Re: Trunk Modes theory

From: James Ventre (messageboard@ventrefamily.com)
Date: Mon Mar 13 2006 - 15:33:49 GMT-3


Try: "switchport nonegotiate" ..... not "switchport mode nonegotiate".

James

Guyler, Rik wrote:
> SW1#sh ver
> Cisco Internetwork Operating System Software
> IOS (tm) C3550 Software (C3550-I5Q3L2-M), Version 12.1(22)EA5, RELEASE
> SOFTWARE (fc1)
>
> SW1(config-if)#sw mod ?
> access Set trunking mode to ACCESS unconditionally
> dot1q-tunnel Set trunking mode to DOT1Q TUNNEL unconditionally
> dynamic Set trunking mode to dynamically negotiate access or trunk
> mode
> trunk Set trunking mode to TRUNK unconditionally
>
>
> I don't have the "nonegotiate" option but by the description of setting it
> to trunk mode, it appears that no negotiation is taking place since it will
> trunk unconditionally. Does this mean no negotiation or is DTP still being
> output from the switch? I interpret this to mean that the trunk is turned
> on with the configured encapsulation and no DTP is being sent over the link
> but I may be wrong. I didn't hook up a sniffer to test it so if anybody can
> confirm this one way or the other.
>
> Rik
>
>
> ________________________________
>
> From: Mark Lasarko [mailto:mlasarko@co.ba.md.us]
> Sent: Monday, March 13, 2006 11:26 AM
> To: ccielab@groupstudy.com; rguyler@shp-dayton.org
> Subject: RE: Trunk Modes theory
>
>
> Greetings Rik,
> So what happens when you add the "nonegotiate" line to sw1?
> I'd be interested to hear - also what version are you running?
> Thanx,
> ~M
>
>
>
>>>> "Guyler, Rik" <rguyler@shp-dayton.org> 03/13/06 11:16 AM >>>
>
> 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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