We have two DC's with 10G interconnection in between - these connections are run as L2 links - put into a set of nexus 5000 (the old nx5020) - acting access-switches - and uplinked to a set of nexus 7009 which act as L3 switch for us.
We have a cluster of vmware boxes in each site and are running MS windows 2008 machines with MS NLB for TerminalServices - in IGMP multicast mode - in VLAN 21.
Now I looked in the log of the nexus 7000 and found that the PIM DR is "flapping" between the two sites from time to time:
2013 Nov 25 22:50:58 ve-coresw-01 %PIM-5-DR_CHANGE: pim  DR change from 172.21.159.253 to 172.21.144.3 on interface Vlan21
2013 Nov 25 22:51:54 ve-coresw-01 %PIM-5-DR_CHANGE: pim  DR change from 172.21.144.3 to 172.21.159.253 on interface Vlan21
2013 Nov 25 23:26:07 ve-coresw-01 %PIM-5-DR_CHANGE: pim  DR change from 172.21.159.253 to 172.21.144.3 on interface Vlan21
2013 Nov 25 23:26:10 ve-coresw-01 %PIM-5-DR_CHANGE: pim  DR change from 172.21.144.3 to 172.21.159.253 on interface Vlan21
I am not that familiar with multicast but the basic concepts are there - in the vrf I have defined
ip pim ssm range 184.108.40.206/8
the vlan is defined as:
vlan configuration 21
layer-2 multicast lookup mac
under the SVI interface vlan 21 I have also defined - and there is a sample showning the nlb
vrf member DMZ_21
no ip redirects
ip address 172.21.144.3/20
ip pim sparse-mode
ip arp 172.21.149.19 0100.5E7F.9513
these flapping should only occur if the keep-alives between the two sites are missed 3 times
The uplinks to the nexus 5000 are defined as mrouters
ip igmp snooping mrouter interface port-channel5
ip igmp snooping mrouter interface port-channel16
SW5020-01# sh ip igmp snooping vl 21
IGMP Snooping information for vlan 21
IGMP snooping enabled
IGMP querier present, address: 172.21.144.3, version: 2, interface port-channel5 -> the DR on the nx7k
IGMPv3 Explicit tracking enabled
IGMPv2 Fast leave disabled
IGMPv1/v2 Report suppression enabled
IGMPv3 Report suppression disabled
Link Local Groups suppression enabled
Router port detection using PIM Hellos, IGMP Queries
Number of router-ports: 3
Number of groups: 3
VLAN vPC function enabled
Po10 Po15 Eth1/3 Eth1/11
Eth1/12 Eth1/13 Eth1/14 Eth1/15
Eth1/16 Eth1/17 Eth1/18 Eth1/19
Eth1/20 Eth1/25 Eth1/26 Eth1/27
Eth1/28 Eth1/29 Eth1/30 Eth1/31
Eth1/32 Po16 Po5
The link between the two sites - and boxes - is running error-free. As far as I can see there hasn't been any problems in that vlan since ??
If I look at f.ex spanning-tree the topology hast changed for long time in that vlan (2 weeks).
Could I harden the igmp multicast setup?
What is happening when a DR is changing? Will the multicast stop work or what happens?
As far as I understood the DR is the service which forwards the multicast traffic to the groups so if suddenly some re-negotiation occurs I would expect that the active traffic will be interrupted.
here the actual MS NLB clusters adresses:
SW5020-01# sh ip igmp snooping groups vl 21 Type: S - Static, D - Dynamic, R - Router port
Vlan Group Address Ver Type Port list 21 */* - R Po10 Po16 Po5 21 220.127.116.11 v1 D Eth1/14 Eth1/19 Eth1/32 21 18.104.22.168 v1 D Eth1/12 Eth1/15 Eth1/16 Eth1/26 Eth1/31 21 22.214.171.124 v2 D Po15 Eth1/11 Eth1/28 Eth1/29 SW5020-01#
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