CHARON-VAX for Linux virtual network

Conventions

Throughout the document(s) these conventions are followed

Notation	Description
$	The dollar sign in interactive examples indicates an operating system prompt for VMS. The dollar sign can also indicate non superuser prompt for UNIX / Linux.
#	The number sign represents the superuser prompt for UNIX / Linux.
>	The right angle bracket in interactive examples indicates an operating system prompt for Windows command (cmd.exe).
`User input`	Bold monospace type in interactive examples indicates typed user input.
`<path>`	Bold monospace type enclosed by angle brackets indicates command parameters and parameter values.
`Output`	Monospace type in interactive examples, indicates command response output.
[ ]	In syntax definitions, brackets indicate items that are optional.
...	In syntax definitions, a horizontal ellipsis indicates that the preceding item can be repeated one or more times.
`dsk0`	Italic monospace type, in interactive examples, indicates typed context dependent user input.

The following definitions apply

Term	Description
Host	The system on which the emulator runs, also called the Charon server
Guest	The operating system running on a Charon instance, for example, Tru64 UNIX, OpenVMS, Solaris, MPE or HP-UX

Back to Table of Contents

General description

It is strongly recommended to use only physical network adapters for CHARON-VAX networking to gain maximum performance. In situations where the host has only one network adapter, you can use the LINUX virtual network Interfaces ("TUN/TAP") and map individual CHARON-VAX instances to their own virtual interfaces.

There are 2 ways to create the LINUX virtual network Interfaces ("TUN/TAP"):

Using "ncu" utility
Manually

Back to Table of Contents

Using "ncu" utility to establish CHARON virtual network

Login a root. Start "ncu" utility:

# ncu
CHARON Network Configuration Utility, STROMASYS (c) 2014

Interfaces Dedicated to State
---------- ------------ ------------
eth0 host         connected to host
eth1       host         connected to host
lo         host         unmanaged to host
select action:
D - Dedicate to CHARON
R - Release to host
B - Create Bridge with TAPs
C - Destroy Bridge
S - Print status
E - Exit
:> B

Enter "B" or "b" to create a bridge between the host physical network adapter and the LINUX virtual network Interfaces (TAP) and specify the physical network interface ("eth1" in our example) and a number of the virtual network Interfaces to be created (2 in our example):

Specify the interface to be used for BRIDGE:eth1
How many tap should be created:2
grep: /etc/ncu_br.cfg: No such file or directory
Cannot change rx-checksumming
Could not change any device features
Actual changes:
tx-checksumming: off
tx-checksum-ip-generic: off
tcp-segmentation-offload: off
tx-tcp-segmentation: off [requested on]
tx-tcp-ecn-segmentation: off [requested on]
tx-tcp6-segmentation: off [requested on]
udp-fragmentation-offload: off [requested on]
Actual changes:
scatter-gather: off
tx-scatter-gather: off
tx-scatter-gather-fraglist: off
generic-segmentation-offload: off [requested on]
Cannot change tx-vlan-offload
Cannot change rx-vlan-offload
Binding bridge to eth1...
br0_eth1 Route[] eth0
Forming the bridge: ..1..2..3..4..5.. addif tap0 .. addif tap1 ..7..8 done!
Formed bridge br0_eth1 attached over eth1...

select action:
D - Dedicate to CHARON
R - Release to host
B - Create Bridge with TAPs
C - Destroy Bridge
S - Print status
E - Exit
:> S

Now enter "S" or "s" to see the created virtual interfaces:

Interfaces Dedicated to State
---------- ------------ ------------
eth0       host         connected to host
eth1       bridge       connected to bridge
lo         host         unmanaged to host
tap0       bridge       unmanaged to bridge
tap1       bridge       unmanaged to bridge

select action:
D - Dedicate to CHARON
R - Release to host
B - Create Bridge with TAPs
C - Destroy Bridge
S - Print status
E - Exit
:> E

In the example above we see 2 virtual network Interfaces "tap0" and "tap1" connected to the created bridge. The physical network interface "eth1" is used for the bridge to the virtual network interfaces.

The interfaces "tap0" and "tap1" are ready to be used in CHARON configurations - they do not need to be additionally dedicated to CHARON.

Enter "E" or "e" to quit "ncu" utility.

Back to Table of Contents

Manual configuration of CHARON virtual network

Preparation of the host to create the virtual network

Login as "root" user.
Configure the physical network interface to run in promiscuous mode using the following command. This interface will be dedicated to the whole network bridge (created later).
# ifconfig eth<N> 0.0.0.0 promisc up
Promiscuous mode allows the physical (or virtual) network interface to accept the entire volume of incoming packets. This mode is essential for consistency of the information transfer.
In case the firewall is enabled on the host system, the following command should be executed to allow the bridge to forward IP packets:
# /sbin/iptable -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT
This command can also be performed from the bridge configuration script. It has to be executed each time the iptables service is (re)started.
It is also possible to make this setting system-wide. Either:
1. Issue the given command from the firewall control panel.
2. Add the following line to the end of the "/etc/sysconfig/iptables" file:
  -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT

Back to Table of Contents

Virtual interface creation

Creation of the desired number of virtual network interfaces (TAPs) can be performed in the following way:

# tunctl [-t tap<N>]

where “tap<N>” is a name of an instance of the virtual network interface, i.e. “tap0”, “tap1” etc.

Once each virtual network interface instance is created it must be set to promiscuous mode:

# /sbin/ifconfig tap<N> promisc up

Back to Table of Contents

Bridge creation

To interconnect the physical and virtual network interfaces created in the previous step the network bridge must be introduced in the following way:

# /usr/sbin/brctl addbr br0

where “br0” stands for a name of the created bridge.

Now it is possible to add the network interfaces to the created bridge:

# /usr/sbin/brctl addif br0 eth<N> # /usr/sbin/brctl addif br0 tap0 … # /usr/sbin/brctl addif br0 tap<N>

Example:

# /usr/sbin/brctl addif br0 eth1

# /usr/sbin/brctl addif br0 tap0

The proposed configuration assumes one and only one network bridge, so loops are not possible. It is required to turn off the spanning tree protocol with the following command:

# /usr/sbin/brctl stp br0 off

Back to Table of Contents

Starting bridge

To start the created bridge “br0” use the following command:

# /sbin/ifconfig br0 up

Back to Table of Contents

Usage of the virtual interface in CHARON-VAX configuration

Once the “tap<N>” interfaces have been created, the load command maps those interfaces to CHARON-VAX:

... load tap_port/chnetwrk XQA0 interface="tap<N>"
...

Back to Table of Contents