From: Guyler, Rik (rguyler@shp-dayton.org)
Date: Mon Mar 13 2006 - 14:07:20 GMT-3
As I mentioned, I did not have the exact config options that you posted.
You didn't mention a particular model or OS version so I labbed it up on
what I had.
Rik
-----Original Message-----
From: Geert Nijs [mailto:geert.nijs@simac.be]
Sent: Monday, March 13, 2006 11:42 AM
To: Guyler, Rik; ccielab@groupstudy.com
Subject: RE: Trunk Modes theory
Be ware. Your first switch does not have the nonegotiate option. This is
critical.
Currently switch SW1 is running in default mode which is "desirable". Of
course "desirable" - "desirable"
works (at least when encapsulations match).
Nonegotiate will drop DTP packets and the "desirable" side will fail to form
a trunk. NO?
Geert
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Guyler, Rik
Sent: maandag 13 maart 2006 17:17
To: 'ccielab@groupstudy.com'
Subject: RE: Trunk Modes theory
Yes, a trunk gets formed. Here is the output from my switches (3550's) that
I just labbed up for you. The config is not identical to yours but looks
like it provides the same functionality:
SW1#sh run int f0/24
Building configuration...
Current configuration : 93 bytes
!
interface FastEthernet0/24
switchport trunk encapsulation isl
switchport mode trunk
end
SW1#sh int trunk
Port Mode Encapsulation Status Native vlan
Fa0/24 on isl trunking 1
Port Vlans allowed on trunk
Fa0/24 1-4094
Port Vlans allowed and active in management domain
Fa0/24 1,888
Port Vlans in spanning tree forwarding state and not pruned
Fa0/24 1,888
SW1#sh run int vlan 888
Building configuration...
Current configuration : 62 bytes
!
interface Vlan888
ip address 10.111.111.111 255.0.0.0
end
SW1#
SW2#sh run int f0/24
Building configuration...
Current configuration : 97 bytes
!
interface FastEthernet0/24
switchport mode dynamic desirable
end
SW2#sh int trunk
Port Mode Encapsulation Status Native vlan
Fa0/24 desirable n-isl trunking 1
Port Vlans allowed on trunk
Fa0/24 1-4094
Port Vlans allowed and active in management domain
Fa0/24 1,888
Port Vlans in spanning tree forwarding state and not pruned
Fa0/24 1,888
SW2#sh run int vlan 888
Building configuration...
Current configuration : 62 bytes
!
interface Vlan888
ip address 10.222.222.222 255.0.0.0
end
SW2#ping 10.111.111.111
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.111.111.111, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms SW2#sh
cdp nei Capability Codes: R - Router, T - Trans Bridge, B - Source Route
Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID Local Intrfce Holdtme Capability Platform Port
ID
SW1 Fas 0/24 121 S I WS-C3550-2Fas
0/24
R11 Fas 0/11 139 R S I Cisco 2801Fas
0/1
R2 Fas 0/2 135 R 2500 Eth
0
R3 Fas 0/3 144 R 2500 Eth
0
R1 Fas 0/1 158 R 2500 Eth
0
SW2#
Rik
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Geert Nijs
Sent: Monday, March 13, 2006 10:21 AM
To: ccielab@groupstudy.com
Subject: Trunk Modes theory
All,
I am studying for my recertification and although i do understand the
different trunking modes, there has been a large discussion between me and a
colleague for the following specific situation:
First Situation
SW1 - Fa0/1
switchport mode trunk
switchport trunk mode isl
switchport trunk nonegotiate
SW2 - Fa0/1
swichport mode desirable
Is an ISL trunk being formed or NOT ?
Trick: nonegotiate makes the port NOT send any DTP packets.
I always thought that "desirable" NEEDED DTP packets from the other side to
form a trunk (so: ON, AUTO or DESIRABLE) So i would say: NO, their is no
trunk.
Several books and docs seem to suggest that in this case, a trunk will be
formed. I am unable to test right now.
So what will happen ?
regards,
Geert Nijs
Service Engineer
CCIE #13729 <http://www.cisco.com/en/US/learning/le3/ccie/index.html>
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