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CSCso50205 - DNS based SSM mapping creates interface throttles when DNS is not avail


we had problems with SSM multicast with DNS mapping where both DNS servers went down. After a short time one DNS server was up, but the Cisco 7600 routers had to be rebooted because of problems on the interfaces where a simple ICMP was not working but OSPF was fine...

This is probably because of this bug which we found in the release notes for 12.2.SRD.

This is the bug description and I don't understand the last sentence. Do we have to configure this on the DNS server?

Symptoms: If a SSM static mapping command is used and router processes SSM

groups outside the configured static SSM mapping range, routers fall to

DNS-based look to find SSM mapping. If DNS servers are not reachable or DNS

servers are not configured to provide mapping, input interface Q builds up

leading to control plane instabilities affecting other protocols.

Conditions: This symptom occurs when DNS-based SSM mapping and DNS servers

are not reachable.

Workaround: If SSM mapping information is never fetched from a DNS server,


no ip igmp ssm-map query dns.
If DNS is used, ensure that DNS servers are always reachable and also have
low DNS query timeout value.

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