The Cat6509 not generate ARP request

jackson.ku · ‎12-22-2008

Hi,

My Catalyst6509 have one VLAN72, and there are some servers in VLAN72, server A IP address is 10.100.74.5, server B IP address is 10.100.74.30. I tried to ping server A, the server A could reply successfully. But if ping to server B, no replied from server. I used Sniffer to capture all traffics for VLAN72, while ping to server B, the Catalyst 6509 had not generate ARP request packet for server B, so no ARP entry for server B found in Cat6509. I also used another PC in VLAN 72 ( PC C, IP address 10.100.74.100 ), both server A & B can replied ARP and ping packet. Can you give me some advise to resolve this problem?

Best Regards,

Jackson Ku

passioncas · ‎12-22-2008

Hi..

Assign the same IP address(Server B) to another desktop and check it otherwise assign another IP address to the Serevr B and check the reachability.

jackson.ku · ‎12-22-2008

Hi,

I will try it... It is very strange why the Cat6509 have not generate ARP request for server B when I ping from Cat6509 to server B? ( I can make sure no server B's ARP entry in Cat6509 )

Best Regards,

Jackson Ku

jackson.ku · ‎12-22-2008

Hi,

I will try it... It is very strange why the Cat6509 have not generate ARP request for server B when I ping from Cat6509 to server B? ( I can make sure no server B's ARP entry in Cat6509 )

Best Regards,

Jackson Ku

ullasupendran · ‎12-22-2008

Hi jackson

I dont think this is an issue with the cat6509. Check out whether there is a firewall enabled on ur serverB that blocks ICMP reply. Also try to ping from server B to rest of ur network.

Ullas

jackson.ku · ‎12-22-2008

I used Sniffer to capture all traffics for Cat6509 VLAN72, while ping to server B, the Catalyst 6509 had not generate ARP request packet for server B, so no ARP entry for server B found in Cat6509 ...

jackson.ku · ‎12-23-2008

Hi,

I run "debug arp" at core switch, I had not see any ARP request message for server B. Also I see some messages :

Dec 23 16:12:19.972: IP ARP throttled out the ARP Request for 10.100.75.42

Dec 23 16:12:19.972: IP ARP throttled out the ARP Request for 10.100.75.41

Dec 23 16:12:19.972: IP ARP throttled out the ARP Request for 10.100.75.42

Dec 23 16:12:19.976: IP ARP throttled out the ARP Request for 10.100.75.41

Dec 23 16:12:20.400: IP ARP throttled out the ARP Request for 10.100.75.41

Dec 23 16:12:20.400: IP ARP throttled out the ARP Request for 10.100.75.42

Dec 23 16:12:20.404: IP ARP throttled out the ARP Request for 10.100.75.42

Dec 23 16:12:20.404: IP ARP throttled out the ARP Request for 10.100.75.41

Dec 23 16:12:20.724: IP ARP throttled out the ARP Request for 10.100.75.42

Dec 23 16:12:20.724: IP ARP throttled out the ARP Request for 10.100.75.41

Dec 23 16:12:20.724: IP ARP throttled out the ARP Request for 10.100.75.42

Dec 23 16:12:20.724: IP ARP throttled out the ARP Request for 10.100.75.41

The 10.100.75.41 & 10.100.75.42 are old dhcp servers, we have add ip helper-address 10.100.75.41 & ip helper-address 10.100.75.42 at each VLANs. But these 2 DHCP servers no longer use again. I have remove ip helper-address 10.100.75.41 & ip helper-address 10.100.75.42 at each VLANs, but the problem still exist ... What it mean of "IP ARP throttled out" message? Does it cuase this ARP problem?

Best Regards

Jackson Ku

lejoe.thomas · ‎12-23-2008

Hi Jackson,

The above messages appear because CEF cannot locate a valid adjacency for 10.100.75.41 and 10.100.75.42. Hence it punts the packet to the CPU for ARP resolution. Probably some hosts are still using these helper address.

For Cat 6509 not generating ARP requests when pinging server B, it could be because it might already have an entry for Server B's address in the CEF adjacency table.

Verify this with

show adjacency [interface]

show ip arp

http://www.cisco.com/en/US/tech/tk827/tk831/technologies_tech_note09186a0080094303.shtml

HTH

Lejoe

jackson.ku · ‎12-23-2008

Hi,

When problem occur, no entry for Server B's address in both CEF adjacency table and arp table. After I added static ARP entry, it have entry for server B in both CEF adjacency table and arp table. But if I remove static ARP entry, the entry for Server B's address in both CEF adjacency table and arp table disappear immediately.

Best Regard,

Jackson Ku