ARP request

[vishalpatil86]

HI,

I have core switch connected to 13 other edge switches.

But when i run show arp command, it shows only following switches

coresw#show arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  172.16.10.244         116   0025.4610.9e41  ARPA   Vlan10
Internet  172.16.10.243          38   0024.f98c.0cc1  ARPA   Vlan10
Internet  172.16.10.240         107   0025.4610.3c41  ARPA   Vlan10
Internet  172.16.10.254           0   0015.17ef.43d8  ARPA   Vlan10
Internet  172.16.10.252          43   0024.f761.8041  ARPA   Vlan10
Internet  172.16.10.253           -   001d.7040.8bff  ARPA   Vlan10
Internet  172.16.10.251          47   0025.4610.a0c1  ARPA   Vlan10

why other switches are not showing in this?

[vishalpatil86]

core switch IP is 172.16.10.253

[ranraju · Accepted solution]

So you mean to say the 13 edge switches are connected to this one switch and you want to see their IP addresses in the ARP table.

Ping the switches that you can't see in the ARP table and check if you can see if ARP builds.

Hope this helps..

regards,

ranraju

[vishalpatil86]

ok thanx, its working.

i have one more query.

coresw#show arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  172.16.10.244           9   0025.4610.9e41  ARPA   Vlan10
Internet  172.16.10.243          73   0024.f98c.0cc1  ARPA   Vlan10
Internet  172.16.10.240         142   0025.4610.3c41  ARPA   Vlan10
Internet  172.16.10.241           6   0024.f98c.19c1  ARPA   Vlan10
Internet  172.16.10.254           0   0015.17ef.43d8  ARPA   Vlan10
Internet  172.16.10.252          78   0024.f761.8041  ARPA   Vlan10
Internet  172.16.10.253           -   001d.7040.8bff  ARPA   Vlan10
Internet  172.16.10.251          82   0025.4610.a0c1  ARPA   Vlan10

edge242#show arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  172.16.10.242           -   0024.f91c.0841  ARPA   Vlan10
Internet  172.16.10.254           0   0015.17ef.43d8  ARPA   Vlan10
Internet  172.16.10.252          34   0024.f761.8041  ARPA   Vlan10
Internet  172.16.10.253           3   001d.7040.8bff  ARPA   Vlan10
Internet  172.16.10.250          34   0025.4610.66c1  ARPA   Vlan10

core switch is not showing entry for 172.16.10.242 but edge switch is showing entry for 172.16.10.253

how?

[Latchum Naidu · Accepted solution]

Hi Vishal,

The IP 172.16.10.242 might not connected diretly to the core, it may connected to the core by another switch like through up-link.
The show arp will show you only the direct connected devices, if any device (172.16.10.242) connected through another up-link device then the show arp will show you the up-link device only.

Please click on the correct answer on all posts if they answered your question.
Regards,
Naidu.

[vishalpatil86]

hi,

Wireless controller is directly connected to core switch, and continous communication going on between these two.

den also WLC is not showing in show arp command.

wlc ip is 172.16.10.2

[Latchum Naidu]

Hi Vishal,

Please check the mac address of your wireless controler and try to see that is there in the core switch or not by giving following command.

#show mac-a address aaa.aaa.aaa

By giving the above command it should show the arp entry.

If not shwoing anything by the above command, try to ping once and check.

Please click on the correct answer on all posts if they answered your question.
Regards,
Naidu.

[vishalpatil86]

hi,

i cannot ping wlc either, but it is running fine.

[Latchum Naidu · Accepted solution]

Hi Vishal,

Please try to get the mac address of your wireless controler and try to see the address is there in the core switch by giving following command.

#show mac-a address aaa.aaa.aaa

By giving the above command it should show the arp entry.

Please click on the correct answer on all posts if they answered your question.
Regards,
Naidu.

[vishalpatil86]

hi latchum,

it is showing

coresw#show mac address-table address 88:43:e1:31:19:8b

Unicast Entries
vlan   mac address     type        protocols               port
-------+---------------+--------+---------------------+--------------------
4001    8843.e131.198b   dynamic ip                    GigabitEthernet5/5

But I dont understand thi. Pls explain

[Latchum Naidu]

Hi Vishal,

The output means that your wireless controler is learning from port GigabitEthernet5/5 on your core switch.
And the associated vlan is 4001 (on your core switch)

Now even you can trace your wireless controler physical

Now give command "show ip arp | in aaaa.aaaa.aaaa ---> this will show the associated IP of your wireless controler.

Please click on the correct answer on all posts if they answered your question.
Regards,
Naidu.

[vishalpatil86]

hi,

it is not showing

coresw#show ip arp | in 88:43:e1:31:19:8b

coresw#

and my question is why it is not showing when i run show arp command?

[ranraju]

Do you have connectivity to the ip address that you want to see on the ARP table? I mean can you ping the IP of that device. Only if you are able to ping the device with IP a.b.c.d, you will see a mapping in the ARP table, else you will see the ARP as incomplete. Immidiately after you ping give the command "show ip arp a.b.c.d" or "show ip arp | in a.b.c.d"... and check what happens.

Hope this helps.

regards,

ranraju

[vishalpatil86]

Hi,

i am not able to ping WLC from core switch.

[ranraju]

Arp, Maps an IP address to a MAC address in order to           provide IP communication within a Layer 2 broadcast domain. So inorder for the switch to know the MAC address it has to first be able to reach the device with that IP. If there is no communication, or if the communication is broken then you will not see this IP in the arp-table.

First try to resolve this issue, establish communication between the switch and the WLC - and you would see the arp entry for the WLC on the switch.

Hope this helps.

regards,

ranraju