Arp request failed

Unanswered Question
Aug 20th, 2010

Hi all,

I 'm experiencing a very strange  situation regarding arp.

My topology :

<--router vlan Y C3750 router  vlan X--> C2960G --> C3020--> Client 1

Client 1 is connect to a C3020 switch in vlan X and is trying to reach his default gateway using icmp

Client 1 sent arp request ( who is on vlan X interface ( hsrp)) but never receive answer . So it cannot join his default gateway.

When I connect a client 2 on C2960G in the same vlan X, then client 1 is now able to ping his default gateway because it"s now receiving the arp response from the default gateway. If I remove the Client 2 from the C2960, the client 1 lose the connection to the gateway.

At this time, the arp request is never arriving to the 3750 excepted when the client 2 is back on C2960G

Can some help me to solve the issue. This append for new vlan X not for other vlans already in  use.

Also, client 1  can ping all other computer in the vlan excepted his default gateway.

vlan x is well forwarded up to the C3020.

vlan x is defined everywhere

Thanks a lot.

Regards.

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
shahhardik Fri, 08/20/2010 - 02:41

Hi Riziv,

Hey i'm not expert to ans your query, but still i want to know; do you have any other system connected to same Vlan X on 2960? If no then can you check your Vlan X status before and after connecting your client 2 on 2960. Because i think when you dont have any system physically connected on your Vlan, till that time particular Vlan stays in Down state.( i.e. down down)

Experts! please correct me if i'm directing Riziv in wrong direction.

Regards,

Hardik

riziv Fri, 08/20/2010 - 02:52

Hi Hardik,

Thanks for your reply.

Yes, the vlan is in active state as well as when Client 2 is connected on or not.

show vlan output:

41  xxxxxxx      active

Thanks a lot.

Regards.

KARUPPUCHAMY MA... Fri, 08/20/2010 - 02:59

Hi,

As per your statement // Also, client 1  can ping all other computer in the vlan excepted his default gateway.//

To ping other computers are in the same vlan, no need to reach the default gateway.

can you paste the output of the below commands of all your switches.something we need to look C3020 configuration,

#sh vlan id

#sh int trunk

#sh vtp status

#sh spanning-tree

Thanks

Samy

riziv Fri, 08/20/2010 - 03:24

Hi Samy,

I know that there 's no need to join the gateway when on the same subnet. but it proves that the vlan is well forwarded on the switches as another client located on the same vlan in another branch of the network can reach client1.

here is the output of the commands:

Note that Distri1-CPR-C67 is the 2960 switch and SW-BLADE1 is the 3020 switch

The issue is on vlan 41

Distri1-CPR-C67#sh spanning-tree  vlan 41

VLAN0041
  Spanning tree enabled protocol rstp
  Root ID    Priority    4137
             Address     0024.13b5.c080
             Cost        4
             Port        21 (GigabitEthernet0/21)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32809  (priority 32768 sys-id-ext 41)
             Address     0024.5153.c980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- ----------------------------
Gi0/21              Root FWD 4         128.21   P2p
Gi0/22              Altn BLK 4         128.22   P2p
Po1                 Desg FWD 3         128.56   P2p
Po2                 Desg FWD 3         128.64   P2p
Po3                 Desg FWD 3         128.72   P2p
Po4                 Desg FWD 3         128.80   P2p


Distri1-CPR-C67#sh int trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/21      on               802.1q         trunking      1
Gi0/22      on               802.1q         trunking      1
Po1         on               802.1q         trunking      1
Po2         on               802.1q         trunking      1
Po3         on               802.1q         trunking      1
Po4         on               802.1q         trunking      1

Port        Vlans allowed on trunk
Gi0/21      1,9,11-12,14-15,40-46
Gi0/22      1,9,11-12,14-15,40-46
Po1         1,9,11-12,14-15,40-41
Po2         1,9,11-12,14-15,40-41
Po3         1,9,11-12,14-15,40-41
Po4         1,9,11-12,14-15,40-41

Port        Vlans allowed and active in management domain
Gi0/21      1,9,11-12,14-15,40-46
Gi0/22      1,9,11-12,14-15,40-46
Po1         1,9,11-12,14-15,40-41
Po2         1,9,11-12,14-15,40-41
Po3         1,9,11-12,14-15,40-41
Po4         1,9,11-12,14-15,40-41

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/21      1,9,11-12,14-15,40,42-46
Gi0/22      none
Po1         1,9,11-12,14-15,40-41
Po2         1,9,11-12,14-15,40-41
Po3         1,9,11-12,14-15,40-41
Po4         1,9,11-12,14-15,40-41
Distri1-CPR-C67#

Distri1-CPR-C67# sh vtp status
VTP Version                     : running VTP2
Configuration Revision          : 10
Maximum VLANs supported locally : 255
Number of existing VLANs        : 17
VTP Operating Mode              : Client
VTP Domain Name                 : CPR1
VTP Pruning Mode                : Enabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Enabled
MD5 digest                      : 0xC4 0xC1 0x3A 0xA3 0x37 0x93 0x9F 0xD3
Configuration last modified by 10.14.2.3 at 8-13-10 08:21:44

Distri1-CPR-C67#sh vlan id 41

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
41   NLB_exchange                     active    Gi0/21, Gi0/22, Po1, Po2, Po3
                                                Po4

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
41   enet  100041     1500  -      -      -        -    -        0      0

