Re: About bridges

[Jason Mitchell <jmitchel%bigjar.com@localhost>]

On 5/30/21 11:29 AM, Robert Swindells wrote:
> Staffan Thomén <staffan%shangtai.net@localhost> wrote:
> > Robert Swindells wrote:
> > > Staffan Thomén<staffan%shangtai.net@localhost>  wrote:
> > > > No takers for this? Can someone at least check that I'm not crazy?
> > > Which bit of "this" ?
> > >
> > > Your last message suggests to me that you have a working bridged network.
> > It works partially; DHCP replies don't seem to show up on the tap device
> > so it does not configure an address. I kept a tcpdump on the tap while
> > running dhcpcd and I can see dhcpcd retrying the sending to no avail.
> Do you need to use DHCP to get an address ?
>
> I have a theory that the MAC address learning feature of bridge(4)
> doesn't work well with BOOTP/DHCP, I have a local change to explicitly
> add the MAC address of each interface. You could look at the state of
> the address cache by running 'brconfig -a'.
>
> People use tap(4) in two ways:
>
> 1) To add an extra IP address for the host machine.
> 2) To connect a software emulator like qemu to the host.
>
> In usage 2, you don't setup an IP address for the tap(4) device, the
> virtual network device in the emulator has a different MAC address to
> the tap(4) device and can get an IP address using DHCP.
>
> Also, there is a shortcut in bridge(4) if it detects that a packet is
> for an "internal" address.
>
> If you do add an IP address for the tap(4) device then that will be
> treated as an internal one.
>
> > Additionally, even if I manually configure an address on the tap
> > interface and I can use it to connect using ssh, tcpdump on the tap
> > device doesn't show the unicast packets, which I don't think is right
> > either.
> I think that usage will be hitting the shortcut I described above, the
> packets are treated as being for the host machine so don't get sent to
> the tap interface.
Okay, I got this working with a wired interface but only by adding an IP 
address to the physical nic (in my case axe0). The address wasn't in the 
same subnet as the address for tap1 (I used 169.254.169.254). Here are 
my commands (below). At some point I'll try to get DHCP up and running.

HTH,

Jason M.

--------------------------------------------

root@ARMNUK:/# ifconfig -a
awge0: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ec_capabilities=1<VLAN_MTU>
        ec_enabled=0
        address: 00:1e:06:37:45:a1
        media: Ethernet autoselect (100baseTX full-duplex)
        status: active
        inet6 fe80::21e:6ff:fe37:45a1%awge0/64 flags 0x0 scopeid 0x1
        inet A.B.C.12/24 broadcast A.B.C.255 flags 0x0
axe0: flags=0x8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500
        ec_capabilities=1<VLAN_MTU>
        ec_enabled=0
        address: 00:90:9e:9a:b1:05
        media: Ethernet autoselect (100baseTX full-duplex)
        status: active
lo0: flags=0x8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33624
        inet6 ::1/128 flags 0x20<NODAD>
        inet6 fe80::1%lo0/64 flags 0x0 scopeid 0x3
        inet 127.0.0.1/16 flags 0x0
lo1: flags=0x8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33624
        inet6 ::1/128 flags 0x20<NODAD>
        inet6 fe80::1%lo1/64 flags 0x0 scopeid 0x4
        inet 127.0.1.1/24 flags 0x0
tap1: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ec_capabilities=5<VLAN_MTU,JUMBO_MTU>
        ec_enabled=0
        address: f2:0b:a4:7c:28:e4
        media: Ethernet autoselect
        inet6 fe80::f00b:a4ff:fe7c:28e4%tap1/64 flags 0x0 scopeid 0x5
        inet 127.0.2.1/24 broadcast 127.0.2.255 flags 0x0
root@ARMNUK:/# ifconfig bridge0 create up
root@ARMNUK:/# ifconfig tap1 A.B.C.254/24
root@ARMNUK:/# brconfig bridge0 add tap1 add axe0 stp
brconfig: command stp requires 1 argument
root@ARMNUK:/# brconfig bridge0 add tap1 add stp axe0
brconfig: add tap1: File exists
root@ARMNUK:/# brconfig -a
bridge0: flags=41<UP,RUNNING>
        Configuration:
                priority 32768 hellotime 2 fwddelay 15 maxage 20
                ipfilter disabled flags 0x0
        Interfaces:
                axe0 flags=3<LEARNING,DISCOVER>
                        port 2 priority 128
                tap1 flags=3<LEARNING,DISCOVER>
                        port 5 priority 128
        Address cache (max cache: 100, timeout: 1200):
root@ARMNUK:/# ifconfig axe0 169.254.169.254
root@ARMNUK:/# #Pings get answered 4 seconds after this.
root@ARMNUK:/#
root@ARMNUK:/# brconfig -a
bridge0: flags=41<UP,RUNNING>
        Configuration:
                priority 32768 hellotime 2 fwddelay 15 maxage 20
                ipfilter disabled flags 0x0
        Interfaces:
                axe0 flags=3<LEARNING,DISCOVER>
                        port 2 priority 128
                tap1 flags=3<LEARNING,DISCOVER>
                        port 5 priority 128
        Address cache (max cache: 100, timeout: 1200):
                3c:22:fb:00:45:67 axe0 1091 flags=0<>
                a2:00:61:fc:f0:fa axe0 1194 flags=0<>
                54:4a:00:b8:4b:21 axe0 1199 flags=0<>
                00:1e:06:37:45:a1 axe0 1058 flags=0<>
                a0:ce:c8:00:00:29 axe0 1199 flags=0<>
                54:4a:00:b8:4b:20 axe0 1194 flags=0<>