Trunking

Hi Brian,
I tried to simulate the same the same LAB in GNS3 as discussed in Advanced Technologies Class. I have an observation that when the trunk is ISL, I couldn't see the ARP entries for vlan 10 on all the switches. But if the trunk is 802.1q, I could see the ARP entries for all the switches and I'm able to ping them.

SW1#show interfaces trunk
Port Mode Encapsulation Status Native vlan
Gi0/0 auto n-isl trunking 1
Gi0/1 auto n-isl trunking 1
Gi0/2 auto n-isl trunking 1
Gi0/3 auto n-isl trunking 1
Gi1/0 auto n-802.1q trunking 1
Gi1/1 auto n-802.1q trunking 1

SW1#show run int vlan 10
Building configuration...
Current configuration : 61 bytes
!
interface Vlan10
ip address 10.10.10.1 255.255.255.0
end

SW2#show run int vlan 10
Building configuration...

Current configuration : 61 bytes
!
interface Vlan10
ip address 10.10.10.2 255.255.255.0
end

SW3#show run int vlan 10
Building configuration...

Current configuration : 61 bytes
!
interface Vlan10
ip address 10.10.10.3 255.255.255.0
!
SW4#show run int vlan 10
Building configuration...

Current configuration : 61 bytes
!
interface Vlan10
ip address 10.10.10.4 255.255.255.0

SW1#show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.1 - 0000.ab3a.800a ARPA Vlan10
Internet 10.10.10.3 0 Incomplete ARPA
Internet 10.10.10.4 49 0000.ab20.800a ARPA Vlan10

SW1#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24586
Address 0000.ab3a.2500
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
Address 0000.ab3a.2500
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 Desg FWD 4 128.1 Shr
Gi0/1 Desg FWD 4 128.2 Shr
Gi0/2 Desg FWD 4 128.3 Shr
Gi0/3 Desg FWD 4 128.4 Shr
Gi1/0 Desg FWD 4 128.5 Shr
Gi1/1 Desg FWD 4 128.6 Shr

SW2#show spanning-tree vlan 10

VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24586
Address 0000.ab3a.2500
Cost 4
Port 1 (GigabitEthernet0/0)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0000.ab45.1800
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 Shr
Gi0/1 Altn BLK 4 128.2 Shr

SW3#show spanning-tree vlan 10

VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24586
Address 0000.ab3a.2500
Cost 4
Port 3 (GigabitEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0000.ab6a.1100
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type


Gi0/2 Root FWD 4 128.3 Shr
Gi0/3 Altn BLK 4 128.4 Shr

SW4#show spanning-tree vlan 10

VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24586
Address 0000.ab3a.2500
Cost 4
Port 5 (GigabitEthernet1/0)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0000.ab20.a600
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type


Gi1/0 Root FWD 4 128.5 Shr
Gi1/1 Altn BLK 4 128.6 Shr

I have seen no issues with STP for vlan 10 with SW1 as root. I see ARP entry only for SW4 address and it is 802.1q trunk not ISL. Could you please confirm what is the issue.

IOS version: Version 15.2(4.0.55)E

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