Remote SPAN VLAN
----------------
Disabled

Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------


SW-BLADE1#sh int trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/1       on               802.1q         trunking      1
Gi0/2       on               802.1q         trunking      1
Gi0/3       on               802.1q         trunking      1
Gi0/4       on               802.1q         trunking      1
Gi0/5       on               802.1q         trunking      1
Gi0/6       on               802.1q         trunking      1
Gi0/7       on               802.1q         trunking      40
Gi0/8       on               802.1q         trunking      40
Gi0/9       on               802.1q         trunking      40
Gi0/10      on               802.1q         trunking      40

Port        Mode             Encapsulation  Status        Native vlan
Gi0/11      on               802.1q         trunking      40
Gi0/15      on               802.1q         trunking      40
Gi0/16      on               802.1q         trunking      40
Po1         on               802.1q         trunking      1
Po2         on               802.1q         trunking      1

Port        Vlans allowed on trunk
Gi0/1       11-12,14-15,40-46
Gi0/2       11-12,14-15,40-46
Gi0/3       11-12,14-15,40-46
Gi0/4       11-12,14-15,40-46
Gi0/5       11-12,14-15,40-46
Gi0/6       11-12,14-15,40-46
Gi0/7       40
Gi0/8       40
Gi0/9       40
Gi0/10      40
Gi0/11      40
Gi0/15      40
Gi0/16      40
Po1         1,9,11-12,14-15,40-46
Po2         1,9,11-12,14-15,40-46

Port        Vlans allowed and active in management domain
Gi0/1       11-12,14-15,40-46
Gi0/2       11-12,14-15,40-46
Gi0/3       11-12,14-15,40-46
Gi0/4       11-12,14-15,40-46
Gi0/5       11-12,14-15,40-46
Gi0/6       11-12,14-15,40-46
Gi0/7       40
Gi0/8       40
Gi0/9       40
Gi0/10      40
Gi0/11      40
Gi0/15      40
Gi0/16      40
Po1         1,9,11-12,14-15,40-46
Po2         1,9,11-12,14-15,40-46

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/1       11-12,14-15,40-46
Gi0/2       11-12,14-15,40-46
Gi0/3       11-12,14-15,40-46
Gi0/4       11-12,14-15,40-46
Gi0/5       11-12,14-15,40-46
Gi0/6       11-12,14-15,40-46
Gi0/7       40
Gi0/8       40
Gi0/9       40
Gi0/10      40
Gi0/11      40
Gi0/15      40
Gi0/16      40
Po1         1,9,11-12,14-15,40-41
Po2         42-46

SW-BLADE1# sh spanning-tree vlan 41

VLAN0041
  Spanning tree enabled protocol rstp
  Root ID    Priority    4137
             Address     0024.13b5.c080
             Cost        7
             Port        56 (Port-channel1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32809  (priority 32768 sys-id-ext 41)
             Address     0023.05dd.7f80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Desg FWD 4         128.1    P2p Edge
Gi0/2               Desg FWD 4         128.2    P2p Edge
Gi0/3               Desg FWD 4         128.3    P2p Edge
Gi0/4               Desg FWD 4         128.4    P2p Edge
Gi0/5               Desg FWD 4         128.5    P2p Edge
Gi0/6               Desg FWD 4         128.6    P2p Edge
Po1                 Root FWD 3         128.56   P2p
Po2                 Altn BLK 50        128.64   P2p

SW-BLADE1#sh vtp status
VTP Version                     : running VTP2
Configuration Revision          : 10
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 17
VTP Operating Mode              : Client
VTP Domain Name                 : CPR1
VTP Pruning Mode                : Enabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Enabled
MD5 digest                      : 0xC4 0xC1 0x3A 0xA3 0x37 0x93 0x9F 0xD3
Configuration last modified by 10.14.2.3 at 8-13-10 08:21:44
SW-BLADE1#sh vlan id 41

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
41   NLB_exchange                     active    Gi0/1, Gi0/2, Gi0/3, Gi0/4
                                                Gi0/5, Gi0/6, Po1, Po2

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
41   enet  100041     1500  -      -      -        -    -        0      0

Remote SPAN VLAN
----------------
Disabled

Primary Secondary Type              Ports
------- --------- ----------------- ------------------------------------------

Thanks a lot for your help

Tharak Abraham Fri, 08/20/2010 - 06:49

Riziv,

That sounds like an issue with the client1.

Well, the arp response that the router is gonna send after the request from the Client 2 which is connected to the 2950 is a unicast and hence lesser chance for the client 1 to learn the MAC based on that.

What you can do is:-

1. Ping to the Client 2 (on 2950) from Client 1 (on 3020) and see what happens ?

2. If you could sniff on the Client 2 when the Client 1 is doing a Arp request, you may find whether the request is going upstream (since its a broadcast and Client 2 in the same Vlan)

3. Check the MAC address table of the 3020 and see whether the MAC of the gateway is learnt downstream at the trunk.

riziv Fri, 08/20/2010 - 07:52

The client 1 is not the cause of the issue because I have one other client on the blade switch in this

vlan and every client is impacted with the issue.

Ping between client within the vlan is OK.

The mac address of the gateway is well known on the switch 3020.

When the client 2 is connected to the 2960, the arp request is well arriving up to the 3750 router and it reply to the client1

If the client 2 disconnect from the 2960, the client 1 is well doing arp request but does not receive any reponse from the 3750 anymore.

It sound like a bug on C2960 switches.

Switch 2960 already restarted without success.

Regards.

Actions

This Discussion