Hi,You are very right about the Q-in-Q.. I dug a bit deeper into the issue, just because it bothered me actually. I have attached the topology just for clarity.
Basically, as I see it, even though you are transfering STP,CDP and other L2 goodies, doesnt mean you will actually be able to have a working topology. To explain this, you can have the following configuration on SW1:
interface FastEthernet0/1 switchport access vlan 900 switchport trunk encapsulation dot1q switchport mode trunk l2protocol-tunnel cdp l2protocol-tunnel stp l2protocol-tunnel vtpand the same on SW2. I had a vlan 4 defined on both SW3 and SW4, and i was wondering why they both assumed they were root bridge of that particular vlan. Turns out that even though you are tunneling your STP messages through the "provider cloud", in this case SW1 and SW2, you need to have those vlans defined in the "cloud" to work! that means that if you dont have them defined in your cloud, SW3 can send a packet to SW1, as you said, tagged, SW1 then looks at it and imo discards it, because it does not have this vlan defined.
If you instead used a different configuration like this: interface FastEthernet0/1 switchport access vlan 900 switchport trunk encapsulation dot1q switchport mode access l2protocol-tunnel cdp l2protocol-tunnel stp l2protocol-tunnel vtpSW1 would always receive the data on what it thinks is vlan 900, pass it onto SW2, which would send it out un-tagged to SW4. In this case, only things in the native vlan would work, because SW4 would receive un-tagged packets over what it thinks is a trunk, and believe it is native traffic.
So I guess where im heading with all of this is, even though you can pass STP,CDP and other good stuff, unless your provider has the vlans defined, you will only be able to use the native vlan. This is where Q-in-Q comes into play. It preserves the tags + only uses 1 vlan in the cloud for ALL the customer vlans.
I hope im right about this and that it makes sense :) Sincerely, Kim Pedersen Rick Mur wrote:
The Q-in-Q is for tunneling 802.1Q tagged packets throughout a 'service provider' network. If you don't have the need for Q-in-Q but want to do like ether-channeling across a 3rd party network, you need the l2protocol tunnel. Like the Cisco Documentation you linked specified it does some magic with MAC addresses. To me the only use for it, without Q-in-Q, is etherchannel. CDP and STP is nice, but would you ever want a huge STP domain across multiple sites in real life?-- Regards, Rick Mur CCIE2 #21946 (R&S / Service Provider) Sr. Support Engineer – IPexpert, Inc. URL: http://www.IPexpert.com On 5 sep 2009, at 15:36, prakash patel wrote:BasicallyFirst create tunnel..Q in Q Then Layer 2 protocol like CDP, STP etc will be going thru tunnel..that is called layer 2 protocl tunnel :-).this featuer needs tunnel. WHich protocol will be allowed through the tunnel ?. > Date: Sat, 5 Sep 2009 15:25:01 +0200> From: [email protected] <mailto:[email protected]> > To: [email protected] <mailto:[email protected]> > CC: [email protected] <mailto:[email protected]> > Subject: Re: [OSL | CCIE_RS] QinQ Vs. l2protocol-tunnel> > Hi Rick, > > Thanks for taking the time to help out! im pulling out the remaining > hairs on my head! :) > > I found the missing piece by going over the configuration i was going > to send :) > (I even pulled out a 2950 i was using as SW3, and replaced it with a > 3550... just to make sure...) > > But if you dont mind, how is the l2protocol-tunnel different from QinQ > (other than the packets are double tagged). From my now working > topology, all my vlans run STP, CDP just fine... I think im missing the > point somewhere along the path.. > > Thanks again! > > Kim > > Rick Mur wrote:> > Hi Kim, > >> > Please see my attached drawing. I configured about the same topology > > as you did. Trunk between SW3 and SW4 and access ports to SW1 and SW2. > > On those access ports I enabled l2-protocol-tunnel cdp and now SW1 and > > SW2 see each other as CDP neighbor over those interfaces.> > > > Please show me your entire configuration if this doesn't work for you. > > Again see attached drawing for more clarification on my topology :-) > > > > > > -- > > > > Regards, > > > > Rick Mur > > CCIE2 #21946 (R&S / Service Provider) > > Sr. Support Engineer – IPexpert, Inc. > > URL: http://www.IPexpert.com > > > >> > On Sat, Sep 5, 2009 at 1:39 PM, Kim Pedersen <[email protected] <mailto:[email protected]> > > <mailto:[email protected]>> wrote:> > > > Hi all, > > > > I have been reading over > >http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.2_44_se/configuration/guide/swtunnel.html#wp1014851 > > 10 times by now, and I am still unsure of the difference. > > > > I have tried to set up a lab to test some stuff out, it consists of 4 > > switches: > > > > SW3 is connected to SW1 and SW4. > > SW4 is connected to SW3 and SW2 > > and SW1 and SW2 are connected. > > > > I want SW3 to see SW4 through SW1 and SW2. To accomplish this, i have > > set up a vlan (13) on both SW1 and SW2, then an access port on > > each with > > vlan 13 is connected to SW3 and SW4 respectively. On top of this, > > i use > > l2protocol-tunnel on each of these interfaces. I was expecting CDP > > traffic to flow from SW3 to SW1, through the trunk between SW1 and > > SW2, > > and from SW2 to SW4. But this does not happen. > > > > I think generally im confused between the difference between QinQ > > and l2 > > protocol tunneling. Can someone shed some light on this or maybe point > > me in the correct direction through some documentation apart from the > > above Cisco Doc... > > > > Thanks! > > > > Sincerely, > > Kim Pedersen > > > > -- > > > > // Freedom Matters > > // Follow my progress on: http://kpjungle.wordpress.com > > > > _______________________________________________ > > For more information regarding industry leading CCIE Lab training,> > please visit www.ipexpert.com <http://www.ipexpert.com> <http://www.ipexpert.com>> > > > > >> > ------------------------------------------------------------------------> >> > -- > > // Freedom Matters> // Follow my progress on: http://kpjungle.wordpress.com> > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com <http://www.ipexpert.com>------------------------------------------------------------------------Windows Live: Keep your friends up to date with what you do online. Find out more. <http://windowslive.com/Campaign/SocialNetworking?ocid=PID23285::T:WLMTAGL:ON:WL:en-US:SI_SB_online:082009>_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com <http://www.ipexpert.com>
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