| Author |
A tricky question!!! Try it out!!
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| perfectionist 2004-04-10, 11:36 pm |
| Hie!
I have come accross this question while I was doing and exercise. I think that the answer should be "B" but the answer given is "A". What do you guys think?
Company "A" has its head office in Berlin and a branch office in
Bonn. You are troubleshooting the WAN link between head office and the branch office.
You replace a Cisco router that was providing Frame Relay connectivity at the Bonn site with a frame
relay router from a different vendor. However, connectivity broke down between the two offices.
What is the most likely cause of the problem?
A. Mismatched LMI types.
B. Incompatible encapsulation types.
C. Mismatching IP addresses.
D. Incorrect DLCI. | |
| smrkdown 2004-04-11, 1:00 am |
| The correct answer is B.
Mismatched LMI type does not have any direct bearing on connectivity between dte and dte because LMI is used between the router and its local frame-relay switch, not between the two distant routers. This means that as long as LMI types match between each router and its local frame-relay switch, the end DTEs do not have to use the same LMI type as each other. Also, lmi-type has been autosensing since IOS release 11.2.
Mismatched encapsulation type is most probable because the default for Cisco devices is proprietary Cisco frame relay encapsulation and most other vendors use the non-proprietary IETF. | |
| perfectionist 2004-04-11, 3:16 am |
| Thanks For your replay!! I certainly do have the same opinion as you!!!
But any disagreement form others?? I would really like to hear a second thought from the others!!!
Thanks!!! | |
| Yankee 2004-04-11, 7:44 am |
| A mismatch LMI type will bring a circuit down between the router and the frame switch.If the frame switch is configured for LMI type LMI (which Cisco calls Cisco and carriers call LMI) and the new router from a different vendor doesn't support the LMI type the circuit will not come up.
Yankee | |
| smrkdown 2004-04-11, 10:45 am |
| Of course you have to have the correct LMI type but not between the two routers. I think this question is a review question in the Sybex CCNA Study Guide and then answer is encapsulation type. | |
| dmaftei 2004-04-11, 12:19 pm |
| quote:
Originally posted by smrkdown
Of course you have to have the correct LMI type but not between the two routers.
I think "mismatched LMI types" in answer A refers to the LMI types on router-Bonn and its FR switch, not on router-Bonn and router-Berlin. | |
| smrkdown 2004-04-11, 1:22 pm |
| If that's what it means, then that makes sense. | |
| Holiday72 2004-04-13, 10:00 am |
| The answer would be encapusulation, the question specifies that the replaced bonn router is non-cisco, since Cisco is the default frame-relay encapusulation type that would be the first and most obvious. | |
| popdevil 2004-04-13, 1:02 pm |
| non-cisco - is the key word in the question. If you are using 2 cisco routers then the encap should be HDLC. You would most likely change the encap to PPP. | |
| Holiday72 2004-04-13, 3:17 pm |
| Tell me you're not serious please....
You don't use either PPP or HDLC encapsulation on a frame relay interface. My point was the default frame relay encapsulation is "Propietery Cisco" you would have to change the encapsulation to IETF for a non-cisco router
Router#(config-int)encapsulation frame-relay IETF | |
| smrkdown 2004-04-13, 4:55 pm |
| Holiday72 is right.
The default encapsulation for frame-relay connections is Cisco because if you only type "encapsulation frame-relay" then the proprietary Cisco frame-relay encapsulation is assumed and if you want to use IETF (the only alternative) then you must type "encapsulation frame-relay ietf"
PPP and HDLC are not for frame relay connections. | |
| popdevil 2004-04-13, 6:13 pm |
| yes I was wrong.
Double checked and found the below item:
"Configure the Encapsulation on a Logical Interface
Generally, you configure an interface's encapsulation at the [edit interfaces interface-name] hierarchy level. However, for Frame Relay encapsulation, you can also configure the encapsulation type that is used inside the Frame Relay packet itself. To do this, include the encapsulation statement at the [edit interfaces interface-name unit logical-unit-number] hierarchy level, specifying the frame-relay-ccc or frame-relay-tcc option:" | |
| Yankee 2004-04-14, 5:01 am |
| I have never mismatched encapsulation types but I believe both A and B will down your site. In the real world, LMI mismatch is a more common mistake. Cisco LMI is also proprietary, but widely supported because it gives more info in a debug than the others.
Yankee | |
| Holiday72 2004-04-14, 10:35 am |
| Agreed, both A and B could be the problem. Typically the first thing you should check on a new frame relay install that isn't working is the LMI. However, most frame relay switches have a autodiscovery feature which will lock into whatever LMI type is configured at the customer premise. Just for a tip.. once these switches have locked in it doesn't flip back to auto when it goes down, it maintains it's config. With that said LMI could be an answer, but with a non-cisco router being installed, I would first check the encapsulation type on the subinterface to make sure that the cisco side had the correct encapsulation to communicate with the non-cisco.
Good discussion guys and gals! |
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