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Correction: Re: Connection of a qemu guest to the 'net.

From: peter
Subject: Correction: Re: Connection of a qemu guest to the 'net.
Date: Wed, 17 Mar 2021 12:45:03 -0700

br0 received addresses here.

> This is a long email. In answering your question I got on a roll and 
ended up writing an essay. 

A very helpful essay.  I wonder whether you might incorporate it into 
the QEMU wikibook.  

I need to hypothesize some comments and ask some questions.
Contradiction of errors welcome.

(1) Bridging is at the OSI Data Link layer.  Interfaces and IP 
addresses are at the OSI Network layer; immediately above the Data 
Link.  Hence the requirement to create and configure a bridge before 
connecting an interface to it.

(2) A LAN works here, with Shorewall being the most prominent 
ingredient. No bridge is evident but a subnetted machine can access 
Web pages on the 'net. Given (1) I am puzzled how that is possible 
with no bridge.

(3) I'll try to reproduce your scenario 1. Therefore these lines in 

@reboot root ip link add br0 type bridge
@reboot root ip link set br0 up
@reboot root ip addr add dev br0
@reboot root ip addr add fd99:9999:9999:9999::1 dev br0

(4) Check the result.

root@joule:~# ip addr show dev br0
5: br0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen
    link/ether ce:bf:79:6f:19:e4 brd ff:ff:ff:ff:ff:ff

So br0 was created.  Appears "ip link set br0 up" and following ip 
commands failed.  

If the last three lines are removed from /etc/crontab and this 
is added to /etc/network/interfaces, progress is better.

# Bridge to connect qemu guest.
auto br0
iface br0 inet static

iface br0 inet6 static
        address fd99:9999:9999:9999::1/64
This is the result.

6: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN g
roup default qlen 1000
    link/ether 6e:05:fd:df:e2:eb brd ff:ff:ff:ff:ff:ff
    inet brd scope global br0
       valid_lft forever preferred_lft forever
    inet6 fd99:9999:9999:9999::1/64 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::6c05:fdff:fedf:e2eb/64 scope link
       valid_lft forever preferred_lft forever

I don't understand how the second inet6 address is derived. 

Thanks,              ... P.

cell: +1 236 464 1479            Bcc: peter at easthope. ca
VoIP: +1 604 670 0140

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