Wow.
# wc franks_response.txt
125 914 6386That's almost a 1,000-word essay. I'm speechless. :-) Mike On Thu, Sep 04, 2003 at 12:53:40PM -0600, Frank Sorenson wrote: > On Thu, 4 Sep 2003, Michael Ryan Byrd said: > > So we can go down to compUSA and buy a number of ethernet devices: > > > > 1- hub > > 2- hub/switch > > 3- switching Hub > > 4- switch > > > > Are 2,3 and 4 the same thing? Do these "switches" do Spanning Tree loop > > prevention like I presume the more expensive Cisco Catalyst switches do? > > > > What is the difference between an EtherFast 4124 24-Port 10/100 Ethernet Switch > > for $129.00 and $1825.00 Cisco catalyst 3524 xl ent ed feth 24 ports stackable > > switch? > > > > ideas? > > > > Ryan > > I'd guess 2, 3, and 4 are the same, but it sounds like marketing junk to > me. "I'll just put it's a switch or a hub, and more people will buy it > because it'll sound more versatile." > > Remember back to the OSI model. There are 7 Layers defined. Most of the > time, though, we just refer to the TCP/IP network model, which pretty > much just lumps layers 4-7 together: > > Layer 1 - Link (Physical for OSI) - This pretty much refers to just the > physical cable, and the electrical signals that go over it. This is where > you'd classify a hub. It just takes in signals from one port and > broadcasts those same signals across all the ports. In a pinch, you can > sometimes skip the hub completely and just wrap the wires together. > You'll get collisions, everyone "hears" the conversation, etc. The > Link/Physical layer acts as a bridge between physical networks. > > Layer 2 - Network (Data Link for OSI) - This refers to one layer of > interpretation of the electrical signals carried. The signals are > interpreted into data frames, and the source and destination MAC addresses > are deciphered. Switches work at this layer by determining the source and > destination, storing a table of MAC address to port translations, and > allowing computers on two ports to communicate directly. None of the > devices on other ports "hear" the conversation, and no extra bandwidth is > taken up for devices that aren't participating in the conversation. > > Layer 3 - Transport (Network for OSI) - At this level, the Network (or > Data Link) information is interpreted again, and the source and > destination IP addresses become important. A Network layer device acts as > a bridge between different IP networks, the public internet and your local > LAN, for example. I'd usually call one of these devices a router, but it > can be called a switch too, based on the functionality you're referring to > at the time. It maintains a routing table of IP addresses and ports, > rather than just the MAC addresses. > > Layer 4 - Application - This layer involves the TCP or UDP protocols on > top of everything else. If you've got a firewall that is blocking port 25 > (for example), that's operating at the Transport layer. > > On top of these layers, there's a lot of configuration that can go into > switches and routers. Some switches are engineered better than others, > and it can be difficult to compare two switches directly. Some switches > can be upgraded with newer firmware to fix bugs or provide new > functionality. > > Higher end switches generally have a configuration interface that allows > you to enable/disable a (physical) port, configure spanning-tree options, > change the port configuration (full/half duplex, 10/100 Mbps, etc.) or > remotely monitor port information and statistics. They may also support > trunking (aggregating several connections for extra bandwidth) or failover > (redundant links). Stacking switches often have very high speed links > between the switches in the stack, or have their own interface. The Cisco > 3524 uses high-speed uplinks between stacked switches. > > When switches are configured, it can be done in-band (such as over the > network) or out-of-band (separate serial port, for example). In-band can > be through telnet, an embedded web server, or through SNMP, for example. > > There are a number of ways in which a switch can be engineered, and these > engineering decisions can affect botht he price and the performance. > Ideally, every port could communicate at full-speed, full-duplex with > another port, and nothing would ever get dropped. In practice, though, > this makes for a lot of connections within the switch, and the engineering > for it can get difficult. > > Some switches utilize a bus to pass the signals from one port to another, > and some use a crossbar fabric. On a bus, one port just puts the packet > onto the wires, and it is rebroadcast by the correct port elsewhere on the > bus. A crossbar design allows multiple input ports to send messages to > multiple output ports simultaneously. Since shared-bus switches are order > n, and crossbar designs are n^2, the crossbar is often more complex and > expensive. > > Switches can also forward the packet immediately after determining the > destination MAC address, or they can read the whole thing into a buffer, > check the CRC, and then forward valid packets to the appropriate > destination. This store-and-forward is slower, but won't forward > corrupted frames. > > More expensive switches often have more or larger buffers, bigger MAC > address tables, or faster memory. > > To answer your original question a bit more, there is a big difference > between the Linksys EtherFast 4124 and the Cisco 3524 (though maybe not > $1700). Depending on what functions you need and use, you may or may not > notice the difference. > > For example, you can add 2 GBIC modules (gigabit expansion modules) to the > Cisco 3524, and it supports management functions and auxiliary VLANs. > The Linksys is not a managed switch, so you can't enable/disable ports, > change parameters, or monitor it. The Cisco is probably also engineered > better, and will probably support higher bandwidth between ports. > > In the CS Department, our main switch/router is an Alcatel OmniCore 5052: > http://www.alcatel.com/products/productsummary.jhtml?_DARGS=/common/opg/products/include/searchResults.jhtml.7_A&_DAV=/x/opgproduct/OmniCore_5052.jhtml > > We also have a number of smaller switches. They are a combination of: > > Alcatel OmniCore 5010's: > http://www.alcatel.com/products/productsummary.jhtml?_DARGS=/common/opg/products/include/searchResults.jhtml.7_A&_DAV=/x/opgproduct/OmniCore_5010.jhtml > > Cisco 3512 XL's and 3524 XL's (both EOL'd): > http://www.cisco.com/en/US/products/hw/switches/ps637/ps640/index.html > http://www.cisco.com/en/US/products/hw/switches/ps637/ps642/index.html > > Netgear FSM726S's: > http://www.netgear.com/products/prod_details.asp?prodID=122&view=sb > > and some other miscellaneous stuff. Our firewall (which also does some > routing) runs Linux. > > Other interesting links--- > > About the OSI and TCP/IP models: > http://www.ussg.iu.edu/usail/network/nfs/network_layers.html > > About switched ethernet: > http://netlab1.bu.edu/~staro/546projects/switchedethernet/proj/trans.htm > > About the Linksys 4124: > http://www.linksys.com/products/product.asp?grid=35&scid=39&prid=473 > > About the Cisco 3524: > http://www.cisco.com/en/US/products/hw/switches/ps637/products_data_sheet09186a00800925c5.html > > Frank > --------------------------------------------------------------------------- > Frank Sorenson - KD7TZK > CSR Computer Science Department > Brigham Young University > [EMAIL PROTECTED] > > > ____________________ > BYU Unix Users Group > http://uug.byu.edu/ > ___________________________________________________________________ > List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list -- ------------------------------------------- | --------------------- Michael Halcrow | [EMAIL PROTECTED] Developer, IBM Linux Technology Center | | What's another word for synonym? | ------------------------------------------- | --------------------- GnuPG Keyprint: 05B5 08A8 713A 64C1 D35D 2371 2D3C FDDA 3EB6 601D
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