Why the last port of two catalyst 3560X are connected together?

[gramesh12]

Hi,

I am a newbie here. We have two catalyst 3560X 24T-S switches connected on two separate LANs (both the networks are redundant to each other).

The last port of the switches are connected together? Please tell me what for it is done?

Regards

[Ivan Shirshin]

Hi Gunda,

Could you send the ports configuration from both switches?

Since you mentioned redundancy, could it be that this port connection ensures reachbility through another switch, should the local network connectivity fail?

Kind Regards,
Ivan

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[Leo Laohoo · Accepted solution]

I think this is what you are looking for:

Configuring 802.1Q Trunking Between a Catalyst 3550/3560/3750 and Catalyst Switches That Run Cisco IOS Software

Please don't forget to rate our useful posts.  Thanks.

Configuring InterVLAN Routing and ISL/802.1Q Trunking on a Catalyst 2900XL/3500XL/2950 Switch Using an External Router

[gramesh12]

Hi leolaohoo

thanks for your reply, I think you are right, it is something to do with trunking. I am yet to go thru the link you supplied. In short what for trunking is applied, please tell me.

Regards

[gramesh12]

Hi Ivan

thanks for your reply. Please tell me how to obtain the ports configuration, so that I can post the details?

Secondly  what I mean by the networks redundant to each other in my original post  is, on the hosts connected to these switches both the ports are teamed via Intel Motherboard configuration.

[Ivan Shirshin · Accepted solution]

Hi Gunda,

The command to check the interface configuration is "show run int ".

Kind Regards,
Ivan

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[gramesh12]

Hi Ivan

the output of the command show run int Gi0/24 is

!

interface GigabitEthernet 0/8

switchport trunk encapsulation dot1q

switchport mode trunk

srr-queue bandwidth share 1 30 35 5

queue set 2

priority-queue out

mls qos trust cos

macro description cisco-switch

auto qos trust

spanning-tree link type point-to-point

end

The same configuration is appearing on Gi0/8.

I happened to check the switch thru CNA, it shows under Switching / VLANS

Port no.          Admin mode           Operational mode            VLANS

8                    802.1Q Trunk               802.1Q Trunk                  ALL

24                  802.1Q Trunk               802.1Q  Trunk                 ALL

All other          Dynamic Auto               Static Access                1

ports

Regards

[Ivan Shirshin]

Hi Gunda,

This confirms the suggestion from before, the port is a trunk between switches as leolaohoo suggested.

You already confirmed the same via CNA - Operational mode is a trunk for all vlans.

Kind Regards,
Ivan

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[gramesh12]

Hi Ivan

thnaks, can you please tell me what is the requirement/advantage of doing this?

[Ivan Shirshin · Accepted solution]

Hi Gunda,

Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.

For example, if you have 2 different connections from switches to WAN or other LANs, in case WAN connection on switch A fails, the reachability in vlan to WAN will be available through WAN connection on switch B. Traffic from switch A will be passing to switch B via trunk link.

The link shared by leolaohoo is quite good for understanding how a trunk works, I suggest to check it if you have configuration/

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.1E/native/configuration/guide/layer2.html#wp1020409

Also see this book:

http://www.ciscopress.com/articles/article.asp?p=29803&seqNum=3

Kind Regards,
Ivan

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[gramesh12]

Ivan Shirshin wrote:
Hi Gunda,
Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network. 
For example, if you have 2 different connections from switches to WAN or other LANs, in case WAN connection on switch A fails, the reachability in vlan to WAN will be available through WAN connection on switch B. Traffic from switch A will be passing to switch B via trunk link.
The link shared by leolaohoo is quite good for understanding how a trunk works, I suggest to check it if you have configuration/
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.1E/native/configuration/guide/layer2.html#wp1020409
Also see this book:
http://www.ciscopress.com/articles/article.asp?p=29803&seqNum=3
Kind Regards, 
Ivan 
 
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Hi Ivan

sorry, I was away and could not see your reply immediately.

thanks a lot for your answer, that was a short & sweet reply and to the point. I will definitely go thru these links.

sorry to trouble you with some more questions:

1. The trunking on 24 th port is understandable , then why on 8th port also it is deifned?

2. Are the network modules used for increasing the reach of the LAN?

Regards

G.Ramesh.

[Ivan Shirshin]

Hi Ahmed,

Glad it was helpful!

In regards to your questions:

1. I understand from your previous explanation that this pair of switches are connected only on the last port 24.

That means the port 8 connects to another node and port 8 is a means to extend your vlans over 3rd switch.

2. When you install a network services module in a  Catalyst 3560-X or 3750-X switch, you can configure the 1-Gigabit and  10-Gigabit Ethernet uplink ports for the same features as any other  ports in the switch. So it also could be configured as trunk.

Kind Regards,
Ivan

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[gramesh12]

Ivan Shirshin wrote:
Hi Ahmed, 
Glad it was helpful! 
No it is Ramesh not Ahmed 


In regards to your questions:

1. I understand from your previous explanation that this pair of switches are connected only on the last port 24. 
That means the port 8 connects to another node and port 8 is a means to extend your vlans over 3rd switch.

2. When you install a network services module in a  Catalyst 3560-X or 3750-X switch, you can configure the 1-Gigabit and  10-Gigabit Ethernet uplink ports for the same features as any other  ports in the switch. So it also could be configured as trunk.

Uplink ports means for stacking or for extending LAN?

Kind Regards, 
Ivan 
 
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Regards

Ramesh

[Ivan Shirshin · Accepted solution]

HI Ramesh,

My bad, sorry for mistake  - I was looking at another post while typing and messed up the names :$

Stack ports is a separate entity. Uplink ports are the port on network ports. They are called so because network modules are often called "uplink network modules" and used for connecting to higher level of the network (e.g. to core or aggregation switch).

Kind Regards,
Ivan

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[gramesh12]

Ivan Shirshin wrote:
HI Ramesh, 
My bad, sorry for mistake  - I was looking at another post while typing and messed up the names :$
It's ok. 
Stack ports is a separate entity. Uplink ports are the port on network ports. They are called so because network modules are often called "uplink network modules" and used for connecting to higher level of the network (e.g. to core or aggregation switch).

Thanks for the info

Kind Regards, 
Ivan 
 
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Regards

Ramesh