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ARP broadcasts not reaching all VLAN ports on 3550

wes-nanoboy
Level 1
Level 1

‎05-18-2013 04:07 AM - edited ‎03-07-2019 01:25 PM

Hello,

I have a weird problem and need your advice.

Cisco 3550, interface Vlan9

ip address 1.1.1.1 255.255.255.240 secondary

ip address 3.3.3.3 255.255.255.240

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

9    VLAN0009                         active    Fa0/1, Fa0/3, Fa0/5, Fa0/9

When I ping a (not set up) IP e.g. 1.1.1.100

I can see ARP requests coming to servers connected to 2 of the 4 ports

but no arp is coming to the other 2 machines (same hardware, same OS).

All 4 interfaces are configured identical way.

'debug arp' shows ARP is sent to vlan9:

switch 99: May 17 10:45:22.163 UTC: IP ARP: sent req src 1.1.1.1 0012.d95c.0532,

switch 100:                  dst 1.1.1.100 0000.0000.0000 Vlan9

I was expecting ARP broadcast to reach all ports of a VLAN - right?

What can be the cause?

Thank you in advance

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0 Helpful
5 Replies 5

antonio.guirado
Level 3
Level 3

‎05-18-2013 06:59 AM

Hello,

a VLAN is a broadcast domain. All ports in a vlan in forwarding state must forward the broadcast. Are you sure

that all ports are in STP forwarding state?.

Could send us the "show interfaces switchports" command output and "show spanning-tree vlan 9"

command?.

Regards

0 Helpful

wes-nanoboy
Level 1
Level 1
In response to antonio.guirado

‎05-18-2013 07:30 AM

Thank you for reply.

In the meantime I upgraded IOS to 12.2(44)SE6 and changed the vlan from 9 to 5. But the behaior did not change. Output for the vlan 5 ports:

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

5    VLAN0005                         active    Fa0,1, Fa0/3, Fa0/5, Fa0/9, Fa0/11

* I can see arp packets coming to devices connected to ports Fa0/3 and Fa0/11

* no ARP requests comes to Fa0/5, Fa0/9

* Device connected to Fa0/1 is offline

#show spanning-tree vlan 5

VLAN0005

  Spanning tree enabled protocol ieee

  Root ID    Priority    32773

             Address     0012.d96b.0680

             This bridge is the root

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32773  (priority 32768 sys-id-ext 5)

             Address     0012.d96b.0680

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Fa0/1               Desg FWD 100       128.1    P2p Edge

Fa0/3               Desg FWD 19        128.3    P2p Edge

Fa0/5               Desg FWD 19        128.5    P2p Edge

Fa0/9               Desg FWD 19        128.9    P2p Edge

Fa0/11              Desg FWD 19        128.11   P2p Edge

#show interfaces switchport

Name: Fa0/3

Switchport: Enabled

Administrative Mode: static access

Operational Mode: static access

Administrative Trunking Encapsulation: negotiate

Operational Trunking Encapsulation: native

Negotiation of Trunking: Off

Access Mode VLAN: 5 (VLAN0005)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk associations: none

Administrative private-vlan trunk mappings: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

Name: Fa0/5

Switchport: Enabled

Administrative Mode: static access

Operational Mode: static access

Administrative Trunking Encapsulation: negotiate

Operational Trunking Encapsulation: native

Negotiation of Trunking: Off

Access Mode VLAN: 5 (VLAN0005)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk associations: none

Administrative private-vlan trunk mappings: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

Name: Fa0/9

Switchport: Enabled

Administrative Mode: static access

Operational Mode: static access

Administrative Trunking Encapsulation: negotiate

Operational Trunking Encapsulation: native

Negotiation of Trunking: Off

Access Mode VLAN: 5 (VLAN0005)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk associations: none

Administrative private-vlan trunk mappings: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

Name: Fa0/11

Switchport: Enabled

Administrative Mode: static access

Operational Mode: static access

Administrative Trunking Encapsulation: negotiate

Operational Trunking Encapsulation: native

Negotiation of Trunking: Off

Access Mode VLAN: 5 (VLAN0005)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk associations: none

Administrative private-vlan trunk mappings: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

0 Helpful

antonio.guirado
Level 3
Level 3
In response to wes-nanoboy

‎05-18-2013 08:24 AM

Hello again,

all seems right. Can you ping from/to hosts that are in ports where arp are supposed not to be forwarded?.

Is it only that you do not see the broadcast in this ports? or is there a real connectivity problem?.

Regards.

0 Helpful

paul driver
VIP
VIP

‎05-18-2013 09:13 AM

hello

ping the broadcast address of the vlan -tjen those that are active.will reply

ping x.x.x.255

res
paul

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Kind Regards
Paul
0 Helpful

wes-nanoboy
Level 1
Level 1
In response to paul driver

‎05-18-2013 11:36 AM

Uff, I found it. It was related to IPMI. IPMI interface was set to 'Dedicated'.
When I switched it to 'Failover' (default setting) ARP requests reapperaed.
So looks like IPMI was taking over ARP requests and thus tshark/kernel not getting its payload.

A bit weird because the properly working hosts still have 'dedicated' set as IPMI NIC.

Maybe it will help someone.
Thank you all who tried to help

0 Helpful
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