Jaycee's Networking

January 8, 2009


Filed under: IOS, VLAN, VTP — Tags: , , , — Jaycee @ 2:42 am

1.Frames cannot leave the VLANs from which they originate.

2. “Router on a stick” runs a single trunk from the switch to the router.
=> All the VLANs will then pass over a single link.
==> The router is passing traffic b/w VLANs, so each frame will be seen twice on the same link.
===> Once to get to the router, and once to get back to the destination VLAN.

3. With a layer-3 switch, every pot can be dedicated to devices or trunks to other switches.

4. Configuring VLANs:

(1) Some IOS models, such as the 2950 and 3550, have a configurable VLAN database with its own configuration mode and commands.
=> The configuration for this database is completely separate fro the configuration for the rest of the switch.
==> A write erase followed by a reload will not clear the VLAN database on these switches.

(2) Configuring throught the VLAN database is a throwback to older models that offered no other way to manage VLANS.
=> All newer switches offer the option of configuring the VLANs throught the normal IOS CLI.
==> Switches like 6500, when running in native IOS mode, only support IOS commands for switch configuration.

(3) Cisco recommends VTP be configured as a 1st step when configuring VLANs.
=> trunks will not negotiate w/o a VTP domain
==> VTP domain is not required to make VLANs function on a single switch

5. CatOS

(1)  CatosSwitch# (enable) set vlan 10 name Lab-VLAN

(2) CatosSwitch# (enable) set vlan 10 6/1,6/3-4

(3) CatosSwitch# (enable) sho vlan


6. IOS Using VLAN Database

(1) If you have an IOS switch with active VLANs, but no reference in the running configuration, it’s possible:

a. they were configured in the VLAN database
b. they were learned via VTP

(2) 2950-IOS# vlan database

(3) 2950-IOS(vlan)# vlan 10 name Lab-VLAN

(4) 2950-IOS(vlan)# show

a. 2950-IOS(vlan)# show current
=> display the current database
b. 2950-IOS(vlan)# show changes

=> the differences b/w the current and proposed database

7. IOS Using Global Commands

(1) 2950-IOS# conf t
2950-IOS(config)# vlan 10
2950-IOS(config-vlan)# name Lab-VLAN

(2) 2950-IOS# sho vlan

(3) 2950-IOS(config)# int f0/1
2950-IOS(config-if)# switchport access vlan 10

(4) 2950-IOS(config)# interface range f0/1-2
2950-IOS(config-if-range)# switchport access vlan 10



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