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Comment by magicalhippo | Hacker News Reader

I'm really stumped as to why they didn't eliminate ports when designing IPv6. Having the last bits in the address take the role of ports makes sense given the hierarchical nature of IPv6 addresses. The first bits specify the network (my home), next bits the device, and last bits the service/endpoint on that device.

It would also make parsing much easier given that they chose : as separator in the addresses.

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Ports operate a different layer in the OSI model - the transport layer, not the network layer (which IP operates on). Ports are TCP and UDP concepts (e.g., a different application can bind to TCP port 443 than UDP port 443, as they're essentially different ports). Some protocols don't have ports at all, e.g., ICMP, which instead has a "type".

OK sure but TCP/IP was not designed to follow the OSI model.

Sure, but so what?

Imagine you could only bind services to their standard ports. What's the difference between a service running on my computer having a unique ip address, or my machine having a unique ip address and only running that service?

Compatibility. Code written for layer 4 should be compatible even if layer 3 is changed. In practice much code had to be changed anyways, but the amount of violence applied to existing code was limited by not getting rid of ports. It's not just that either, but much else, including cognitive load.

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