From: Ovidiu Neghina (o.neghina@gmail.com)
Date: Sat Mar 21 2009 - 13:23:04 ART
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