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6500 with SLB blade dropped the packets from HA device.

A weird behavior observed in 6500 with SLB blade. the topology is as below:

client--HA---6500 with SLB----server farm

The first Syn packet reached the 6500 with client MAC address as source MAC and can be forwarded to the server correctly. But due to HA vendor special behavior, the second Syn packet's source MAC is rewritten to HA device MAC address and this Syn is dropped by the 6500.

Is this a special feature for 6500? And is it possible to change this behavior?

Thanks in advance.

6 REPLIES
Cisco Employee

Re: 6500 with SLB blade dropped the packets from HA device.

what is the HA device ?

Is it the cat6k that drops the packet or the CSM [slb blade] ?

Capture a trace of the csm etherchannel to verify that the cat6k forwards the packet or not and if the csm drops it or forwards it to the wrong destination.

What version of the CSM soft ?

There is no "feature" to allow packets.

They should go through unless you have sth misconfigured or an old version with possibly a known issue.

Gilles.

New Member

Re: 6500 with SLB blade dropped the packets from HA device.

Thanks for your reply.

1, HA device is from other vendor. It works as transparent mode and the session will be processed by 2 blades in the round-robin schedule.

The first SYN is processed by the master and reach the 6500 with client MAC as the source MAC. the second SYN is processed by the slave and the source MAC is rewritten to the slave's interface mac. This SYN packet is dropped by either 6500 or CSM, not quite sure.

2, The image on the 6500 is as below:

Cisco Internetwork Operating System Software

IOS (tm) s72033_rp Software (s72033_rp-PK9SV-M), Version 12.2(17d)SXB10, RELEASE SOFTWARE (fc1)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2005 by cisco Systems, Inc.

Compiled Thu 11-Aug-05 14:15 by kellythw

Image text-base: 0x40020FBC, data-base: 0x41F20000

cisco WS-C6503-E (R7000) processor (revision 1.1) with 458752K/65536K bytes of memory.

Processor board ID FOX0930005J

SR71000 CPU at 600Mhz, Implementation 0x504, Rev 1.2, 512KB L2 Cache

3, which command should be used to "Capture a trace of the csm etherchannel"?

It seems that only the SYN with rewritten source MAC is dropped. The SYN with client MAC works fine.

Should you need any other information, pls let me know.

Thanks & Regards

Cisco Employee

Re: 6500 with SLB blade dropped the packets from HA device.

the csm drops packets if it does not know the source mac address.

So this is your problem.

You could try to create a static arp entry for the mac address used by your HA device.

Just create a static mac for a non-used ip [does not need to be a real address of your network] and make sure the arp entry is in the vlan of your HA device.

Gilles.

New Member

Re: 6500 with SLB blade dropped the packets from HA device.

Gilles,

Thanks again.

Just check the document and found this command:

"...

Examples This example shows how to configure a static ARP entry:

Router(config-module-csm)# arp 1.1.1.1 0123.4567.89ab vlan 3"

I will encourage the customer to try this command.

Pls correct me if there are something wrong.

Cisco Employee

Re: 6500 with SLB blade dropped the packets from HA device.

that's the correct command.

Let me know how it goes.

Thanks,

Gilles.

New Member

Re: 6500 with SLB blade dropped the packets from HA device.

Gilles,

Thanks.

the customer will try this solution in the near future.

I will update here as soon as I get the feedback.

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