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

From: peter
Subject: Re: Connection of a qemu guest to the 'net.
Date: Wed, 17 Mar 2021 11:05:34 -0700

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

A very helpful essay, thanks.  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 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) Will try to reproduce your scenario 1. Therefore attempt to set up 
br0 is with these lines in /etc/crontab.

@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
6: br0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen
    link/ether 12:d0:83:de:71:f5 brd ff:ff:ff:ff:ff:ff

So br0 was created.  Appears "ip link set br0 up" and following ip 
commands failed.  Any ideas about that?

Thanks,              ... P.

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

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