Go CCIE Go!! - A Cisco Certified Internetwork Expert

I think I found my answer reading the DocCD again:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_44_se/configuration/guide/swtunnel.html#wp1043351
“When the Layer 2 PDUs that entered the service-provider inbound edge switch through a Layer 2 protocol-enabled port exit through the trunk port into the service-provider network, the switch overwrites the customer PDU-destination MAC address with a well-known Cisco proprietary multicast address (01-00-0c-cd-cd-d0).”
This pretty much answers my questions. CAT1 sees that cisco proprietary address and knows it was a tunneled packet.
Another good conversation here:
http://www.groupstudy.com/archives/ccielab/200710/msg02522.html
On Wed, Aug 6, 2008 at 11:09 AM, Hobbs wrote:
> Thanks. I admit its hard to ask a question, when your not sure how to ask > it > > I will be labbing it again in a few hours in some online rack time. These > are notes from my last session and I wanted to get a good understanding > before doing it again. fyi, it is actually the beginning of ipexpert’s > version 10, volume 2, section 5 on l2 protocol tunneling. There will be a > couple more switches involved, but this is just the beginning. > > it’s a very interesting lab…just having a hard time grasping the concept. > > > > On Wed, Aug 6, 2008 at 11:02 AM, Jonathan Greenwood II wrote: > >> No I read your questions, and thats my fault. I have to lab it up to >> test. >> >> But my thoughts on question 1: Yes the forwarding behavior would be >> correct since you have the l2protocol-tunnel cdp. I haven’t used it in that >> manner without the switchport mode dot1q-tunnel. >> My thoughts on question 2: Yes Dest Mac will be the same. >> >> My thoughts on question 3: Can you post your output when you do the sh >> cdp nei on CAT2 Fa0/23? I think its not showing BB1 as a neighbor on CAT2 >> Fa0/23 because you are not performing dot1q-tunneling. I don’t think a >> regular trunk overrides the cdp tunneling behavior but more so its not how >> the technology works with that particular configuration. >> >> I have to lab it up myself to play with that scenario you have setup. >> Sorry on my lack up reading earlier but those are my thoughts on your >> question. >> >> R/ >> >> Jonathan >> On Wed, Aug 6, 2008 at 11:47 AM, Hobbs wrote: >> >>> Jonathan, it is a question. I am not looking for a command to make it >>> work. it is working. please read the entire email. If my question doesn’t >>> make sense, I can try and rephrase. >>> >>> >>> On Wed, Aug 6, 2008 at 10:42 AM, Jonathan Greenwood II >> gwood83@gmail.com> wrote: >>> >>>> Just turn off cdp on that particular port on CAT1 connecting to BB1. >>>> “no cdp enable” >>>> >>>> >>>> On Wed, Aug 6, 2008 at 11:37 AM, Hobbs wrote: >>>> >>>>> Thank you for the reply, but I am not having any configuration issues. >>>>> It is only a question. I don’t want CAT1 to see BB1 as a neighbor, I am just >>>>> trying to understand why it doesn’t. >>>>> >>>>> I am not doing dot1q tunneling >>>>> >>>>> >>>>> On Wed, Aug 6, 2008 at 10:32 AM, Jonathan Greenwood II >>>> gwood83@gmail.com> wrote: >>>>> >>>>>> You need to change the switchport mode from access to dot1q-tunnel. >>>>>> >>>>>> On Wed, Aug 6, 2008 at 11:27 AM, Hobbs wrote: >>>>>> >>>>>>> Hello, >>>>>>> >>>>>>> I am trying get my head around a semi-complex protocol tunneling >>>>>>> task, but I >>>>>>> have some questions on the basics. >>>>>>> >>>>>>> Here’s the topology >>>>>>> >>>>>>> “Near end host”: BB1 >>>>>>> “Far end switch”: CAT2 >>>>>>> >>>>>>> [BB1]f0/1—–f0/11[CAT1]f0/23—–dot1q >>>>>>> trunk—–f0/23[CAT2]f0/1—–f0/1[R1] >>>>>>> >>>>>>> To get cdp tunneling to work (and it does work) I enable this on CAT1 >>>>>>> and >>>>>>> CAT2 access ports: >>>>>>> >>>>>>> CAT1: >>>>>>> interface f0/11 >>>>>>> switchport mode access >>>>>>> switchport access vlan 100 >>>>>>> l2protocol-tunneling cdp >>>>>>> no cdp enable >>>>>>> >>>>>>> CAT2: >>>>>>> interface f0/1 >>>>>>> switchport mode access >>>>>>> switchport access vlan 100 >>>>>>> l2protocol-tunneling cdp >>>>>>> no cdp enable >>>>>>> >>>>>>> The trunk between CAT1 and CAT2 carries vlan 100 as well as others. >>>>>>> >>>>>>> This is what I understand so far: >>>>>>> >>>>>>> BB1 sends a multicast CDP packet on it’s port to CAT1. >>>>>>> Since CAT1 has cdp tunneling enabled, it forwards it rather than >>>>>>> processes >>>>>>> it. Is this correct? >>>>>>> CAT1 sends this packet out all trunk links that have vlan 100 allowed >>>>>>> AND >>>>>>> any access ports on VLAN100. Is this correct? >>>>>>> The packet still has the cisco CDP destination MAC. Is this correct? >>>>>>> The packet is dot1q tagged and sent out port fa0/23 and still has >>>>>>> cisco CDP >>>>>>> destination MAC address. Is this correct? >>>>>>> >>>>>>> Question: >>>>>>> >>>>>>> CAT2 doesn’t have tunneling on port fa0/23. >>>>>>> Why doesn’t CAT2 now process this CDP packet and show BB1 has a CDP >>>>>>> neighbor >>>>>>> on fa0/23? >>>>>>> Does trunking override this behavior? >>>>>>> Does CAT2 treat this packet differently because it is a tagged CDP >>>>>>> packet? >>>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>> >>>>>>> Blogs and organic groups at http://www.ccie.net >>>>>>> >>>>>>> >>>>>>> _______________________________________________________________________ >>>>>>> Subscription information may be found at: >>>>>>> http://www.groupstudy.com/list/CCIELab.html
Blogs and organic groups at http://www.ccie.net