debian 10, vm cant connect to the host bridge

Thomas Luening toml at thlu.de
Mon Sep 7 16:36:44 UTC 2020 

Hi

Am 07.09.20 um 12:49 schrieb Schuldei, Andreas:
> someone recommended that i should give br0 the same hardware address as eno2.

Not in all cases. The example attached in the quotation below looks a little bit confused.... there is more then one Bridge.

If I create an isolated guest-network with "virsh net-start default", i.e. with NAT/netfilter and DHCP/dnsmasq, it looks like 
the following example... the virtual MAC addresses are not identical to eth0.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP group default qlen 1000
     link/ether d0:50:12:34:56:78 brd ff:ff:ff:ff:ff:ff
10: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
     link/ether 52:54:00:0a:cd:21 brd ff:ff:ff:ff:ff:ff
     inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
        valid_lft forever preferred_lft forever
11: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000
     link/ether 52:54:00:0a:cd:21 brd ff:ff:ff:ff:ff:ff

If I set up the VM as an integrated LAN-Client, 'virbr0-nic' is not necessary, because the virtual NICs are connected directly 
to br0 as master. Then it looks different with the MACs, the virtual interface for the running VM has its own MAC and the VM 
itself can receive a regulare LAN-IP from LAN-DHCP-Server, e.g. from DSL-Router in private.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP group default qlen 1000
     link/ether d0:50:12:34:56:78 brd ff:ff:ff:ff:ff:ff
12: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
     link/ether d0:50:12:34:56:78 brd ff:ff:ff:ff:ff:ff
     inet 10.0.1.20/24 brd 10.10.1.255 scope global dynamic br0
        valid_lft 862367sec preferred_lft 862367sec
13: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UNKNOWN group default qlen 1000
     link/ether fe:54:00:e6:57:ff brd ff:ff:ff:ff:ff:ff

Imho you have to differentiate, whether the VM is running in an isolated network or the VM is running as a regular LAN client.

HTH & BR, Tom



> ip a
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
>      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>      inet 127.0.0.1/8 scope host lo
>         valid_lft forever preferred_lft forever
>      inet6 ::1/128 scope host
>         valid_lft forever preferred_lft forever
> 2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
>      link/ether 34:48:ed:f0:a9:e8 brd ff:ff:ff:ff:ff:ff
>      inet 10.12.0.13/24 brd 10.12.0.255 scope global eno1
>         valid_lft forever preferred_lft forever
>      inet6 fe80::3648:edff:fef0:a9e8/64 scope link
>         valid_lft forever preferred_lft forever
> 3: eno2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master br0 state UP group default qlen 1000
>      link/ether 34:48:ed:f0:a9:e9 brd ff:ff:ff:ff:ff:ff
>      inet6 fe80::3648:edff:fef0:a9e9/64 scope link
>         valid_lft forever preferred_lft forever
> 4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
>      link/ether 34:48:ed:f0:a9:e9 brd ff:ff:ff:ff:ff:ff
>      inet6 fe80::e467:7bff:fe87:b5ca/64 scope link
>         valid_lft forever preferred_lft forever
> 5: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
>      link/ether 52:54:00:2b:e3:f7 brd ff:ff:ff:ff:ff:ff
>      inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
>         valid_lft forever preferred_lft forever
> 6: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000
>      link/ether 52:54:00:2b:e3:f7 brd ff:ff:ff:ff:ff:ff
> 20: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UNKNOWN group default qlen 1000
>      link/ether fe:54:00:29:b6:e0 brd ff:ff:ff:ff:ff:ff
>      inet6 fe80::fc54:ff:fe29:b6e0/64 scope link
>         valid_lft forever preferred_lft forever

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