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wgengine/router: add more documentation.

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This commit is contained in:
David Anderson 2020-05-07 18:30:37 +00:00
parent c9de43cd59
commit 78b1ed39ea
1 changed files with 14 additions and 6 deletions
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20
wgengine/router/router_linux.go
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@ -226,11 +226,6 @@ func (r *linuxRouter) SetRoutes(rs RouteSettings) error {
return errq return errq
} }
var tailscaleCGNATRange = wgcfg.CIDR{
IP: wgcfg.IPv4(100, 64, 0, 0),
Mask: 10,
}
const ( const (
tsConf = "/etc/resolv.tailscale.conf" tsConf = "/etc/resolv.tailscale.conf"
backupConf = "/etc/resolv.pre-tailscale-backup.conf" backupConf = "/etc/resolv.pre-tailscale-backup.conf"
@ -503,6 +498,11 @@ func (r *linuxRouter) delNetfilter4() error {
return nil return nil
} }
// chromeOSVMRange is the subset of the CGNAT IPv4 range used by
// ChromeOS to interconnect the host OS to containers and VMs. We
// avoid allocating Tailscale IPs from it, to avoid conflicts.
const chromeOSVMRange = "100.115.92.0/23"
// addBaseNetfilter4 installs the basic IPv4 netfilter framework for // addBaseNetfilter4 installs the basic IPv4 netfilter framework for
// Tailscale, in preparation for inserting more rules later. // Tailscale, in preparation for inserting more rules later.
func (r *linuxRouter) addBaseNetfilter4() error { func (r *linuxRouter) addBaseNetfilter4() error {
@ -559,7 +559,7 @@ func (r *linuxRouter) addBaseNetfilter4() error {
// //
// Note, this will definitely break nodes that end up using the // Note, this will definitely break nodes that end up using the
// CGNAT range for other purposes :(. // CGNAT range for other purposes :(.
if err := r.ipt4.Append("filter", "ts-input", "!", "-i", r.tunname, "-s", "100.115.92.0/23", "-m", "comment", "--comment", "ChromeOS special ranges", "-j", "RETURN"); err != nil { if err := r.ipt4.Append("filter", "ts-input", "!", "-i", r.tunname, "-s", chromeOSVMRange, "-m", "comment", "--comment", "ChromeOS VM connectivity", "-j", "RETURN"); err != nil {
return err return err
} }
if err := r.ipt4.Append("filter", "ts-input", "!", "-i", r.tunname, "-s", "100.64.0.0/10", "-j", "DROP"); err != nil { if err := r.ipt4.Append("filter", "ts-input", "!", "-i", r.tunname, "-s", "100.64.0.0/10", "-j", "DROP"); err != nil {
@ -571,6 +571,14 @@ func (r *linuxRouter) addBaseNetfilter4() error {
// filter/FORWARD later on. We use packet marks here so both // filter/FORWARD later on. We use packet marks here so both
// filter/FORWARD and nat/POSTROUTING can match on these packets // filter/FORWARD and nat/POSTROUTING can match on these packets
// of interest. // of interest.
//
// In particular, we only want to apply masquerading in
// nat/POSTROUTING to packets that originated from the Tailscale
// interface, but we can't match on the inbound interface in
// POSTROUTING. So instead, we match on the inbound interface and
// destination IP in filter/FORWARD, and set a packet mark that
// nat/POSTROUTING can use to effectively run that same test
// again.
if err := r.ipt4.Append("filter", "ts-forward", "-m", "mark", "--mark", tailscaleSubnetRouteMark, "-j", "ACCEPT"); err != nil { if err := r.ipt4.Append("filter", "ts-forward", "-m", "mark", "--mark", tailscaleSubnetRouteMark, "-j", "ACCEPT"); err != nil {
return err return err
} }