STP is really not an issue in the kind of application where gigastack makes sense. For example, take an office of 400 users plus servers and printers, occupying a contiguous space. Basic file and print sharing plus an internet connection. Rather than buy a honking 65xx, you throw in a few 3550-48's and gigastack them. The electronics work in conjunction with the switch OS to create a half duplex bus between the switches. ( The interesting thing is that electronics are apparently smart enough to determine if there are only two devices stacked, in which case the bus is full duplex. )
That's the question about gigastack - whether the entire stack is treated as one switch, the way it is for management purposes, or if standard STP applies. We had a thread on this a few weeks ago, but none of us could find an answer in the Cisco documentation. that's why I asked Steven ( who asked Cisco ) what Cisco had to say about spanning tree over a gigastack setup. I'm willing to bet that in a gigastack situation, that STP is disabled ( where it would be enabled if you stacked the switches using the 10/100 ports, or using regular gbics and daisy chaining the gig ports. ) But I can't find documentation that clarifies. This does give me some food for thought. I'm working with a very large university on a switch design. I am pretty sure that they have several instances where their diameter is greater than seven ( building to building to building to core ). However, being the sophisticates they are, I am certain they are running spanning tree per vlan, and in that case the tree would go back only to the core, and so would have a diameter no greater than 4 in any place I can see from their setup. this seems to be another one of the great discussions that make this group valuable. ""Priscilla Oppenheimer"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > At 03:51 PM 5/19/02, Chuck wrote: > >were the people you asked able to address the max STP diameter of 7 issue > >then? > > Maybe they blew off the max STP diameter of 7 issue. ;-) It is just a > recommendation. Even IEEE 802.1D just uses that word (recommendation). > There's nothing in the protocol that would stop you from having a larger > network, is there? The Max Age timer defaults to 20 seconds, so that > doesn't limit you to 7 hops. > > Also, with gigaswitch, do all those 9 switches remain in the spanning tree? > I don't know anything about gigaswitch, as you can probably tell, but I > would think the 7 limit would only apply to the logical topology, if it > applies at all. > > Priscilla > > > > >""Steven A. Ridder"" wrote in message > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > I asked Cisco, and STP treats the stack as separate switches. > > > > > > > > > ""Chuck"" wrote in message > > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > in your travels have you ever run into the gigastack, and its relation > >to > > > > STP? > > > > > > > > the question came up a short time ago. The Cisco gigastack > documentation > > > > does not cover STP - only how gigastack works. > > > > > > > > essentially, using daisy chained gigastack connections, one can connect > >up > > > > to 9 switches. If I understand correctly, the Cisco electronics and > >switch > > > > OS consider this stack a single entity for management purposes - i.e. > >can > > > be > > > > managed from a single IP address. However, Cisco does not say one way > or > > > > another if the electronics and the switch OS treat this stack as a > >single > > > > device for STP purposes. > > > > > > > > I'm guessing, based on this and other discussions that it would have to > >be > > > a > > > > single device for STP purposes. It just would be nice if Cisco would > > > provide > > > > the specific information. > > > > > > > > That brings up the corollary question - if you have on two switches > > > > gigastacked, then how does STP come into play. In a configuration such > >as > > > > this, again if I understand the documentation correctly, the > electronics > > > and > > > > the switch OS behave differently. > > > > > > > > > > > > > > > > > > > > ""Leigh Anne Chisholm"" wrote in message > > > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > Actually, the 5-4-3 rule has everything to do with detecting > >collisions. > > > > > It's > > > > > a limiting factor of distance so that a collision will be detected > > > within > > > > the > > > > > first 