache. If the ITR finds a match, it encapsulates the packet inside a LISP header with one of its RLOCs as the IP source address.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-mt/irl-15-mt- book/irl-overview.pdf