Figure 3-14 Networking diagram of Layer 3 communications between a sub-VLAN and
an external network
RouterA
VLAN 3VLAN 2
Super VLAN 4
VLANIF4:10.1.1.1/24
Host A
10.1.1.2/24
Host B
10.1.1.3/24
Eth2/0/1 Eth2/0/2
RouterB
Eth2/0/3
Eth2/0/1
VLANIF10
10.1.2.1/24
VLANIF10
10.1.2.2/24
VLANIF20
10.1.3.1/24
Host C
10.1.3.2/24
Eth2/0/2
As shown in Figure 3-14, RouterA is configured with super-VLAN 4, sub-VLAN 2, sub-
VLAN 3, and a common VLAN 10. RouterB is configured with two common VLANs,
namely, VLAN 10 and VLAN 20. Suppose that RouterA is configured with the route to
the network segment 10.1.3.0/24, and RouterB is configured with the route to the network
segment 10.1.1.0/24. Then Host A in sub-VLAN 2 that belongs to the super-VLAN 4 needs
to access Host C in RouterB.
1. After comparing the IP address of Host C 10.1.3.2 with its IP address, Host A finds
that two IP addresses are not in the same network segment 10.1.1.0/24.
2. Host A initiates an ARP broadcast to its gateway to request for the MAC address of
the gateway.
3. After receiving the ARP request, RouterA identifies the correlation between the sub-
VLAN and the super-VLAN, and offers an ARP response to Host A through sub-
VLAN 2. The source MAC address in the ARP response packet is the MAC address
of VLANIF4 for super-VLAN 4.
4. Host A learns the MAC address of the gateway.
5. Host A sends the packet to the gateway, with the destination MAC address as the MAC
address of VLANIF4 for super-VLAN 4, and the destination IP address as 10.1.3.2.
6. After receiving the packet, RouterA performs the Layer 3 forwarding and sends the
packet to RouterB, with the next hop address as 10.1.2.2, the outgoing interface as
VLANIF10.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
3 VLAN Configuration
Issue 01 (2014-11-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
87
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