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VLAN question. Access links vs trunk links

Posted on 2004-08-21
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Having trouble understanding the difference between Access Links and Trunk Links.  Trunk links are used to connect switches together when you're running VLANs on the switches correct?   When would you use Access Links?

Also, I have two 2924XL switches here running 11.2 (8) SA4 enterprise edition IOS.  Both switches are 4mb. I heard that you cannot do trunking on switches with 4mb. Is this true? Why would Cisco let you run an IOS on your switch, if the switch isnt capable of doing everything??

Thanks
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Question by:dissolved
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Expert Comment

by:lrmoore
ID: 11860099
Access links connect to hosts
Trunk links connect switches together.
There is no reason Enterprise OS will not allow trunking. The 4Mb, I assume, is the amount of memory. You can't use the newer 12.x OS. Still, all the original functions remain and trunking should not be a problem.
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by:Don Johnston
ID: 11860315
An access link is a port that can carry traffic for only one paticular VLAN. Whichever one was assigned to that port. Usually used on ports that connect to end stations, servers, routers. Can also be used on connections to switches (if only one VLAN is moving between the switches).

A trunk link is a port that can carry traffic for multiple VLAN's. Before exiting the switch, the frame gets identified as being associated with whichever VLAN it originates from. The receiving device reads that identifier and will only allow that frame to exit acces links that are members of that paticular VLAN. Typically used on links connecting to other switches, routers and even servers.

As long as you're running the Enterprise edition of the IOS, you can do either 802.1q or ISL trunking.

-Don
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Expert Comment

by:zubijalal
ID: 11860360
When you configure the interface mode to access,you connect host on that interface to switch.
When you configure the interface  mode to trunk that interface is used to connect the two switchs or a router to switch.Trunk link is used to carry the information for all the VLANS through the single link.

PC----access----switch-----trunk -----switch----trunk----router

You can configure the trunk without any issue.4MB is the memory installed on switch.
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Author Comment

by:dissolved
ID: 11860469
Thanks guys, made things much clearer.

Here is where I saw that you cant use 4mb switches for trunking
http://www.cisco.com/en/US/tech/tk389/tk390/technologies_tech_note09186a008017f86a.shtml#subtopic2h


Thanks again
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Expert Comment

by:MarkDozier
ID: 11863075
And it is true that the 2900 XL will not support Trunking with only 4 MB. Tha is becuase the 2900XL uses the Cat O?S, not the ciscio IOS. the CAT O/S is from older switches before cisco began putting the IOS on them.
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by:lrmoore
ID: 11863679
Interesting.  Never too late to learn something new!
Sounds like you got yourself a couple of good doorstops if your intent was to learn as much as you could about Cisco networking...
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Author Comment

by:dissolved
ID: 11864159
I'm not questioning you don, but how would I be able to tell if I'm running IOS or CatOS?

Here is a sh ver.  It says it is running cisco internetwork operating system software (IOS?)

2924a#sh ver
Cisco Internetwork Operating System Software
IOS (tm) C2900XL Software (C2900XL-HS-M), Version 11.2(8)SA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1998 by cisco Systems, Inc.
Compiled Mon 23-Nov-98 20:59 by paulines
Image text-base: 0x00003000, data-base: 0x00202144

ROM: Bootstrap program is C2900XL boot loader

2924a uptime is 1 day, 15 hours, 43 minutes
System restarted by reload
Running default software


cisco WS-C2924C-XL (PowerPC403GA) processor (revision 0x11) with 4096K/640K bytes of memory.
Processor board ID 0x09, with hardware revision 0x00
Last reset from warm-reset

Processor is running Enterprise Edition Software
23 Ethernet/IEEE 802.3 interface(s)

32K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address: 00:90:2B:BF:96:80
Configuration register is 0xF

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Expert Comment

by:Don Johnston
ID: 11864246
I didn't know there was a Catalyst O/S for the 2900xl's...

You're running IOS. Notice the first line of output from the show version "Cisco Internetwork Operating System Software".

Cat O/S versions of this vintage would be around 3.x or 4.x

-Don
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Author Comment

by:dissolved
ID: 11864265
Given the new found information, would I be able to do trunking?
thanks again
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Expert Comment

by:Don Johnston
ID: 11864358
Based on the information in your link above, I'd have to say no. You've only got 4MB of memory.

Out of curiosity, what happens when you try to configure trunking?

-Don
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Author Comment

by:dissolved
ID: 11864434
Damn. What do you recommend I do in regards to VLANs? Trying to learn. Is it possible to have a VLAN span to my 2nd switch? If so, how many?


I have not tried trunking yet, as my second switch has not arrived (will be here Tuesday. Had to return my other one, bad flash).

Thanks man
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Expert Comment

by:Don Johnston
ID: 11864526
If you can't do trunking, that doesn't mean you can't extend a VLAN to a second switch.

You can connect the two switches using multiple access links. One for each VLAN. Obviously, this isn't a great solution as you will need a switch-to-switch link for each VLAN.

-Don
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Author Comment

by:dissolved
ID: 11864593
So when I connect the two switches using multiple access links, I configure the actual ports that interconnect the switches as belonging to the same vlan?
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Accepted Solution

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Don Johnston earned 500 total points
ID: 11864990
Yes.

For example, let's say you have created 3 VLAN's on the two switches. You a various ports going to different devices in different VLAN's. To allow the three VLAN's on switch A to talk to the respective three VLAN's on switch B, you would need three seperate links between the two switches. Each in a seperate VLAN.

--------------                                ------------------
Switch A    |                               |     Switch B
             Port 1______________Port 1
             VLAN1                        VLAN1
                |                                |
             Port 2______________Port 2
             VLAN2                        VLAN2
                |                                |
             Port 3______________Port 3
             VLAN3                        VLAN3
                |                                |
-------------                                 -----------------

It ain't pretty, but it'll work.

-Don
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Author Comment

by:dissolved
ID: 11865109
Thanks man. Phew, thats a lot of crossover cables lol
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