This section didn't mention the effect of the --map-host-loopback option which now alters this behaviour. Update it accordingly. It used "local addresses" to mean specifically 127.0.0.0/8 and ::1. However, "local" could also refer to link-local addresses or to addresses of any scope which happen to be configured on the host. Use "loopback address" to be more precise about this. Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- passt.1 | 54 ++++++++++++++++++++++++++++-------------------------- 1 file changed, 28 insertions(+), 26 deletions(-) diff --git a/passt.1 b/passt.1 index acc1f92..11104e1 100644 --- a/passt.1 +++ b/passt.1 @@ -863,38 +863,40 @@ root@localhost's password: .SH NOTES -.SS Handling of traffic with local destination and source addresses - -Both \fBpasst\fR and \fBpasta\fR can bind on ports with a local address, -depending on the configuration. Local destination or source addresses need to be -changed before packets are delivered to the guest or target namespace: most -operating systems would drop packets received from non-loopback interfaces with -local addresses, and it would also be impossible for guest or target namespace -to route answers back. - -For convenience, and somewhat arbitrarily, the source address on these packets -is translated to the address of the default IPv4 or IPv6 gateway (if any) -- -this is known to be an existing, valid address on the same subnet. - -Loopback destination addresses are instead translated to the observed external -address of the guest or target namespace. For IPv6 packets, if usage of a -link-local address by guest or namespace has ever been observed, and the -original destination address is also a link-local address, the observed -link-local address is used. Otherwise, the observed global address is used. For -both IPv4 and IPv6, if no addresses have been seen yet, the configured addresses -will be used instead. +.SS Handling of traffic with loopback destination and source addresses + +Both \fBpasst\fR and \fBpasta\fR can bind on ports with a loopback +address (127.0.0.0/8 or ::1), depending on the configuration. Loopback +destination or source addresses need to be changed before packets are +delivered to the guest or target namespace: most operating systems +would drop packets received with loopback addresses on non-loopback +interfaces, and it would also be impossible for guest or target +namespace to route answers back. + +For convenience, the source address on these packets is translated to +the address specified by the \fB\-\-map-host-loopback\fR option. If +not specified this defaults, somewhat arbitrarily, to the address of +default IPv4 or IPv6 gateway (if any) -- this is known to be an +existing, valid address on the same subnet. If \fB\-\-no-map-gw\fR or +\fB\-\-map-host-loopback none\fR are specified this translation is +disabled and packets with loopback addresses are simply dropped. + +Loopback destination addresses are translated to the observed external +address of the guest or target namespace. For IPv6, the observed +link-local address is used if the translated source address is +link-local, otherwise the observed global address is used. For both +IPv4 and IPv6, if no addresses have been seen yet, the configured +addresses will be used instead. For example, if \fBpasst\fR or \fBpasta\fR receive a connection from 127.0.0.1, with destination 127.0.0.10, and the default IPv4 gateway is 192.0.2.1, while the last observed source address from guest or namespace is 192.0.2.2, this will be translated to a connection from 192.0.2.1 to 192.0.2.2. -Similarly, for traffic coming from guest or namespace, packets with destination -address corresponding to the default gateway will have their destination address -translated to a loopback address, if and only if a packet, in the opposite -direction, with a loopback destination or source address, port-wise matching for -UDP, or connection-wise for TCP, has been recently forwarded to guest or -namespace. This behaviour can be disabled with \-\-no\-map\-gw. +Similarly, for traffic coming from guest or namespace, packets with +destination address corresponding to the \fB\-\-map-host-loopback\fR +address will have their destination address translated to a loopback +address. .SS Handling of local traffic in pasta -- 2.46.2