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bfd and is-is were flapping, because customer change scheduling for CS7 traffic to WFQ

Publication Date:  2013-08-05 Views:  173 Downloads:  0

Issue Description

NE40E has lost connection with NE80E by IS-IS. In logs has message about BFD flapping. Two sites has connected by one ehterchannel contain 5 1G links. After traffic is increase more 80% problem appear.

Handling Process

After checking configuration on interfaces find follow:

interface GigabitEthernet1/0/0

description IOL-P-NE80E-1 gi1/0/0 ##CORE <<IOL_M>>##

undo shutdown

mtu 4470

ip address

isis enable 1

isis circuit-type p2p

isis circuit-level level-2

isis cost 1000

isis ldp-sync

isis bfd enable

isis bfd min-tx-interval 30 min-rx-interval 30


mpls te

mpls rsvp-te

mpls ldp

trust upstream default

port-queue be wfq weight 11 port-wred Default-Core outbound

port-queue af1 wfq weight 57 port-wred Businness-Internet-Core outbound

port-queue af2 wfq weight 4 port-wred Businness-Core outbound

port-queue af3 wfq weight 5 port-wred Critical-Core outbound

port-queue af4 wfq weight 11 outbound

port-queue ef pq shaping shaping-percentage 32 outbound

port-queue cs6 wfq weight 1 outbound    

 port-queue cs7 wfq weight 1 outbound



Root Cause

By defaule such type of traffic has used for protocol needs. In documentation sad that on low-speed links, you can place different service flows into different FQs for WFQ scheduling. Context NOTE: Except CS7 packets, all packets with other CoS values can be configured with WFQ.
So, bfd exchange packets were proceed by wfq querry and after traffic is increase nad up to 80% it start to delay. As result bfd were flapping cause IS-IS flapping.  


Change cs7 type of traffic to default configuration. By default this traffic proceed by FIFO mechanism. And bfd,  IS-IS packets will not be dropped after traffic increased.