1

This is my topology in my network.

enter image description here

It's easy to know my server can communicate to 172.18.32.254/24.

But when I traceroute the path, I only get one hop to it.

enter image description here

My doubt is why it do not through 102.10.10.254?

2

Based on your diagram, it looks like the "gateway switch" is one device (a router) with multiple IP addresses: 172.18.32.254 and 102.10.10.254.

Your server 102.10.10.1 originates the first traceroute packet with a TTL of 1. The packet arrives at the "gateway switch" on the 102.10.10.254/ibr.100 interface. The packet is accepted. The router notices that one of its own ip addresses (172.18.32.254) is the destination and delivers the traceroute packet to the upper-layer stack for processing. This results in a response from 172.18.32.254.

Going between 102.10.10.254 and 172.18.32.254 does not count as a "hop" because that is the same device.

The original traceroute packet never has its ttl decremented. Per When is an IPv4 TTL decremented and what is the drop condition? a router only decrements a ttl once it has decided to forward it.

More simply, your server IS ONE NETWORK HOP from 172.18.32.254. Multiple interfaces/ips on a router is not a hop.

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0

There is no hop for traceroute to see in between 172.18.32.254 and 102.10.10.254 since these are bound on the same device.

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