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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 14 Configuring VLA Ns Configurin g VLAN Trunks
Beginning i n privileged EX EC mo de, foll ow these s teps to c onfigure th e nat ive VLA N on a n 8 02.1Q
trunk:
To return to the default native VLAN, VLAN 1, use the no switchport trunk native vlan in te r fa ce
configurati on comm a nd.
If a packet has a VLAN ID that is the same as the outgoing port native VLAN ID, the packet is sent
untagg ed; otherwi se, the swi tch sends the pa cket with a tag.

Load Sharing Using STP

Load sha r ing d ivides the ban dw idth supp lied by par a llel t ru nks co nne ct ing s witc he s. To avoi d loop s,
STP norma ll y bl ock s al l but one para ll el link b etw een swit ches. Usi ng load sha ring , you divide the
traffic between the links according to which VLAN the traffic belongs.
You configure lo ad sharing on trunk ports by using STP port priorities or STP path costs. For lo ad
sharing using STP port priorities, both load-sharing links must be connected to the same switch. For load
sharing using STP path costs, each load-sharing link can be connected to the same switch or to two
different switches. For more information about STP, see Chapter 11, “Configuring STP.”

Load Sharing Using STP Port Priorities

When two ports on the same switch form a loop, the STP port p riority setting determines which port is
enabled and which port is in a blocking state. You can set the priorities on a parallel trunk port so that
the port carries all the traffic for a given VLAN. The trunk port with the higher priority (lower values)
for a VLAN is forwarding traffic for that VLAN. The trunk port with the lower priority (higher values)
for the sam e VLAN remains in a blocking state for th at VLAN . One trun k port send s or receives all
traffic for the VLAN.
Figure 14-3 shows two trunks conne cting s upported s witches. In t his example, the switches ar e
configured a s f ol lows:
•VLANs 8 through 10 ar e assigne d a port prio rity of 10 on Trunk 1.
•VLANs 3 t hroug h 6 r eta in the default p ort prior ity o f 128 on Trunk 1.
•VLANs 3 t hroug h 6 a re a ssign ed a po rt pri or ity o f 1 0 on Tr unk 2.
•VLANs 8 thr ough 10 re tain the default port priori ty of 128 on Trunk 2.
Command Purpose
Step 1 configure terminal Enter glob al co nfigur atio n mo de .
Step 2 interface interface-id Enter interface configuration mode, and define the interface that is
configured a s the 802 .1Q trunk .
Step 3 switchport trunk native vlan vlan-id Con figure the VL AN tha t is sendi ng and re ceiving untagg ed traffic
on the trunk por t.
For vlan-id, the range is 1 to 4094 whe n the EI is in stalle d, and 1 to
1005 when the SI is installed. Do not enter leading zeros.
Step 4 end Return to privileged EXEC mode.
Step 5 show interfaces interface-id switchport Ve rify your entries in the Trunking Native Mode VLAN fie l d .
Step 6 copy running-config startup-config (Optional) Save yo ur entries in the configuration file.