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CPU utilization up to 99 percent caused by ISIS LSP state flush

Publication Date:  2012-07-27 Views:  63 Downloads:  0
Issue Description

In MPLS core netwrok, NE5000E work as P node that just enable ISIS and MPLS LDP protrocol. some packet was dropped by a NE5000E device. this NE5000E have not any response sometimes. the NE5000E verison is VRP (R) software, Version 5.70 (NE5000E V300R007C00SPC500)


Alarm Information

the frist step, CPU status is checked. we find the CPU utilization up to 99%,ROUTRoute task process get 50% and LDP task process get 13%.

the second step, to collect the log information, as below

Dec 29 2011 10:04:26 06_ankara_h2_1 %%01ISIS/6/LDP_ENTER_ACHIEVED(l)[307348]:An interface of the ISIS process 1 entered the ldp-sync-achieved state.

(IfName=Eth-Trunk0)
Dec 29 2011 10:04:26 06_ankara_h2_1 %%01ISIS/6/RCV_ERR_LSP(l)[307349]:ISIS 1 received an incorrect LSP packet on the interface from SNPA. (Reason=UPDT:

Extended Nbr metric excced MAX_LINK_METRIC., InterfaceName=Eth-Trunk0, SnpaAddress=0025.ba72.61c4, NeighborSystemId=0000.0000.0000, LspId=XXXX.XXXX.XXX3.00-

00, LspSequenceNumber=0x1be5, PduType=20, TlvType=22, Offset=50)
Dec 29 2011 10:04:26 06_ankara_h2_1 %%01ISIS/6/RCV_ERR_LSP(l)[307350]:ISIS 1 received an incorrect LSP packet on the interface from SNPA. (Reason=UPDT:

Extended Nbr metric excced MAX_LINK_METRIC., InterfaceName=GE1/0/9, SnpaAddress=286e.d406.c4d7, NeighborSystemId=0000.0000.0000, LspId=XXXX.XXXX.XXX3.00-00,

LspSequenceNumber=0x1be5, PduType=20, TlvType=22, Offset=50)
Dec 29 2011 10:04:26 06_ankara_h2_1 %%01ISIS/6/RCV_ERR_LSP(l)[307351]:ISIS 1 received an incorrect LSP packet on the interface from SNPA. (Reason=UPDT:

Extended Nbr metric excced MAX_LINK_METRIC., InterfaceName=GE1/0/8, SnpaAddress=286e.d406.c53c, NeighborSystemId=0000.0000.0000, LspId=XXXX.XXXX.XXX3.00-00,

LspSequenceNumber=0x1be5, PduType=20, TlvType=22, Offset=50)
Dec 29 2011 10:04:34 06_ankara_h2_1 %%01ISIS/6/RCV_ERR_LSP(l)[307352]:ISIS 1 received an incorrect LSP packet on the interface from SNPA. (Reason=UPDT:

Extended Nbr metric excced MAX_LINK_METRIC., InterfaceName=Eth-Trunk0, SnpaAddress=0025.ba72.61c4, NeighborSystemId=0000.0000.0000, LspId=XXXX.XXXX.XXX3.00-

00, LspSequenceNumber=0x1be6, PduType=20, TlvType=22, Offset=50)
Dec 29 2011 10:04:34 06_ankara_h2_1 %%01RM/4/IPV4_DEFT_RT_CHG(l)[307353]:IPV4 default Route is changed.

(ChangeType=Delete,InstanceId=0,Protocol=ISIS,ExitIf=Eth-Trunk0,Nexthop=XXX.XXX.XXX.9,Neighbour=0.0.0.0,Preference=18,Label=4294967295,Metric=16777253)


Dec 29 2011 10:05:01 06_ankara_h2_1 %%01LDP/4/SSNHOLDTMREXP(l)[307360]:Sessions were deleted because the session hold timer expired and the notification of

the expiry was sent to the peer XXX.XXX.XXX.21.
Dec 29 2011 10:05:01 06_ankara_h2_1 %%01ISIS/6/LDP_ENTER_HMC(l)[307361]:An interface of the ISIS process 1 entered the ldp-sync-holdMaxCost state.

(IfName=Eth-Trunk0)


Handling Process
we change to isis cost 16777214, to verify it again. the problem is sloved.
Root Cause

About CPU 99% utilization, it is caused by ISIS lsp state flush.Our ISIS process receive LSP with max metric from XXXX.XXXX.XXX3 , XXXX.XXXX.XXX2, XXXX.XXXX.XXX3.
From log : Reason=UPDT: Extended Nbr metric excced MAX_LINK_METRIC.

and then check configuration, we find like as:

interface Eth-Trunk0
mtu 9212
ip address X.X.X.X 255.255.255.252
isis enable 1
isis circuit-type p2p
isis circuit-level level-2
isis cost 16777215

If the cost is 16777215, the Neighbor TLV (cost is 16777215) generated on the link cannot be used for route calculation and can be used only to deliver the

information related to LDP/TE. The maximum cost of the received route is 0x FFFFFFFF.

LDP session can setup initially, but route module notified ISIS of the status UNREACHABLE(maximum cost) of the LDP session, LDP session will down soon. And

then ldp session setup again so circulates.


Suggestions

In RFC3784 description:“If a link is advertised with the maximum link metric (2^24 - 1), this link MUST NOT be considered during the normal SPF

computation. ”2^24 - 1 equal to 16777215.

so suggest that our isis metric command line have include two parts,1~16777214 and maximum, like cisco CLI.


END