How does ttl work?

Question

Computer networks

Hello! I have a question. I collected a network in CPT, as in the screenshot. From the Server1 server (on the right) I ping the l3 switch on the left. Initially, a package is created with ttl=255. Then it goes to Router5, where outgoing ttl=255. Why is that? After all, should the value decrease by 1 between two routers?
Further from Router4 it goes to Router3, where it should be ttl -1. In general, before Router0, everything happens as expected, a packet ttl=251 arrives at Router0, and the outgoing one is already ttl=253, and the switch arrives at l3 with such ttl. Why did it increase, and immediately by 2?
Between R0 and R5 ipsec vpn is configured.

Answer 1

Apparently you are looking at different packages.
If I understand you correctly, Server0 - L3 Switch traffic goes inside ipsec.
On R5(255) - R4(254) - R3(253) - R2(252) - R1(251) - R0, the ipsec packets themselves go, which are formed on R5 with ttl 255, they will come to R0 already with TTL 251.
For packets from Server0, the scheme will be Server0 (255) - R5 (254) - R0 (253) - L3 Switch, respectively, TTL at the input to the switch will be 253