From: Ovidiu Neghina (o.neghina@gmail.com)
Date: Sat Mar 21 2009 - 18:52:06 ART
forget it.....it forgot the basics of switch...we can't have two
identical MACs on the same vlan....
On Sat, Mar 21, 2009 at 6:23 PM, Ovidiu Neghina <o.neghina@gmail.com> wrote:
> I have read and did several labs with VRRP. I understand the concept
> and details (virtual ip , virtual mac) but I have one question : when
> we switchover from a master to a backup why is the virtual mac address
> of the old master disappearing from the mac-address table of the
> switch so fast ? I was expecting to have it at least 300 seconds(the
> aging timer of CAM switch).
> I know that when a router becomes Master it sends gratuitous ARP
> requests with the virtual ip and virtual mac so the switch updates
> his CAM table but I was expecting, after switchover, to see on the
> switch the virtual mac address both on the interface toward the new
> master and old master ....at least 300 seconds - the aging timer of
> CAM.
>
> Lets say we have this example :
> |------------R5 (Backup)
> |
> R6---|
> |
> |------------R4 (Master) ---- serial tracked
>
> R6, R4, R5 are connected to a 3550 switch in vlan 456.
>
> 0000.5e00.0101 is the virtual mac address of the group
> Normal operation: R4 master, R5 backup; switch has the following
> mac-address table:
>
> Rack1R7#sh mac-address-table vlan 456
> Destination Address Address Type VLAN Destination Port
> ------------------- ------------ ---- --------------------
> cc05.1200.0000 Dynamic 456 FastEthernet1/6
> cc04.1200.0000 Dynamic 456 FastEthernet1/5
> cc03.1200.0000 Dynamic 456 FastEthernet1/4
> 0000.5e00.0101 Dynamic 456 FastEthernet1/4
> <<<<<<<this is the interface toward R4 on the switch
>
> Rack1R7#
> We switchover from R4 to R5 (we track on R4 the serial interface and
> decrement priority on R4 when the interface is down) and instantly on
> the switch we have :
> Rack1R7#sh mac-address-table vlan 456
> Destination Address Address Type VLAN Destination Port
> ------------------- ------------ ---- --------------------
> cc05.1200.0000 Dynamic 456 FastEthernet1/6
> cc04.1200.0000 Dynamic 456 FastEthernet1/5
> cc03.1200.0000 Dynamic 456 FastEthernet1/4
> 0000.5e00.0101 Dynamic 456
> FastEthernet1/5<<<<<<<<<this is the interaface toward R5
>
> Rack1R7#
> As you can see we do not have the virtual mac address on FastEthernet
> 1/4 anymore , I was expecting to have it for 300 seconds (aging time
> on the switch)
> I see that 2 kinds of gratuitous arp are sent by the new Master R5
> Rack1R5#
> IP ARP: sent rep src 155.1.100.254 0000.5e00.0101,
> dst 155.1.100.254 ffff.ffff.ffff Ethernet0/0
>
> IP ARP: sent rep src 155.1.100.254 0000.5e00.0101,
> dst 155.1.100.254 0100.0ccd.cdcd Ethernet0/0
> <<<<<<<<<<< I am quessing this packet sent to , 0100.0ccd.cdcd ,
> STP-UplinkFast mac address makes the switch to flush the mac address
> table and relearn all mac addresses.
>
> What do you think ? Any feedback is appreciated.
>
> Ovidiu
Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Mon Apr 06 2009 - 06:44:06 ART