12-27-2011 02:48 PM - edited 03-07-2019 04:04 AM
Hi,
I am studying CCNA 3 Lan Switching.
I have a question about the multiple trunk links that show up in my study notes.
Throughout the notes it explains about the trunk link betwenn switches, which i understand that once STP kicks in one of these links will be blocked.
When I go to the packet tracer sample exercises the switches now have 2 trunk links between each switch.
Can someone explain why the jump to 2 links??
Would STP then block 3 of the trunk links and leave one open?
I have attached an image of what I mean.
Thanks guys!!
12-27-2011 02:58 PM
Hi,
Usually when there are 2 links, you create an Etherchannel (bundle the links together) to get higher bandwidth. You can put up to 8 physical links in an Etherchannel.
http://www.cisco.com/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094bc5.shtml
HTH
12-27-2011 03:01 PM
Hi,
I was thinking that, but there is no mention of creating the 2 links to etherchannel in the packet tracer or even how to configure it.
Could there be any other purpose for the 2 links or am I just misinterpreting it?
12-27-2011 03:51 PM
I think, it is Etherchannel. It is pretty common for access layer switches to uplink to the Distro and core via Etherchannels.
What book is that?
HTH
12-27-2011 04:05 PM
Hi,
Its the Cisco Networking academy online study material, Exploration 3.
I will re-read my labs, to see if there is mention of etherchannel in the one with multiple trunks in that particular lab.
What would happen if you configured 2 trunk links on the same switch with the same VLAN's does it automatically become an etherchannel? Just thinking its a bit strange if it is etherchannel as there is no real reference to configure it in the notes.
I found a mention of it in the notes
hopefully its ok to post it here...
"
Redundant links are configured in the form of an EtherChannel that protects against a single link failure. Cisco EtherChannel technology enables you to aggregate multiple physical links into one logical link. This can provide up to 80 Gb/s of aggregate bandwidth for with 10 Gigabit EtherChannel. "
But then it goes on to say that etherchannel is a CCNP topic... so it doesnt give any config examples or anything like that.
Its really puzzling me now... why would there be etherchannel in the labs if there is no guidance on configuring it?
If its of any use the 4 trunk links coming from the 1st switch in the lab are all set to be native.
12-27-2011 04:11 PM
What would happen if you configured 2 trunk links on the same switch with the same VLAN's does it automatically become an etherchannel?
No it won't. If you have two (or more) trunk links coming-and-going to a pair of switches it's good practice to put them in etherchannel.
12-27-2011 04:12 PM
No, that will not happen. You have to configure the Etherchannel or Portchannel manually, then add the physical links to it, then use LACP, PAGP, or On on both sides of the link. It is not automated.
Have a look at this config guide to get more details on how to configure a Portchannel
HTH
12-27-2011 05:48 PM
If its of any use the 4 trunk links coming from the 1st switch in the lab are all set to be native.
I have no problem with the configuration of these links, I was just looking for a reason why there would be 2 from a single switch going to another single switch. I understand the redundancy issue & why you need to have multiple paths etc, its just the 2 trunk link thing thats throwing me. I know this will annoy me if I cant understand why they are there.
here is the config of the links.
interface FastEthernet0/1
switchport trunk native vlan 99
switchport mode trunk
!
interface FastEthernet0/2
switchport trunk native vlan 99
switchport mode trunk
!
interface FastEthernet0/3
switchport trunk native vlan 99
switchport mode trunk
!
interface FastEthernet0/4
switchport trunk native vlan 99
switchport mode trunk
!
interface FastEthernet0/5
switchport trunk native vlan 99
switchport mode trunk
Theres no mention of etherchannel there either.
12-27-2011 06:08 PM
I understand the redundancy issue & why you need to have multiple paths etc, its just the 2 trunk link thing thats throwing me. I know this will annoy me if I cant understand why they are there.
Must be an old book.
12-27-2011 06:19 PM
its not a book, its the current online study for CCNA , maybe they are just there for illustration purposes to get you into the idea of there being 2 links (that later should be configured as etherchannel once you reach the CCNP level). Maybe I am looking too much into this...was something I spotted in the lab work & wanted to run past the folk on this forum.
Thanks for your help with this much appreciated.
Cheers
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