Filter
Top Products
1-4
Introduction
1.3.3 802.1Q Trunk Ports
An 802.1Q trunk port passes all packets with the tag in place. It will not strip the
tag. The port must be a hybrid port. There is no explicit command to create
802.1Q trunks ports. The following are two ways of implementing trunk ports:
• Preserving Priority. The default port VLAN ID (PVID) must be identical at
both ends of the trunk link. The PVID used must be a value not used anywhere
else in the network to pass traffic. Because this VLAN ID is unique, it will not
be stripped from the packet on egress and therefore will pass the priority bits
intact.
• Non-Preserving Priority. The default port VLAN ID (PVID) must be identical
at both ends of the trunk link. The VLAN ID will be stripped on egress and re-
inserted on ingress. However, the priority bits will be lost.
1.3.3.1 Preserving Priority
The 802.1Q trunk passes all packets with the tag in place. It will not strip the tag.
All packets traversing the link will contain a tag. The administrator should set a
policy that certain VLAN IDs must be reserved and must not be used for traffic.
For example, when reserving VLAN IDs 0xff0 through 0xffe, one of these can be
used as the PVID for both ends of trunk links. By doing this, the priority bits can
be passed intact. Both ends of the link should be defined as Hybrid so that they
only strip tags if they match the PVID. Because the tag in the packet traversing
the trunk will never match the PVID, it will not be stripped. Also, because the
packet is always received with a tag, the PVID is never inserted.
Preserving priority works best when the end device inserts the tag and supports
priority (priority is not used by the ELS10-27TX, but is passed within the
packet). Therefore, the trunk will not strip a tag or insert a tag, thus the priority
fields are passed intact.
NOTE
All VLAN ports by default are hybrid ports.