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correction: *CAT2 *sees that cisco proprietary address and knows it was a tunneled packet.
On Wed, Aug 6, 2008 at 11:31 AM, Hobbs wrote:
> 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
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