As a vCMP^® host administrator, when you create or modify a guest, you typically publish one or more host-based VLANs to the guest. When you publish a host-based VLAN to a guest, you are granting a subscription to the guest for use of that VLAN configuration, with the VLAN's underlying Layer 2 resources.

When you publish a VLAN to a guest, if there is no existing VLAN within the guest with the same name or tag as the host-based VLAN, the vCMP system automatically creates, on the guest, a configuration for the published VLAN.

If you modify a guest's properties to remove a VLAN publication from a guest, you are removing the guest's subscription to that host-based VLAN. However, the actual VLAN configuration that the host created within the guest during initial VLAN publication to the guest remains there for the guest to use. In this case, any changes that a host administrator might make to that VLAN are not propagated to the guest.

In general, VLANs that appear within a guest can be either host-based VLANs currently published to the guest, host-based VLANs that were once but are no longer published to the guest, or VLANs that the guest administrator manually created within the guest.

This example shows the effect of publishing a host-based VLAN to, and then deleting the VLAN publication from, a guest that initially had no VLANs.

# Within guest G1, show that the guest has no VLANs configured:
 
[root@G1:/S1-green-P:Active:Standalone] config # tmsh list net vlan   

# From the host, publish VLAN v1024 to guest G1:
 
[root@host_210:/S1-green-P:Active:Standalone] config # tmsh modify vcmp guest G1 vlans add { v1024 }

# Within guest G1, list all VLANs:
 
[root@G1:/S1-green-P:Active:Standalone] config # tmsh list net vlan
 
                     net vlan v1024 {
if-index 96
tag 1024
}

# On the host, delete the host-based VLAN publication from guest G1:    

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh modify vcmp guest G1 vlans del { v1024 } 

# Notice that the host-based VLAN still exists within the guest:

[root@G1:/S1-green-P:Active:Standalone] config # tmsh list net vlan

                     vlan v1024 {
if-index 96
tag 1024
}
                  

Sometimes a host administrator might publish a VLAN to a guest, but the guest administrator has already created, or later creates, a VLAN with a different name but the same VLAN tag. In this case, the guest VLAN always overrides the host VLAN. The VLAN can still exist on the host (for other guests to subscribe to), but it is the guest VLAN that is used.

Whenever host and guest VLANs have different names but the same tags, traffic flows successfully across the host from the guest because the VLAN tag alignment is correct. That is, when the tags match, the underlying Layer 2 infrastructure of the VLANs matches, thereby enabling the host to reach the guest.

The example here shows the tmsh command sequence for creating two separate VLANs with different names and the same tag, and the resulting successful traffic flow.

# On the host, create a VLAN with a unique name but with a tag matching that of a guest VLAN VLAN_A:
   
[root@host_210:/S1-green-P:Active:Standalone] config # tmsh create net vlan VLAN_B tag 1000
                     

# On the host, publish the host VLAN to the guest:

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh modify vcmp guest guest1 vlans add { VLAN_B }

# Within the guest, show that the guest still has its own VLAN only, and not the VLAN published from the host:

[root@G1:/S1-green-P:Active:Standalone] config # tmsh list net vlan all
   
                     net vlan VLAN_A {
    if-index 192
    tag 1000
    }

# On the guest, create a self IP address for VLAN_A:

[root@G1:/S1-green-P:Active:Standalone] config # tmsh create net self 10.1.1.1/24 vlan VLAN_A
   
# On the host, delete the self IP address on VLAN_A (this VLAN also exists on the guest) and re-create the self IP address on VLAN_B (this VLAN has the same tag as VLAN_A):

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh delete net self 10.1.1.2/24
[root@host_210:/S1-green-P:Active:Standalone] config # tmsh create net self 10.1.1.2/24 vlan VLAN_B

# From the host, open a connection to the guest, and notice that because the two VLANs have the same tags, the connection suceeds:

[root@host_210:/S1-green-P:Active:Standalone] config # ping -c2 10.1.1.1
   
                     PING 10.1.1.1 (10.1.1.1) 56(84) bytes of data.
64 bytes from 10.1.1.1: icmp_seq=1 ttl=255 time=3.35 ms
64 bytes from 10.1.1.1: icmp_seq=2 ttl=255 time=0.989 ms

--- 10.1.1.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.989/2.170/3.352/1.182 ms
                  

Sometimes a host administrator might publish a VLAN to a guest, but the guest administrator has already created, or later creates, a VLAN with the same name but with a different VLAN tag. In this case, the guest VLAN always overrides the host VLAN. The VLAN can still exist on the host (for other guests to subscribe to), but it is the guest VLAN that is used.

Whenever host and guest VLANs have the same names but different tags, traffic cannot flow between the identically-named VLANs at Layer 2. That is, when the tags do not match, the underlying Layer 2 infrastructure of the VLANs does not match, thereby preventing the host from reaching the guest.

The example here shows the tmsh command sequence for creating two separate VLANs with the same names and different tags, and the resulting traffic flow issue.

# While logged into the guest, create a VLAN:
   
[root@G1:/S1-green-P:Active:Standalone] config # tmsh create net vlan VLAN_A tag 1000
                     

# Show that no VLANs exist on the host:

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh list net vlan all 
[root@host_210:/S1-green-P:Active:Standalone] config # 

# On the host, create a VLAN with the same name as the guest VLAN but with a unique tag on the host:

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh create net vlan VLAN_A tag 1001
                     

# Publish the host VLAN to the guest:

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh modify vcmp guest guest1 vlans add { VLAN_A }

# Within the guest, show that the guest still has its own VLAN only, and not the VLAN published from the host:

[root@G1:/S1-green-P:Active:Standalone] config # tmsh list net vlan all

                     net vlan VLAN_A {
    if-index 192
    tag 1000
    }
 
# Within the guest, create a self IP address for the VLAN:

[root@G1:/S1-green-P:Active:Standalone] config # tmsh create net self 10.1.1.1/24 vlan VLAN_A
                     

# On the host, create a self IP address for the identically-named VLAN:

[root@host_210:/S1-green-P:Active:Standalone] config # tmsh create net self 10.1.1.2/24 vlan VLAN_A
                     

# From the host, open a connection to the guest, and notice that because the two VLANs have different tags, the connection fails:

[root@host_210:/S1-green-P:Active:Standalone] config # ping -c2 10.1.1.1
   
                     PING 10.1.1.1 (10.1.1.1) 56(84) bytes of data.
From 10.1.1.2 icmp_seq=1 Destination Host Unreachable
From 10.1.1.2 icmp_seq=2 Destination Host Unreachable

--- 10.1.1.1 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 3000ms
pipe 2 
                  

When a host-based VLAN and a guest-created VLAN have identical names but different VLAN tags, traffic flow at Layer 2 is impeded between host and guest. Fortunately, you can resolve this issue by performing these tasks, in the sequence shown:

• Within the guest, delete the relevant VLAN from within the guest.
• On the host, remove the VLAN publication from the guest.
• On the host, modify the tag of the host-based VLAN.
• On the host, publish the VLAN to the guest.
• Within the guest, view the VLAN from within the guest.