Full Duplex Issue on IOL

Published by Keyboard Banger on

eve-ng

Trying to configure duplex settings under an IOL switch interface can be a pain in the ass, especially when you are practicing RSTP and you need to have point-to-point links. You do “show spanning-tree” and you see that your interfaces are still “shared”, which don’t run RSTP:

VLAN0001
 Spanning tree enabled protocol rstp
 Root ID Priority 24577
 Address aabb.cc00.1000
 This bridge is the root
 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

 Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
 Address aabb.cc00.1000
 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
 Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/0 Desg FWD 100 128.1 Shr
Et0/1 Desg FWD 100 128.2 Shr
Et0/3 Desg FWD 100 128.4 Shr

The problem you could encounter is one of these two scenarios:

  • despite you are sure you did “duplex full” command under the interface level, you have “auto” when you do “show interface status”
  • when you type “duplex full” command, you get the following error: “Autoneg enabled. Duplex cannot be set.”

If you only have IOL images

A useful method to convert switch interface to full duplex modes and enjoy playing with RSTP is to:

  • use one of the Advanced Enterprise versions of IOL
  • under the desired switch interface
    • configure “duplex full”
    • configure “spanning-tree link-type point-to-point”
Switch-1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Switch-1(config)#
*Sep 1 21:56:37.819: %SYS-5-CONFIG_I: Configured from console by console
Switch-1(config)#int range e0/0 - 1 , e0/3
Switch-1(config-if-range)#spanning-tree link-type point-to-point

Now RSTP sees the interfaces as point-to-point and should be able to run on them:

Switch-1#sh spanning-tree

VLAN0001
 Spanning tree enabled protocol rstp
 Root ID Priority 24577
 Address aabb.cc00.1000
 This bridge is the root
 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

 Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
 Address aabb.cc00.1000
 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
 Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/0 Desg FWD 100 128.1 P2p
Et0/1 Desg FWD 100 128.2 P2p
Et0/3 Desg FWD 100 128.4 P2p

However, you’ll notice that:
* although you configured RSTP as the spanning-tree mode,
* although spanning tree seems to detect your switch interfaces as P2P,
The actual convergence times are those of a 802.1d STP.

So a better solution would be the second option, which is:

Use vIOS instead of IOL

I wanted to see if vIOS had the same limitations as the IOL in terms of RSTP, and I found:

  • the duplex issue is not present with vIOS

 

Switch#sh int status

Port      Name               Status       Vlan       Duplex  Speed Type
Gi0/0                        connected    1          a-full   auto RJ45
Gi0/1                        connected    1          a-full   auto RJ45
Gi0/2                        connected    1          a-full   auto RJ45
Gi0/3                        connected    1          a-full   auto RJ45
    • RSTP convergence times are real, and not of a regular 802.1d STP.
Switch#sh spanning-tree

VLAN0001
  Spanning tree enabled protocol rstp
  Root ID    Priority    32769
             Address     5000.0008.0000
             Cost        4
             Port        1 (GigabitEthernet0/0)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     5000.0009.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0               Root FWD 4         128.1    P2p
Gi0/1               Altn BLK 4         128.2    P2p
Gi0/2               Desg FWD 4         128.3    P2p
Gi0/3               Desg FWD 4         128.4    P2p

Switch#
Switch#debug spanning-tree switch state
Spanning Tree Port state changes debugging is on
Switch#
Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#int gi0/0
Switch(config-if)#shut
Switch(config-if)#
*Sep  1 22:40:34.328: STP SW: Gi0/2 new blocking req for 1 vlans
*Sep  1 22:40:34.328: STP SW: Gi0/3 new blocking req for 1 vlans
*Sep  1 22:40:34.329: STP SW: Gi0/1 new forwarding req for 1 vlans
*Sep  1 22:40:36.322: %LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to administratively down
*Sep  1 22:40:37.322: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down
*Sep  1 22:40:49.329: STP SW: Gi0/2 new learning req for 1 vlans
*Sep  1 22:40:49.330: STP SW: Gi0/3 new learning req for 1 vlans
*Sep  1 22:41:04.330: STP SW: Gi0/2 new forwarding req for 1 vlans
*Sep  1 22:41:04.331: STP SW: Gi0/3 new forwarding req for 1 vlans
Switch(config-if)#
Switch(config-if)#do sh spanning

VLAN0001
  Spanning tree enabled protocol rstp
  Root ID    Priority    32769
             Address     5000.0008.0000
             Cost        4
             Port        2 (GigabitEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     5000.0009.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Root FWD 4         128.2    P2p
Gi0/2               Desg FWD 4         128.3    P2p
Gi0/3               Desg FWD 4         128.4    P2p


Switch(config-if)#no shut
Switch(config-if)#
*Sep  1 22:41:55.172: STP SW: Gi0/0 new blocking req for 1 vlans
*Sep  1 22:41:55.181: STP SW: Gi0/1 new blocking req for 1 vlans
*Sep  1 22:41:55.182: STP SW: Gi0/2 new blocking req for 1 vlans
*Sep  1 22:41:55.182: STP SW: Gi0/3 new blocking req for 1 vlans
*Sep  1 22:41:55.183: STP SW: Gi0/0 new forwarding req for 1 vlans
*Sep  1 22:41:57.095: %LINK-3-UPDOWN: Interface GigabitEthernet0/0, changed state to up
*Sep  1 22:41:58.094: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up
*Sep  1 22:42:10.184: STP SW: Gi0/2 new learning req for 1 vlans
*Sep  1 22:42:10.185: STP SW: Gi0/3 new learning req for 1 vlans
*Sep  1 22:42:25.185: STP SW: Gi0/2 new forwarding req for 1 vlans
*Sep  1 22:42:25.186: STP SW: Gi0/3 new forwarding req for 1 vlans

Categories: Home Lab

Keyboard Banger

Keyboard Banger is a network engineer from Africa. He has been working in network support and administration since 2008. He started writing study notes about certification exams and technology topics a couple of years ago. When he's not writing articles, he can be found wandering on technical forums.

1 Comment

Willy · 23/09/2018 at 23:42

May I know the version of vios?

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