Good point mate. Will check it out. -----Original Message----- From: Matlock, Kenneth L [mailto:[email protected]] Sent: Thursday, 15 July 2010 9:51 PM To: Aaron Riemer; Phil Mayers Cc: [email protected] Subject: RE: [c-nsp] Brief CPU spikes on 6500 Sup 720
I know it's a longshot, but have you looked at the default gateway on the server? In a pervious job the admin had set the broadcast address (.255) as the gateway, meaning ALL traffic out was getting broadcast. Under normal operation that wasn't a problem, but during backups the flood would occur. Ken Matlock Network Analyst Exempla Healthcare (303) 467-4671 [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Aaron Riemer Sent: Thursday, July 15, 2010 7:45 AM To: 'Phil Mayers' Cc: [email protected] Subject: Re: [c-nsp] Brief CPU spikes on 6500 Sup 720 Guys, We are still seeing these floods. They occur when our backups run and it doesn't matter if the traffic is routed into the vlan or switched within the same vlan as the same problem occurs. Therefore: 1) asymmetric routing cannot be the problem for the L2 switched traffic 2) No TCN's are occurring within the VLAN STP (PVST). 3) Packet captures confirmed that all ports on VLAN1 on one core were receiving the unicast traffic destined for a host on this vlan. 4) From the packet captures we were able to deduce source / dest MAC addresses confirming that the destination MAC was in fact not aging out and could be seen clear as day in the MAC table. Had TAC on the line troubleshooting it for a couple of hours tonight and still no closer to solving the problem. Mac-age time out is set to the same as the arp timeout (4 hours) I don't believe the issue is linked to the CPU spikes but rather the output drops that we are seeing oversubscribing our 6548 line cards. Anyone have any further ideas? Thanks, Aaron. -----Original Message----- From: Phil Mayers [mailto:[email protected]] Sent: Wednesday, 14 July 2010 11:14 PM To: Aaron Riemer Cc: 'Matthew Huff'; 'JC Cockburn'; [email protected] Subject: Re: [c-nsp] Brief CPU spikes on 6500 Sup 720 On 14/07/10 15:51, Aaron Riemer wrote: > Yes i have read all about unicast flooding: > > Can occur by: > > 1) Asymmetric routing > 2) Spanning Tree TCN > 3) MAC aging out > > I cannot see any TCN's or Asymmetric routing so i think we may have to > adjust the mac aging as you suggested. If you're running HSRP, the standby node has a route for the subnet as well as the active e.g. traffic might flow out through the active, and back through the standby as follows: host | active-standby | | (cloud) ^ | | router --/ | target from host->active->router-target return target->router->standby->host ...if "standby" has an ARP entry (default 4 hours) but not MAC table entry (default 5 minutes) it will unknown-unicast-flood the return traffic. If it's a lot of traffic, that will burn a lot of bandwidth... Whether this will happen will depend on your routing topology. > > I am just trying to work out why the hell this has only just started > occurring! Well, without knowing the source of the traffic it's impossible to tell. _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
