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CCNA Switch Subintf question

Posted on 2004-09-16
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Last Modified: 2010-04-10
Hey, i got the test tommorow and a quick question:

On a switch (1900 or 2950), when you want to configure Inter-VLAN Routing, what are the proper configuration steps?

Is is
switch#config t
switch(config)#int f0/0.1
switch(config-subif)#encapsulation isl (or dot1q for 2950) "vlan#"

or did i miss something?  Thanks!
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Question by:smashmouthftball
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lrmoore earned 300 total points
ID: 12083861
You cannot configure inter-vlan routing on either a 1900 or a 2950. You need a layer 3 switch to do that.
However, you can use a "router-on-a-stick".
Switchport setup for trunking
ROUTER interface:

ROUTER#config t
ROUTER(config)#int f0/0.1
ROUTER(config-subif)#encapsulation isl (or dot1q for 2950) "vlan#"
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by:smashmouthftball
ID: 12084922
Ahh now that makes sense...telling the router to move packets from switch to switch...do you have to put in the encapsulation isl (or dot1q for 2950) "vlan#" command for each vlan you want to route through the router, or will just one do?
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Expert Comment

by:lrmoore
ID: 12084993
You have to have a separate router sub-interface for each VLAN, so yes, you need to specify the encap and the vlan#
i.e.

interface fa0/0
  ip address x.x.x.1 255.255.255.0

interface f0/0.2
  ip address x.x.y.1 255.255.255.0
 encap dot1q 2

interface f0/0.3
 ip address x.x.z.1 255.255.255.0
 encap dot1q 3

<etc>
Notice that VLAN 1 does not require a sub-if. The major interface F0/0 in this case, will automatically recognize VLAN1 traffic without specifying encapsulation or vlan#

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