From: Bob Sinclair (bobsinclair@frontiernet.net)
Date: Thu Aug 25 2005 - 23:47:45 GMT-3
Stephen,
As shown below, the 3550 associates routed ports with internal vlans (starting
at 1025) but it does not associate loopbacks with them.
CAT3550#sh vlan internal usage
VLAN Usage
---- --------------------
CAT3550#c
Enter configuration commands, one per line. End with CNTL/Z.
CAT3550(config)#int f0/2
CAT3550(config-if)#no switchport
CAT3550(config-if)#end
CAT3550#sh vlan internal usage
VLAN Usage
---- --------------------
1025 FastEthernet0/2
CAT3550#c
Enter configuration commands, one per line. End with CNTL/Z.
CAT3550(config)#int loop 1
CAT3550(config-if)#ip address 1.1.1.1 255.255.255.0
CAT3550(config-if)#end
CAT3550#sh vlan internal usage
VLAN Usage
---- --------------------
1025 FastEthernet0/2
CAT3550#
HTH,
Bob Sinclair
CCIE #10427, CCSI 30427, CISSP
www.netmasterclass.net
----- Original Message -----
From: Stephen Hull
To: ccielab@groupstudy.com
Sent: Thursday, August 25, 2005 10:08 PM
Subject: Loopbacks and VLANs
I have a question about Loopbacks and VLANs and I was hoping someone
could help me with this. I have searched the GS archives and found
nothing and I have read a lot of the Cisco DocCD and still can't find
the answer. My question is this. When you create a loopback interface
on a switch, what VLAN does it get put into? I know you can include the
network address of the loopback into routing protocols, but what VLAN
would it actually be in? I know that it is not necessary to put the
loopback into a VLAN and I am not sure if you actually can do that. I
guess with some manipulation you could. Anyway, I am running a lab
scenario right now where the switch is peering with a router with eBGP
and it is using the loopback on the switch. It just occurred to me
after looking more at the configs that I was not peering with the
"directly" connected interface. If I were using a directly connected
interface, it would be one of the VLAN interfaces where I have added an
I P address.
I was wondering if someone could shed some light on this. I am just
trying to learn more about the operations and logic behind the routers
and switches.
Thanks for any help. It is greatly appreciated.
-Stephen
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