[CentOS-virt] xen setup documentation for centos?

lee lee at yun.yagibdah.de
Fri Jun 6 03:23:10 UTC 2014


George Dunlap <dunlapg at umich.edu> writes:

> *I* care about the documentation that didn't work, so that other
> people don't trip over the same thing.  :-)  If you've walked this
> path and become frustrated, there are probably a dozen other people
> who have also walked it and just not said anything.

To give an example:

https://www.centos.org/docs/5/html/5.1/Deployment_Guide/s1-networkscripts-static-routes.html


[root at charon ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
BOOTPROTO=none
DNS1="192.168.178.20"
IPADDR="192.168.1.1"
NETMASK="255.255.255.255"
NM_CONTROLLED=no
ONBOOT="yes"
TYPE="Ethernet"
UUID="1b645d25-9f66-4335-ba0b-939cdd9f553f"

[root at charon ~]# cat /etc/sysconfig/network-scripts/route-eth0 
192.168.178.0/24 via 192.168.1.1 eth0
default 192.168.178.200 dev eth0

[root at charon ~]# service network restart
Shutting down interface eth0:  [  OK  ]
Shutting down loopback interface:  [  OK  ]
Bringing up loopback interface:  [  OK  ]
Bringing up interface eth0:  Determining if ip address 192.168.1.1 is already in use for device eth0...
Error: either "to" is duplicate, or "eth0" is a garbage.
Error: either "to" is duplicate, or "192.168.178.200" is a garbage.
[  OK  ]
[root at charon ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
[root at charon ~]# 


https://docs.fedoraproject.org/en-US/Fedora/13/html/Deployment_Guide/s1-networkscripts-static-routes.html

"If the default gateway is already assigned from DHCP, the IP command
arguments format can cause one of two errors during start-up, or when
bringing up an interface from the down state using the ifup command:
"RTNETLINK answers: File exists" or 'Error: either "to" is a duplicate,
or "X.X.X.X" is a garbage.', where X.X.X.X is the gateway, or a
different IP address. These errors can also occur if you have another
route to another network using the default gateway. Both of these errors
are safe to ignore."


This error is not "save to ignore" because it makes the network
unreachable.  Without the duplication and only the default route
specified, I`m getting the same error, though only once, and still no
routing.

Then from
https://docs.fedoraproject.org/en-US/Fedora/13/html/Deployment_Guide/s1-networkscripts-static-routes.html:


"You can also use the network/netmask directives format for
route-interface files. The following is a template for the
network/netmask format, with instructions following afterwards:
[...]"


Let`s see ...


[root at charon ~]# cat /etc/sysconfig/network-scripts/route-eth0 
ADDRESS0=192.168.178.0
NETMASK0=255.255.255.0
GATEWAY0=192.168.1.1

[root at charon ~]# service network restart
Shutting down interface eth0:  [  OK  ]
Shutting down loopback interface:  [  OK  ]
Bringing up loopback interface:  [  OK  ]
Bringing up interface eth0:  Determining if ip address 192.168.1.1 is already in use for device eth0...
[  OK  ]
[root at charon ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.178.0   192.168.1.1     255.255.255.0   UG    0      0        0 eth0
[root at charon ~]# 


So why does the second approach work and the first one doesn`t?  It
looks still strange since eth0 is configured with 192.168.1.1 anyway ---
but perhaps it`s ok since there are two more interfaces.

Figuring this out was even fast; it took less than an hour.  Other
things take hours over hours, and it goes on and on like this.


For some things, there isn`t even any documentation I could find, like
how to make sure that virtual interfaces in dom0 have consistent names
and that such interfaces are consistently connected to particular
interfaces in particular domUs:

For firewalling and routing, I require a domU with three virtual
interfaces and access to a physical one.  Obviously, the names of the
interfaces must remain consistent rather than change all the time.
Otherwise it will be impossible to get the networking for all the guests
sorted out.

Like in the above example: How do I make sure that eth0 of the guest
will always be connected to a particular bridge and show up as a
particular interface in dom0?  It`s going to be the interface to the DMZ
--- you can imagine what would happen if that interface suddenly shows
up as the bridge guests in the LAN will be connected to ...


-- 
Knowledge is volatile and fluid.  Software is power.


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