aigate/docs/diagrams/linux-network.puml at main · AxeForging/aigate · GitHub

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@startuml linux-network
!theme plain
skinparam backgroundColor #FEFEFE
skinparam defaultFontName Inter
skinparam shadowing false
skinparam roundcorner 8
skinparam ArrowColor #444444
skinparam RectangleBorderColor #888888
skinparam PackageBorderColor #666666
skinparam NoteBackgroundColor #FFFDE7
skinparam NoteBorderColor #FBC02D

title **Linux Network Isolation**\nslirp4netns + iptables (no root required)

cloud "Internet" as internet #E0E0E0

rectangle "User Namespace\n(outer unshare --user)" as userns #FFF3E0 {

  rectangle "**slirp4netns**\nuser-mode networking\n(host network + user ns caps)" as slirp #B3E5FC

  rectangle "Network Namespace\n(inner unshare --net)" as netns #FFCDD2 {

    rectangle "**tap0** (10.0.2.100)" as tap0 #EF9A9A

    rectangle "**iptables OUTPUT chain**" as iptables #EF9A9A {
      rectangle "ACCEPT  lo (loopback)" as r1 #FFFFFF
      rectangle "ACCEPT  UDP/TCP :53 (DNS)" as r2 #FFFFFF
      rectangle "ACCEPT  upstream DNS servers" as r3 #FFFFFF
      rectangle "ACCEPT  resolved AllowNet IPs" as r4 #C8E6C9
      rectangle "REJECT  everything else" as r5 #FFCDD2
    }

    rectangle "**Sandboxed Process**\nclaude / cursor / aider" as proc #CE93D8
  }
}

proc -down-> iptables : outbound traffic
iptables -down-> tap0 : allowed
tap0 <-left-> slirp : tap attachment\nvia setns()
slirp <-up-> internet : forwarded

note right of slirp
  Runs **inside** user namespace
  (has CAP_SYS_ADMIN) but in the
  **host** network namespace.

  Creates tap0 in sandbox net ns,
  forwards packets to real network.

  Built-in DNS forwarder: 10.0.2.3
end note

note right of r4
  Hosts resolved **inside** namespace
  via getent ahostsv4 (same DNS the
  sandboxed process will use).
  Each host retries 3x to handle
  DNS startup delay.
end note

note left of tap0
  **resolv.conf** bind-mounted
  to point at 10.0.2.3
  (slirp4netns DNS forwarder)
end note

note right of proc
  **Dispatch logic:**
  AllowNet + slirp4netns found
  -> runWithNetFilter()
  AllowNet + no slirp4netns
  -> warn, run unrestricted
  No AllowNet
  -> run unrestricted
end note

@enduml