SLIRP is a clever tool that turns network traffic (raw IP frames on one side) into connect(2), read, write etc system calls on the other side. eg. If it sees a virtual machine is making a connection by sending a TCP SYN packet, it will on one side turn that into a connect(2) system call, and on the other side send back the appropriate TCP packets to complete the connection. It also does ARP, DNS, etc. If you think of a kernel as something that turns socket system calls into packets, then SLIRP is the opposite.
SLIRP is mainly useful when you don't have (or don't want) root permissions to send raw packets. I may be one of the few people here to have used SLIRP back in the early 90s for its original purpose: You have dial up access to a shared SunOS terminal login, how do you turn that into a full network connection for your local Linux PC? SLIRP (+ expect, SLIP and some scripting) solved this exact problem.
Passt (https://passt.top/passt/about/) is a more modern replacement for SLIRP that amongst other things fully supports IPv6 and is more secure architecturally (runs in a separate process, uses modern Linux mechanisms for isolation etc). There was a talk about it here: https://kvmforum2022.sched.com/event/15jJY/slirp-is-dead-lon...
This pull request is using Pasta which is something on top of Passt that does something with network namespaces which I'm not entirely clear on, but some docs here: https://passt.top/passt/about/#pasta-pack-a-subtle-tap-abstr...
SLIRP is mainly useful when you don't have (or don't want) root permissions to send raw packets. I may be one of the few people here to have used SLIRP back in the early 90s for its original purpose: You have dial up access to a shared SunOS terminal login, how do you turn that into a full network connection for your local Linux PC? SLIRP (+ expect, SLIP and some scripting) solved this exact problem.
Passt (https://passt.top/passt/about/) is a more modern replacement for SLIRP that amongst other things fully supports IPv6 and is more secure architecturally (runs in a separate process, uses modern Linux mechanisms for isolation etc). There was a talk about it here: https://kvmforum2022.sched.com/event/15jJY/slirp-is-dead-lon...
This pull request is using Pasta which is something on top of Passt that does something with network namespaces which I'm not entirely clear on, but some docs here: https://passt.top/passt/about/#pasta-pack-a-subtle-tap-abstr...