Question

cisco swtich issue

Asked by: mikeleahy

i have 4 cisco switches. 1 and 2 are connected via gig connectors, 1 and 4 are connected via fibre, 3+4 are connected via gig. does this mean that all switches can talk to each other i.e. even though they are not all directly connected. also i am installing a ciso 2960G gig switch, how should this be added in i.e. by connection to one switch???

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Asked On
2007-04-18 at 04:47:38ID22518318
Tags

cisco

Topics

Cisco PIX Firewall

,

Computer Servers

,

Network Switches & Hubs

Participating Experts
5
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250
Comments
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Answers

 

by: donjohnstonPosted on 2007-04-18 at 05:25:15ID: 18931006

Assuming they are configured correctly, they can "talk" to each other.

You can connect anyway you want. That's the beauty of switches and spanning-tree.

 

by: manualvinPosted on 2007-04-18 at 06:01:36ID: 18931257

Ques:
does this mean that all switches can talk to each other i.e. even though they are not all directly connected.

Ans:
Yes, all switches can talk to each other as long as you daisy chain all of them together, e.g. Switch A connects to Switch B directly and Switch B connects to Switch C, Switch A is therefore connected to Switch C through Switch B.

Ques:
also i am installing a ciso 2960G gig switch, how should this be added in i.e. by connection to one switch???

Ans:
Yes, by connecting to any 1 of your 4 current cisco switches, this cisco 2960G gig switch can be connected to all of them.

Best Regards,
Alvin

 

by: vchintalapatiPosted on 2007-04-18 at 12:25:56ID: 18934355

it also depends on if you have vlans

 

by: jasonwilliams74Posted on 2007-04-18 at 13:52:14ID: 18935085

All will talk. cisco has a proprietary protocol that it uses that allow all switches to learn about their neighbors.

Plug in your new switch, pretty much anywhere and it will be able to talk to everyone else.

to see your other devices, connect to the command line on any of the cisco switches and type:

show cdp neighbors detail

that will show all your other devices connected

Gets more complex when you start talking about VLAN's, STP, VTP etc...

HTH.

 

by: mikeleahyPosted on 2007-04-19 at 00:35:06ID: 18937272

if i do sh cdp nei det will it just show its directly connected neighbors or everything

 

by: squallkill99Posted on 2007-04-19 at 21:59:11ID: 18944307

just directly cnnected neighbors

 

by: mikeleahyPosted on 2007-04-20 at 00:54:48ID: 18944759

if a pc on switch one wants to send a packet to a client on switch 4 and its not directly connected, how does it know to send the data to its neighbor switch for transfer on

 

by: squallkill99Posted on 2007-04-20 at 04:38:40ID: 18945483

switches build a list of mac address everytime i sees information. when the first frame enters the switch and it dossent know witch port to send it out on it floods all ports except the origionateing port with the frame and puts the sendig mac address on its table. when the destination computer responds it adds its mac address to the table then after that it knows what port to send the information out on based on the information on that mac address table.

 

by: mikeleahyPosted on 2007-04-20 at 05:55:42ID: 18945908

ok but what if its ona different switch.are the mac addres tables shared between the switches

 

by: jasonwilliams74Posted on 2007-04-20 at 06:45:49ID: 18946272

No, MAC's are not shared amongst switches.
Each switch has its on MAC address table that it maintains. Doesn't share them across other switches.

Unless somethings has changed.... :)

HTH

 

by: mikeleahyPosted on 2007-04-20 at 07:13:51ID: 18946514

so, if a pc on switch 1 wants to send packets to a pc on switch 4. the switch one wont have the mac address of the destination so how will switch 1 know to send the packet to switch 4 and not switch 2 or does it flood all the switches

 

by: donjohnstonPosted on 2007-04-20 at 07:45:01ID: 18946798

At some point, it will see traffic from the PC coming in the port that happens to be connected to the other switch. In the MAC address table, there will be multiple MAC addresses associated with that port since there are multiple PC's connected to the switch that is connected to that port.

 

by: squallkill99Posted on 2007-04-20 at 11:42:34ID: 18948620

yes switches do share mac address (or at least cisco switches do)

 

by: jasonwilliams74Posted on 2007-04-20 at 12:12:00ID: 18948821

This is how I interpret this works:

Switch1 will add the Source MAC from PC1 into its MAC table. Since the Destination MAC is not directly connected (destination MAC is not listed in Switch1's MAC table), Switch1 will flood out all ports except the port from which it was received.

Switch2 will receive the frame with the PC1 MAC address, add the MAC (Source MAC) to its MAC table, flood out all ports except the port from which it was received since the destination MAC is not in Switch2's MAC table either.

The same process occurs in Switch3.

Switch4 receives the frame, adds the source MAC address (PC1) to its MAC table, examines the destination MAC (PC4) and doesn't have an entry so it floods the frame out all ports except the port from which it was received. PC4 receives the frame and responds by sending a frame to Switch4. As usual, Switch4 adds the Source MAC (PC4) to its MAC table. The destination MAC (PC1) was added to the MAC table of switches 1-4 already so the frame is forwarded to the specific port listed in the MAC table of each switch until it reaches PC1.

I hope that makes sense

 

by: squallkill99Posted on 2007-04-20 at 12:29:05ID: 18948944

agreed

 

by: donjohnstonPosted on 2007-04-20 at 14:02:37ID: 18949584

>yes switches do share mac address (or at least cisco switches do)

Actually, they don't.

20120131-EE-VQP-002

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