The routing table shows two equal-cost next hops for the prefix and both are installed in the forwarding table, which means the router is selecting both next hops for forwarding traffic. This indicates equal-cost multipath forwarding.
The forwarding table entry shows a load-balancing group containing both next hops, which reflects the default Junos behavior of performing load balancing across equal-cost paths when multiple next hops exist for the same route.

To influence the path taken through an autonomous system, the Multi-Exit Discriminator (MED) attribute can be used. By setting a lower MED on R2 for routes advertised to R1 and R3, it will make the path through R2 to the 203.0.113.0/24 network more preferable.

The problem occurs most frequently when you attempt to run OSPF between a Cisco router and another vendor router. The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces do not match. If the router with the higher MTU sends a packet larger that the MTU set on the neighboring router, the neighbor router ignores the packet.
A mismatched Maximum Transmission Unit (MTU) setting on OSPF interfaces can cause routers to get stuck in the ExStart state. OSPF requires that both sides of a link have the same MTU to form a full adjacency.

In Junos OS, IS-IS does not automatically export routes from the routing table into the IS-IS protocol. By default, no routes are advertised into IS-IS unless an explicit export policy is configured to control which prefixes should be advertised.

Update messages are exchanged between BGP peers in the Established state to advertise new routes, withdraw previously advertised routes, and share path attributes for reachable prefixes.
Notification messages are used to signal errors detected in the BGP session and immediately terminate the session when a protocol error occurs.