Solved

Alternate/Backup Port

Posted on 2016-08-20
14
83 Views
Last Modified: 2016-08-21
I am trying to understand  in which scenario Alternate/Backup Ports can be used.
http://www.9tut.com/rapid-spanning-tree-protocol-rstp-tutorial
on the above Link they give example of a HUB , but I do not think anyone uses a Hub nowadays. However what if instead of a HUB as shown on the Link, we put  SwitchX with 2 uplinks connected to SW2
SwitchX is connect to other Downstream LAN

sw
0
Comment
Question by:jskfan
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
14 Comments
 
LVL 80

Assisted Solution

by:David Johnson, CD, MVP
David Johnson, CD, MVP earned 50 total points
ID: 41764027
with a switch wouldn't you want 1 port to sw2 and one to sw3.. This will give you redundancy if sw2 goes offline.
0
 
LVL 18

Assisted Solution

by:Garry Glendown
Garry Glendown earned 50 total points
ID: 41764064
Using multiple links between two switches makes sense (mainly) to either increase capacity (ensure you are using some sort of aggregation protocol like LACP instead of spanning tree), or if you physically (or due to commercial restraints) can run a ring link to another switch, but have different cable routings between the two devices. Otherwise, as David stated, you will split the network if the whole switch in between goes down.
Apart from that, when running a whole ring do make sure you have your loop prevention protocol (ST, RST, PVST, ...) set up uniformly between all devices, otherwise you will quickly notice ;)
0
 
LVL 29

Expert Comment

by:Predrag Jovic
ID: 41764067
Backup and alternative ports are port roles in RSTP.
Alternative port is port in discarding state and it is just another potential path to the root bridge. If some of the currently active paths to the root bridge becomes unavailable port will change state to forwarding and become new designated port or root port depending on what link on your topology drawing gets broken.
Backup port is port in discarding state that is connected to the shared network segment (like hub - so you will rarely see these today).

You can read Cisco's explanation - Understanding Rapid Spanning Tree Protocol (802.1w)

It is more interesting with this topology:
RST port roles
0
NEW Veeam Agent for Microsoft Windows

Backup and recover physical and cloud-based servers and workstations, as well as endpoint devices that belong to remote users. Avoid downtime and data loss quickly and easily for Windows-based physical or public cloud-based workloads!

 
LVL 46

Assisted Solution

by:Craig Beck
Craig Beck earned 50 total points
ID: 41764068
This is theoretical guys, just for learning and understanding how STP works.  :-)

Sometimes you cant connect to two different switches.

Using a switch would only really offer performance enhancements in this scenario as you can largely control STP functionality at SW2, as would be the case if the switch was unmanaged,for example.

In your scenario you'd have a DP at SW2 which would be a RP at the new switch (assuming it's managed) and the second port would be a DP at SW2 and a AP at the new switch.

A backup port would be where a redundant link is connected to the same hub and would replace the RP if it failed, after following the transition states, while an AP is a link that can immediately take over from the RP if it fails. A BP doesn't immediately transition into the RP as N AP does.
0
 
LVL 29

Expert Comment

by:Predrag Jovic
ID: 41764200
I forgot to mention above - backup port is always located on switch with designated port (as it can be seen on above picture (taken from Juniper site)).
0
 

Author Comment

by:jskfan
ID: 41764231
Craig Beck
This is theoretical guys, just for learning and understanding how STP works.  :-)

Correct..

It is hard to Master one thing while you are doing Other things
0
 

Author Comment

by:jskfan
ID: 41764233
Well, Alternate Port is just Blocking Port in STP
The gray area is the Backup Port, since HUBs are no longer used nowadays... Just thought to throw this question to see if Backup Ports are used in any other scenario than HUBs
0
 

Author Comment

by:jskfan
ID: 41764276
If you turn off STP on one Switch that is connected to another switch with 2 links. the other Switch will have one Forwarding Port and one Backup Port. Because when you turn off STP on a Switch , it will operate as a HUB
0
 
LVL 29

Accepted Solution

by:
Predrag Jovic earned 350 total points
ID: 41764283
Well, Alternate Port is just Blocking Port in STP
Basically, yes, that would be blocked port in STP.
The gray area is the Backup Port, since HUBs are no longer used nowadays...
Blue circle around B, but can look gray on some displays.
Because when you turn off STP on a Switch , it will operate as a HUB
If STP is turned off on the switch - it will still operate as switch (each port is separate collision domains). To turn switch to hub you need to turn off MAC learning on ports (ports in the same VLAN with MAC learning turned off are one collision domain).
0
 
LVL 57

Expert Comment

by:giltjr
ID: 41764284
Although HUB are not used today, some inexpensive switches don't support STP so the will produce loops within a network just like a HUB.
0
 
LVL 29

Expert Comment

by:Predrag Jovic
ID: 41764287
Additionally, to really function as HUB also ports on the switch should be configured in half duplex mode (forgot it above and comment is not editable anymore).
0
 

Author Comment

by:jskfan
ID: 41764349
So to Make a Switch works as a HUB.
-Turn off STP
- execute this command : no mac address-table learning vlan #
-configure each connected port to be Half Duplex
0
 
LVL 29

Expert Comment

by:Predrag Jovic
ID: 41764360
Yes.
MAC address learning can be also disabled per port:
no mac-address-table learning interface <type> <port>
0
 

Author Closing Comment

by:jskfan
ID: 41764366
Thank you Guys !
0

Featured Post

Manage your data center from practically anywhere

The KN8164V features HD resolution of 1920 x 1200, FIPS 140-2 with level 1 security standards and virtual media transmissions at twice the speed. Built for reliability, the KN series provides local console and remote over IP access, ensuring 24/7 availability to all servers.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
HP 1920 Switch -- IFNET LINK_UPDOWN Errors 3 80
Cisco SSLVPN webpage is not loading 3 30
Cisco To Cisco Trunk not working 2 25
Cisco SRST questions 5 20
Tired of waiting for your show or movie to load?  Are buffering issues a constant problem with your internet connection?  Check this article out to see if these simple adjustments are the solution for you.
I recently attended Cisco Live! in Las Vegas, a conference that boasted over 28,000 techies in attendance, and a week of hands-on learning hosted by a solid partner with which Concerto goes to market.  Every year, Cisco displays cutting-edge technol…
Both in life and business – not all partnerships are created equal. As the demand for cloud services increases, so do the number of self-proclaimed cloud partners. Asking the right questions up front in the partnership, will enable both parties …
As a trusted technology advisor to your customers you are likely getting the daily question of, ‘should I put this in the cloud?’ As customer demands for cloud services increases, companies will see a shift from traditional buying patterns to new…

740 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question