Information Technology Reference
In-Depth Information
Step 4
Use the set interface sc0 172.16.84.17 255.255.255.0 172.16.84.255 command on Switch A and the set
interface sc0 172.16.84.18 255.255.255.0 172.16.84.255 command on Switch B to assign IP addresses
from the same subnet to the management ports on both switches. The VLAN for sc0 (the management
VLAN) must also be specified in this command if it is different than the default of VLAN 1.
Switch-A> (enable) set int sc0 172.16.84.17 255.255.255.0 172.16.84.255
Interface sc0 IP address, netmask, and broadcast set.
Switch-A> (enable)
Step 5
Verify that the link between switches A and B is not trunking by entering the show trunk 1/1 command
on Switch A.
Switch-A> (enable) show trunk 1/1
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/1 auto isl not-trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
1/1 1-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
1/1 1
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
1/1 1
Switch-A> (enable)
The term Native vlan in the output indicates the VLAN in which this port will be placed
when it is not in trunking mode. If the port is instead configured for 802.1q trunking,
Native vlan also indicates the VLAN for whose frames will be untagged; all others will be
tagged (conversely, with ISL trunking, every data frame is tagged with the appropriate
VLAN identifier).
Note
The trunking status should read “not-trunking” because the default mode for the Dynamic Trunking
Protocol (DTP) is Auto. DTP is the strategic replacement for Dynamic ISL (DISL) because it
incorporates support for 802.1q trunking negotiation. DTP is available as of version 4.x Catalyst
software and certain hardware modules. The following bullets describe the five different states for which
DTP can be configured.
Auto —The port listens for DTP frames from the neighboring switch. If the neighboring switch
indicates that it would like to be a trunk, or if it is a trunk, then Auto state creates the trunk with the
neighboring switch. Auto does not propagate any intent to become an trunk; it depends solely on the
neighboring switch to make the trunking decision.
Desirable —DTP is spoken to the neighboring switch. This communicates to the neighboring switch
that it is capable of being an ISL trunk and would like the neighboring switch to also be an ISL trunk.
On —DTP is spoken to the neighboring switch. This automatically enables ISL trunking on its port,
regardless of the state of its neighboring switch. It remains an ISL trunk unless it receives an ISL
packet that explicitly disables the ISL trunk.
Nonegotiate —DTP is not spoken to the neighboring switch. This automatically enables ISL
trunking on its port, regardless of the state of its neighboring switch.
Off —ISL is not allowed on this port, regardless of the DTP mode configured on the other switch.
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