Priscilla, I'm going to open my mouth wide in preparation for my size 11 foot. while I agree with your core message, I tend to believe that you may be looking at a "typical" modern network through rose colored glasses. For example, I have been working with 3 small/medium (700-1000+ hosts) sized networks recently. All 3 flat and all 3 suffering from excessive broadcasts.
I agree that in an "ideal" situation, the PCs have 1000Mhz+ processors, 100Mb full-duplex connections, and only IP across the wire. However, while a commendable vision, I just don't see it that way in the field. There are always older PCs on the network, substandard cabling, a myriad of protocols (typically from network printers operating with the default protocols), and/or other issues that just can't be easily and quickly fixed. In the cases of my clients previously mentioned, VLANs are the immediate cure. Priscilla, I surely mean absolutely no disrespect, so I guess we'll just have to agree to disagree that VLANs are still a good thing! Besides, I don't believe we can ever say they won't be useful but rather we'll just need fewer and fewer of them as the size of our well designed IP networks grow because of the reasons you already mentioned. Rik -----Original Message----- From: Chuck Larrieu [mailto:[EMAIL PROTECTED]] Sent: Wednesday, October 24, 2001 7:52 PM To: [EMAIL PROTECTED] Subject: RE: MAC address and VLANs [7:23950] hooray for you, PO! you are absolutely correct. In military science, it is well known that military establishments enter any war prepared to fight the previous one. In these days of DSL to the home desktop, 100 megabit to the office desktop, ATM backbone WANS, and HTML based applications, we networking students study various means of eking out another packet or two on 56K links. Anyone here see the point of ISDN backup for DS3 links? ;-> Your forward thinking is commendable. Chuck -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Priscilla Oppenheimer Sent: Wednesday, October 24, 2001 11:51 AM To: [EMAIL PROTECTED] Subject: Re: MAC address and VLANs [7:23950] The multi-VLAN feature that Leigh Anne mentioned might solve your problem. The Cisco switch port could be associated with two VLANs that way. You didn't say which switch you have, and this feature may not be available on all Cisco switches, though. Assuming that you don't want to upgrade the little switch to one that does 802.1Q or ISL, another somewhat radical fix to the problem might be to not use VLANs. My philosophy is that once VLANs get to the point of causing more problems then they fix, I eliminate them. ;-) One of the main things VLANs were supposed to fix was excessive broadcasts causing too many CPU interruptions on numerous workstations in a large, flat, switched network. Lately I have taken to making the controversial statement that this problem doesn't exist on many modern networks. These days workstations have amazingly fast CPUs. They are not bogged down by processing broadcasts. Also, as we eliminate older "desktop" protocols such as AppleTalk and IPX, what is still sending broadcasts? An ARP here or there is not a big problem. And ARPs don't actually happen that often. A PC keeps the data-link-layer address of its default gateway and other communication partners for a long time. Also, a lot of PC NICs used to be stupid about multicasts and interrupt the CPU for irrelevant multicasts for which the PC was not registered to listen. I bet that bug has been fixed by now. VLANs have other benefits (security, dividing up management and administrative domains, etc.) But if broadcasts are the issue, one should ask: Which protocol send broadcasts and how often? How fast are the CPUs? And that is my latest harangue against my least favorite LAN technology (VLANs!) Priscilla At 09:52 AM 10/24/01, NetEng wrote: >Thanks for the replies. The two MAC addresses would come from the two >PC's in an office. The would both connect in to a hub and then the hub >would uplink to the cisco switch. I need one pc in VLAN1 and one pc in >VLAN2, from >what you and Dennis stated this will not work. I appreciate the >comments though. > >Collin > >""Leigh Anne Chisholm"" wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > Actually, that's not correct. The original specification for VLANs > > from what I understand mandates that only one VLAN can be assigned > > to a port, >but > > manufacturers such as 3COM decided to do otherwise and support > > multiple VLANs per port. Cisco responded by creating (on certain > > switches such as > > the Catalyst 2900XL) an administrator to configure a port to be a > > member >of > > more than one VLAN at a time when using a membership mode known as > > "Multi-VLAN". A Multi-VLAN port can belong to up to 250 VLANs; the actual > > number of VLANs to which the port can belong depends on the > > capability of > > the switch itself. Although the concept is similar, this membership > > mode >is > > different than "trunking". The caveat to this feature is that the > > Multi-VLAN membership mode cannot be configured on a switch if one > > or more > > ports on the switch have been configured to trunk. > > > > For more information on this feature, search Cisco's website using > > the keyword phrase "switchport multi". > > > > As for answering NetEng's question--I can't quite determine where multiple > > MAC addresses share the same switch port. Could you identify which switch > > that is? > > > > > > -- Leigh Anne > > > > > -----Original Message----- > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On > > > Behalf Of Dennis > > > Sent: Tuesday, October 23, 2001 3:48 PM > > > To: [EMAIL PROTECTED] > > > Subject: Re: MAC address and VLANs [7:23950] > > > > > > > > > Cisco will recognize multiple macs on a single port but they must > > > all be in the same vlan. Vlan assignment is per port. Your other > > > option would be to > > > replace the non cisco hub with a cisco switch which is trunked to the >main > > > switch. > > > > > > -- > > > > > > -=Repy to group only... no personal=- > > > > > > ""NetEng"" wrote in message > > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > Here's my situtation. I have a corporate PC with an IP address > > > > of > > > 10.10.x.x > > > > and in the same office (and same physical network) another > > > device with an > > > IP > > > > address of 192.168.100.x Both devices are connected to a small > > > hub/switch > > > > which in turn is connected to a cisco switch. Can I have the > > > 10.10.x.x be > > > > apart of one vlan and the 192.168.100.x be a member of another > > > > or the > > > > default vlan? Can cisco switches recognize multiple MAC > > > > addresses on a > > > > single switch port (if so, how many?) and be smart enough to > > > > know >which > > > vlan > > > > which MAC address belongs to? This would save me hours > > > > (otherwise I >have > > > to > > > > run cable for connections to our corporate network and > > > connections to our > > > > test network in every cube :-( ). TIA > > > > > > > > PS I understand the best way to do this would be to connect each >device > > > into > > > > the cisco switch, but I only have a single cable run to each >cube/office > > > > > > > > > > > > (corporate pc)10.10.x.x > > > > | > > > > PC PC (test network) 192.168.100.x > > > > | | > > > > \ / > > > > \ / > > > > SWITCH/HUB (non-cisco) > > > > | > > > > | > > > > CISCO SWITCH > > > > VLANs > > > > -------- ---------- > > > > | | | | > > > > | corp | | test | > > > > -------- ----------- ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=24068&t=23950 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
