3Com CoreBuilder 3500, Implementation Manual

Page: 202 / 592

202 C
HAPTER
9: V
IRTUAL
LAN
S
Rules for
Network-based
(Layer 3) VLANs
Whenever an IP VLAN is defined with Layer 3 information, another VLAN,
called the
All IP Subnets VLAN, is defined over the same ports.
Information about this VLAN is not available to the network
administrator. Also, this VLAN has no VID associated with it and has no
IEEE 802.1Q tagging on any of the ports. Incoming IP frames are assigned
to this VLAN if they cannot be assigned to any of the network-based IP
VLANs.
You can either configure network-based IP VLANs (IP VLANs with unique
Layer 3 IP addresses) or you can define a single protocol-based VLAN with
the protocol type IP and then define multiple IP routing interfaces for that
VLAN.
The following IP protocols are applicable to network-based VLANs:
■
IP (hexadecimal 0800 or 0x0800)
■
ARP (0x0806)
■
RARP (0x8035)
The frames associated with these protocols have different ingress rules for
assignment to the appropriate network-based VLAN:
■
IP frames — These frames are assigned to the network-based IP
VLAN if the IP source address is consistent with the VLAN subnetwork
and the IP destination address is one of the following:
■
0.0.0.0
■
255.255.255.255
■
A Class D (multicast) address
Otherwise, assign the frame to the network-based IP VLAN if the IP
destination address is consistent with the VLAN subnetwork.
Otherwise, assign the frame to the
All IP Subnets VLAN.
■
ARP frames — These frames are assigned to the network-based IP
VLAN if the IP destination address is consistent with the VLAN
subnetwork and the IP source address is 0.0.0.0. Otherwise, assign the
frame to the network-based IP VLAN if the IP source address is
consistent with the VLAN subnetwork. Otherwise, assign the frame to
the
All IP Subnets
VLAN.
■
RARP frames — These frames are assigned to the All IP Subnets
(multicast) VLAN.