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Why can the VIO Client network interface communicate with the default gateway, but the VIO Server network interface cannot?

Question & Answer


Question

Why can the VIO Client network interface communicate with the default gateway, but the VIO Server network interface cannot?
Setup:
AIX: 7300-02-01-2346
VIOS: 3.1.4.21
Model: 9106-22B (Power10)
Firmware: 1030.30
image-20250423140606-1

Answer

In current configuration, packets need to have VLAN ID of 480 to communicate with gateway. Figure 1 shows how network packets traverse from the VIO Client interface en0 to the gateway in the current configuration.
(1) The packet without VLAN ID is transmitted by en0.
(2) The VLAN ID 480 is added to as packet goes through port P1.
(3) The VLAN ID 480 left intact as packet goes through port P2.
(4) The VLAN ID 480 left intact as packet goes through port S1.
(5) The VLAN ID 480 is removed as packet goes though port S2 and received by the gateway.

image-20250423211143-1

Figure 2 shows how network packets traverse from the VIOS Server interface en2 to the gateway in the current configuration.

(1) The packet without VLAN ID is transmitted by en2/ent2.
(2) The VLAN ID 999 is added as packet goes through port S1. 
(3) The packet is dropped by port S2 because it does not have VLAN ID 480.
image-20250423141208-3

The packets are dropped because they do not have VLAN ID 480. The VIO server must send packets with VLAN ID 480 in order for it to be able to communicate with a gateway. There are two solutions to resolve this problem. Only one solution is needed. (A) Create a VLAN Adapter with vlan_tag_id 480 on top of SEA (B) Create a Virtual Ethernet Adapter (VEA) with PVID 480.  

(A) Create a VLAN adapter with base adapter ent2 and VLAN ID 480, then configure the IP address on the VLAN adapter interface. 

► On VIO Server, as a root from HMC console session:

- ifconfig en2 down;ifconfig en2 detach
- rmdev -dl en2
- mkdev -c adapter -s vlan -t eth -a base_adapter='ent2' -a 'vlan_tag_id='480' -a vlan_priority='0'
  This will create a VLAN adapter ent3.
- cfgmgr

- configure IP address on en3.

After changes are done successfully, Figure 3 shows how network packets traverse from the VIO Server network interface en3 to the gateway.

(1) The packet with VLAN ID 480 is transmitted by en3/ent3.
(2) The packet left intact as it goes through SEA ent2.
(3) The VLAN ID 480 left intact as packet goes through port S1.
(4) The VLAN ID 480 is removed as packet goes through port S2 and received by the gateway.
image-20250423211328-2

(B) Create a Virtual Ethernet Adapter (VEA) with PVID 480, then configure the IP address on the VEA interface. 

► On VIO Server, as a root using HMC console session:

- ifconfig en2 down;ifconfig en2 detach
- rmdev -dl en2
- cfgmgr

► On HMC CLI, as a hscroot:

chhwres -r virtualio -m <name of the managed system> -o a -p <name of the VIO Server> --rsubtype eth -a "port_vlan_id=480,vswitch=ETHERNET0,ieee_virtual_eth=0"

Note: setup uses default vswitch ETHERNET0.

► On VIO Server, as a root using HMC console session:

- cfgmgr
  This will create a new VEA ent3 with PVID 480 and VLAN ID none.
- configure IP address on en3
After changes are done successfully, Figure 4 shows how network packets traverse from the VIO Server network interface en3 to the gateway.
(1) The packet without VLAN ID is transmitted by en3.
(2) The VLAN ID 480 is added to as packet goes through port P3.
(3) The VLAN ID 480 left intact as packet goes through port P2.
(4) The VLAN ID 480 left intact as packet goes through port S1.
(5) The VLAN ID 480 is removed as packet goes though port S2 and received by the gateway.
image-20250423211724-1

In summary, it is important to tag the packets with the correct VLAN ID based on the destination host's VLAN ID and switch port configuration. If packets do not have the correct VLAN ID, then they will be dropped.

Author: Darshan Patel, Ivonne Barrantes
Platform: AIX and VIOS on Power

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Document Information

Modified date:
24 April 2025

UID

ibm17230820

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