64 bytes of a frame's transmission (also known as Ethernet's > > > minimum > > > > > frame size). It's preferable to detect a collision before the frame > > > > leaves > > > > > the buffer of the transmitting interface - so that retransmission can > >be > > > > > accomplished at the data link layer rather than left to upper layers. > > > > > > > > > > Several months ago, Priscilla and I debated the 7 switch rule. If > you > > > > wanted > > > > > to search the archives for the entire thread, it was titled "What's > >the > > > > > diameter of your switched network? [7:17489]" and was discussed at > the > > > end > > > > of > > > > > August, 2001. Here's an excerpt from one of my posts regarding the 7 > > > hop > > > > > limit: > > > > > > > > > > From other statements I've read (Cisco published material) and from > >the > > > > > original excerpt I published, I'd imagine that the placement of the > >root > > > > does > > > > > matter. > > > > > > > > > > "Part of this restriction is coming from the age field BPDU carry: > > > > > when a BPDU is propagated from the root bridge towards the leaves of > >the > > > > > tree, the age field is incremented each time it goes though a bridge. > > > > > Eventually, when the age field of a BPDU goes beyond max age, it is > > > > > discarded. Typically, this will occur if the root is too far away > from > > > > some > > > > > bridges of the network. This issue will impact convergence of the > > > spanning > > > > > tree." > > > > > > > > > > I'd think that if a bridge were to be the third bridge away from the > > > root, > > > > > and > > > > > another switch was the third bridge on the far side of the root, I > > > > wouldn't > > > > > expect to see any problems with MaxAge because I can't see the root > > > being > > > > too > > > > > far from some of the bridges in the network. Now if a bridge were to > >be > > > > the > > > > > seventh, I could see how that would impose a greater delay and > >possibly > > > > > negatively impact the MaxAge parameter. Now my question would be... > > > does > > > > > this > > > > > really apply in today's networks or is this more of a limitation of > > > > > yesteryear's "software-based bridges"? > > > > > > > > > > And essentially, that's the conclusion Priscilla and I came to - that > > > the > > > > 7 > > > > > hop radius doesn't really seem to apply to today's switched > > > > environments... > > > > > You might want to check with her again though - Priscilla just > >authored > > > a > > > > new > > > > > book on troubleshooting campus networks and may updated her thinking. > > > > > > > > > > > > > > > -- Leigh Anne Chisholm (CCNP, CCDP) -----Original Message----- > > > > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf > >Of > > > > > > Steven A. Ridder > > > > > > Sent: Saturday, May 18, 2002 5:16 AM > > > > > > To: [EMAIL PROTECTED] > > > > > > Subject: Re: STP and 7 hops [7:44408] > > > > > > > > > > > > > > > > > > I believe the 5-4-3 rule is for repeaters, not switches. > > > > > > > > > > > > > > > > > > ""Brian Hill"" wrote in message > > > > > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > > > Steven, > > > > > > > > > > > > > > The 7 hop limit is from the root bridge, as STP calculates the > >tree > > > > from > > > > > > the > > > > > > > root. Historically, I am not sure why it's 7, but Ethernet has a > > > base > > > > hop > > > > > > > "limit" of 4 switches (5-4-3 rule), so it doesn't really matter > so > > > > much. > > > > > > The > > > > > > > reason for the 4 hop limit in Ethernet is simple: For 10 Mb or > >full > > > > > duplex > > > > > > > 100 Mb connections, the limit is mostly to reduce noise from the > > > > > > > amplification of the signal as it passes through the > >switches/hubs, > > > > where > > > > > > as > > > > > > > in 100Mb half-duplex connections, it is mostly to keep the > > > propogation > > > > > > delay > > > > > > > within specs. > > > > > > > > > > > > > > Hope this helps, > > > > > > > > > > > > > > Brian Hill > > > > > > > CCNP, CCDP, MCSE 2000 (Charter Member),MCSE+I (NT4.0), > > > > > > > MCSA (Charter Member), MCP+I, MCP(21), Inet+, Net+, A+ > > > > > > > Lead Technology Architect, TechTrain > > > > > > > Author: Cisco, The Complete Reference > > > > > > > http://www.alfageek.com > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=44492&t=44408 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
