At 06:33 PM 6/24/2003 +0000, Priscilla Oppenheimer wrote: >Aaron Ajello wrote: > > > > This is probably a very simple concept question, but I've asked > > a couple people and haven't gotten a solid answer. > > > > If I've got two frame relay spoke sites connected point to > > point with a hub site and a server in one spoke site copies a > > file to a server in the other spoke site, does all the traffic > > pass through the hub site, or is it switched within the frame > > cloud? > >All the traffic passes through the hub site. > > > > > I guess what I'm wondering is does a frame cloud act somewhat > > like a lan, where initially packets will go through the default > > gateway and be routed and then the following packets will be > > switched? > >A frame cloud does act like a LAN but a LAN without a router (and no >broadcasting, but that's another story). You mixed metaphors by sticking in >the router, which is a layer up. The only reason a LAN switch can route and >then switch is because it's really a router (dare I say L3 switch!? :-) Or >it is in communication with a router, running Cisco's Multilayer Switching >Protcol (MLSP), and has an understanding of L3 addressing. > >A Frame Relay switch is just a L2 switch. It really does behave quite a bit >like a classic LAN L2 switch. It has a switching table that has a set of >entries that say, "if packet comes in on this DLCI, it goes out on that >DLCI." This is similar to a L2 bridging/switching cam table, although there >are differences.
The main differences being that a.) the FR switch typically doesn't learn the DLCI numbers dynamically, rather the service provider needs to configure it hop-by-hop, and b.) the DLCI is not a globally unique identifier, like the MAC address in the case of an Ethernet switch, rather has only local significance and it might change along the path (aka PVC) from switch to switch. Thanks, Zsombor >The Frame Relay switch understands the virtual circuits that have been >provisioned to the customer. > >With a hub and spoke topology, the spokes don't have a virtual circuit to >each other. They just have a virtual circuit to the hub. > >So imagine a hub and spoke topology with Chicago being the Hub. Make Los >Angeles and Miami the spokes. > >Chicago has two virtual circuits: > >DLCI 100 goes to Los Angeles >DLCI 200 goes to Miami > >Los Angeles has just one virtual circuit: >DLCI 777 goes to Chicago > >Miami has just one virtual circuit >DLCI 888 goes to Chicago > > >A switch in Chicago has two entries in its switching table: > >incoming = 100, outgoing = 777 >incoming = 200, outoing = 888 > > >A switch in Los Angeles has the following entry in its switching table > >incoming = 777, outgoing = 100 > > >A switch in Miam has the following entry in its switching table > >incoming = 888, outgoing = 200 > > >If you can get your hands on enough routers, set up one of them to be a >Frame Relay switch in a hub-and-spoke topology. Just a switch, no routing. >It's truly an eye opener to manually configure its switching table (and it >is generally done manually, unlike a LAN switch.) > >Actually, from what I understand, there can be intermediate DLCIs in the >cloud too, but that's a high-level view. Someone can correct me if I'm wrong >about it. I'm a bit tired after the NetBIOS biopsy or was it a lobotomy. :-) > > > >Priscilla > > > > > thanks. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=71289&t=71263 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
