local/global dlci

jamesleecoleman

I've been reading the ICND2 book by Odom and I'm really confused.
I understand that a DLCI is different for every VC. I just don't understand
whats the difference between local and global dlci. I've tried to look it up
online but thats not helping me. Can someone help me out here??

Netwurk

A local DLCI is only locally significant, a global one is globally significant. There's much more to it of course. Read on...

Cisco Frame Relay Configurations > Local Significance Approach to DLCI Assignment


Luckily, the sample chapter I linked (from one of my favorite books) covers a lot regarding your question.

jamesleecoleman

Yea, I still don't understand. Sorry.

thehourman

jamesleecoleman wrote: »

Yea, I still don't understand. Sorry.

This is how I see the difference.
In global dlci, the main site has only one dlci.
In local dlci, the main site has its own dlci value for each dte on the other end.

For example: (check the pic attachment)
The global dlci is using only one dlci value, which is 100, so all the routers that have pvc's to R1 are using dlci 100 to reach R1.

And the second pic is the local dlci. R1 has a dedicated dlci value for each pvc.

wbosher

I think Jeremy summed up DLCIs the best in CBT Nuggets. He said to think of DLCIs like the gates at an airport terminal. When you board the plane (the FR cloud) you leave at gate 100 (DLCI 100), when you land at your destination, you exit the plane (the FR cloud) on gate 200 (DLCI 200). You not going to DLCI 200.

When configuring DLCIs on a router you always map the remote IP address to the local DLCI, the one you are using to enter the FR cloud, not the one you exit out of at the other end.

If you can, I would suggest watching that video. It makes it really clear and easy to understand.

jojopramos

wbosher is correct. The way I see it, you need your DLCI (local) to map the frame relay if not using inverse ARP so the best way to understand that is your local DLCI assigned by the ISP/Telco is the base DLCI going to the connection of ISP and the other/branch site. So, the important thing to understand here is that for example that you are configuring a multipoint frame-relay, you need to know the local DLCI to map with the ip address of the site to make adjacent connection.

example: frame-relay map ip 192.168.1.2 502 broadcast (502 is the dlci here going to 192.168.1.2 connection)

Zartanasaurus

wbosher wrote: »

I think Jeremy summed up DLCIs the best in CBT Nuggets. He said to think of DLCIs like the gates at an airport terminal. When you board the plane (the FR cloud) you leave at gate 100 (DLCI 100), when you land at your destination, you exit the plane (the FR cloud) on gate 200 (DLCI 200). You not going to DLCI 200.

When configuring DLCIs on a router you always map the remote IP address to the local DLCI, the one you are using to enter the FR cloud, not the one you exit out of at the other end.

If you can, I would suggest watching that video. It makes it really clear and easy to understand.

Agree 100%. I was confused after reading the Odom book and after watching the CBTNugget video it was as clear as day.

altjx

Thank you everyone for your feedback in this thread.

I apologize for reviving an old thread, but I'd like to question some of the answers in here. I understand the concepts behind global and local DLCI, but according to ICND2, if there's only two routers, you can't really determine based on looking at a diagram. They say the best way is to look at the configuration and the show commands.

My question here is if you just have two routers, how do you determine if they're using global or local DLCI based on show/configuration commands? Both routers are going to have a local DLCI of the opposite router's local DLCI value, correct? How do you determine the difference from two routers?

Also, is it true that to tell if a frame relay network is using local or global DLCI, you'd have to look at multiple router's configuration to determine if they're all pointing to a main site (using the same DLCI)? Is there a way to determine local/global DLCI based on having access to only one router?

pham0329

The Local/Global DLCI is just a term that we use to make it easier when documenting...it's not a type of DLCI. As such, there isn't a command that would show you whether a DLCI was "Global" or "Local"....it's all the same to the router.

Just think of a global DLCI as an ip address. If R1 has to contact R2, we would configure R1 to use R2's global DLCI.

altjx

pham0329 wrote: »

The Local/Global DLCI is just a term that we use to make it easier when documenting...it's not a type of DLCI. As such, there isn't a command that would show you whether a DLCI was "Global" or "Local"....it's all the same to the router.

Just think of a global DLCI as an ip address. If R1 has to contact R2, we would configure R1 to use R2's global DLCI.

Correct, but in the case where you only have two routers, how do you determine if they're using global or local DLCI addressing?

pham0329

Well, I guess my response would be, does it matter? Does it change the way the packet travels in any way?

In any case, it depends on how the network is documented. For example, if you have a network diagram with "100" above R1, and "200" above R2, chances are, you're looking at global DLCIs

I think you guys are reading into this too much. Local DLCI just means its locally signifcant, meaning that other routers could have the same dlci number assigned to an interface. So, if R1's "global" dlci is 100, you would configure R2 to use dlci 100 to reach R1. Does that mean "100" is a global or local dlci? 100 is R1's global DLCI, but it's also "local" in that if R3 needs to reach R1, it would also use 100.

altjx

pham0329 wrote: »

Well, I guess my response would be, does it matter? Does it change the way the packet travels in any way?

In any case, it depends on how the network is documented. For example, if you have a network diagram with "100" above R1, and "200" above R2, chances are, you're looking at global DLCIs

Well, I was only trying to find out for exam purposes. I'm not sure what or how deep the exam is going to go into DLCI, but the text states that the exam is going to ask questions regarding global/local addressing, and in a question it may ask you to find out whether they're using local or global addressing (based upon only two routers and not enough hints on diagram) -- it says you may have to find out using show commands.