Problem Impact Statement:

• User might experience the traffic drop. On PTX1k trapstat 252 "sw.nh.discard_sampling_trap"

---(refreshed at 2023-11-17 16:36:23 PST)---
0 ( 252) sw.nh.discard_sampling_trap 7719311 1168
3 ( 252) sw.nh.discard_sampling_trap 8121484596 1226344

---(refreshed at 2023-11-17 16:36:32 PST)---
0 ( 252) sw.nh.discard_sampling_trap 7730120 1164 
3 ( 252) sw.nh.discard_sampling_trap 8132820972 1224990

• In the problem state service route points to Blackhole/Discard NH.
• The command "show route <service route> extensive expanded-nh" can be used to see the issue.

> show route 20.0.0.0/25 extensive expanded-nh 
20.0.0.0/25 (3 entries, 1 announced) 
Installed-nexthop:
List (0xd94139c) Index:2097157
	Indr (0x83cc91c) 250.10.41.249 Session-ID: 0x158 
		Krt_inh (0x5ea2008) Index:2097175 PNH: 250.10.41.249
			Chain Fully resolved tunnel (0x83cc4bc) Index:680 IPoIP src 1.1.1.2 dest 250.253.254.255 tunnel-endpoint 249.4.253.207 
				Frr_inh (0x83cac5c) Index:2097154 PNH: 250.253.254.255 Session-ID: 0x163
					Blackhole (0x507119c)
	Indr (0x83ca4dc) 250.10.41.251 Session-ID: 0x150
		Krt_inh (0x5ea1208) Index:2097177 PNH: 250.10.41.251
			Chain Fully resolved tunnel (0x83cc0fc) Index:665 IPoIP src 1.1.1.2 dest 250.253.254.255 tunnel-endpoint 249.4.253.208
				Frr_inh (0x83cac5c) Index:2097154 PNH: 250.253.254.255 Session-ID: 0x163 
					Blackhole (0x507119c)
	Indr (0x83cbc9c) 250.10.41.252 Session-ID: 0x155 
		Krt_inh (0x5ea1c08) Index:2097188 PNH: 250.10.41.252
			Chain Fully resolved tunnel (0x83cbbfc) Index:666 IPoIP src 1.1.1.2 dest 250.253.254.255 tunnel-endpoint 249.4.253.209 
				Frr_inh (0x83cac5c) Index:2097154 PNH: 250.253.254.255 Session-ID: 0x163
					Blackhole (0x507119c)

• Run the below command with service route prefix, make sure “Blackhole” is not present in the below command display - show route <prefix> extensive expanded-nh 
• Service route is pointing to a blackhole NH when user deactivated the BGP protocol on the TRA router after withdrawing service route from the same TRA router.
• Deactivating BGP protocol will cause churn on the BGP routes on the DUT.
• On DUT, the tunnel end-point resolves over BGP route. Due to the churn in BGP route, there will be a change in the forward route.
• A static route with discard was picked as its forwarding route which made the route to point to a black hole.
• During forward route evaluation, currently, we do not have any checks if the next-hop is of type discard. This caused the issue.