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New Member

LDP session flap on a 7600 router

Hi guys,,

Please refer below the brief intro to the problem:

LDP neighbor went down [as seen in the below logs] for around few secs between below mentioned PE device to the two uplinks P devices.

Please refer to the note detail Topology:

PE[tE x/0/0] -------- TE Tunnel ------ P Device @ A location

    [Te y/0/0] ------ TE Tunnel-------- P Device @ B location

#Show logs

917597: Mar  8 08:10:09 SAST: %LDP-5-NBRCHG: LDP Neighbor a.b.c.d:0 (5) is DOWN (TCP

connection closed by peer)

917664: Mar  8 08:10:19 SAST: %LDP-5-NBRCHG: LDP Neighbor e.f.g.h:0 (1) is DOWN

(Session KeepAlive Timer expired)

917701: Mar  8 08:10:21 SAST: %LDP-5-NBRCHG: LDP Neighbor a.b.c.d:0 (5) is UP

917771: Mar  8 08:10:23 SAST: %LDP-5-NBRCHG: LDP Neighbor e.f.g.h:0 (7) is UP

Please anybody can tell what was the reason behind the LDP flap?

Regards

Pradip

  • MPLS
Everyone's tags (3)
11 REPLIES
New Member

LDP session flap on a 7600 router

your problem is keepalive timer expired, not the hello timer expired, you need to firstly check the timer you had already configured,

The command

show mpls ldp parameters

can be used to review the locally configured timers and the command

show mpls ldp neighbor details can be used to show the final negotiated timers

The command

show mpls ldp parameters can be used to review the locally configured timers and the command

show mpls ldp neighbor details can be used to show the final negotiated timers

if the timer is 180s, i think it is a long time, you need to check the circuit problem, it is not the configuration problem.

New Member

LDP session flap on a 7600 router

Hi Hu xu,

Thank you for reply..

Please find the output of the ldp parameter:

#show mpls ldp parameters

Protocol version: 1

Session hold time: 180 sec; keep alive interval: 60 sec

Discovery hello: holdtime: 15 sec; interval: 5 sec

Discovery targeted hello: holdtime: 90 sec; interval: 10 sec

Downstream on Demand max hop count: 255

LDP for targeted sessions

LDP initial/maximum backoff: 15/120 sec

LDP loop detection: off

timer seems to be 180sec.

There was no any physical problem as all other protocol i.e ISIS(IGP) was stable on same link at the time of problem. We observed flap in a LDP protocol only.

Regards

Pradip

New Member

LDP session flap on a 7600 router

Anyone has any clue please ??

Cheers

Pradip

Cisco Employee

LDP session flap on a 7600 router

Hello Pradeep

Can you please check the following:

- show ibc

- show interface (output of the connected interfaces on both the routers.)

Has the targetted ldp flapped or the ldp on the physical interface

Since this was a TCP connection closed. You can also check for the TCP MSS value. it may be possible due to some reason it might have got negotiated with lower value and have caused the LDP to flap.

Please provide the above information. I can look further into this.

Regards

Vinit

Thanks
--VJ
New Member

LDP session flap on a 7600 router

Hi Vinit,

Please find below the o/p of both show ibc & show int:

# show ibc

Interface information:

        Interface IBC0/0(idb 0x1D224BF0)

        5 minute rx rate 390000 bits/sec, 470 packets/sec

        5 minute tx rate 724000 bits/sec, 696 packets/sec

        1227785718 packets input, 132277835813 bytes

        531848764 broadcasts received

        703054986 packets output, 89510912001 bytes

        53000709 broadcasts sent

        0 Bridge Packet loopback drops

        386955797 Packets CEF Switched, 58076 Packets Fast Switched

        0 Packets SLB Switched, 0 Packets CWAN Switched

        Label switched pkts dropped: 0    Pkts dropped during dma: 219471401

        Invalid pkts dropped: 57811    Pkts dropped(not cwan consumed): 8925

        Xconnect pkts processed: 0, dropped: 1111508

        Xconnect pkt reflection drops: 0

        Total paks copied for process level 0

        Total short paks sent in route cache 78654011

        Total throttle drops 218301133    Input queue drops 773327

        total spd packets classified (456244739 low, 359912505 medium, 20316995 high)

        total spd packets dropped (153503515 low, 65948095 medium, 41 high)

        spd prio pkts allowed in due to selective throttling (0 med, 0 high)

        IBC resets   = 1; last at 05:12:26.831 SAST Wed Feb 8 2012

Driver Level Counters: (Cumulative, Zeroed only at Reset)

          Frames          Bytes

  Rx(0)   368004372       1762711303

  Rx(1)   913412478       2159603712

  Tx(0)   728948380       3037780905

Input Drop Frame Count

     Rx0 = 22141            Rx1 = 996745

Per Queue Receive Errors:

     FRME   OFLW   BUFE   NOENP  DISCRD DISABLE BADCOUNT

Rx0 0      0      0      0      0        0    0

Rx1 0      0      0      68     0        0    0

  Tx Errors/State:

   One Collision Error   = 0            More Collisions       = 0

   No Encap Error        = 0            Deferred Error        = 0

   Loss Carrier Error    = 0            Late Collision Error  = 0

   Excessive Collisions  = 0            Buffer Error          = 0

   Tx Freeze Count       = 0            Tx Intrpt Serv timeout= 1

  Counters collected at Idb:

   Is input throttled    = 0            Throttle Count        = 0

   Rx Resource Errors    = 0            Input Drops           = 1104309

   Input Errors           = 610494

   Output Drops          = 0            Giants/Runts          = 0/0

   Dma Mem Error         = 0            Input Overrun         = 0

#show int te X/0/0

TenGigabitEthernetX/0/0 is up, line protocol is up (connected)

  MTU 4470 bytes, BW 10000000 Kbit, DLY 10 usec,

     reliability 255/255, txload 20/255, rxload 43/255

  Encapsulation ARPA, loopback not set

  Keepalive not supported

  Carrier delay is 0 msec

  Full-duplex, 10Gb/s

  Transport mode LAN (10GBASE-R, 10.3125Gb/s)

  input flow-control is on, output flow-control is on

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters 2w1d

  Input queue: 0/75/38/33 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: Class-based queueing

  Output queue: 0/40 (size/max)

  5 minute input rate 1691089000 bits/sec, 390075 packets/sec

  5 minute output rate 818470000 bits/sec, 413745 packets/sec

  L2 Switched: ucast: 5460795 pkt, 851382131 bytes - mcast: 557617 pkt, 63052504 bytes

  L3 in Switched: ucast: 72659051788 pkt, 57114890177182 bytes - mcast: 0 pkt, 0 bytes mcast

  L3 out Switched: ucast: 237095519242 pkt, 42944537492139 bytes mcast: 0 pkt, 0 bytes

     704163207990 packets input, 315321595661874 bytes, 1 no buffer

     Received 1125 broadcasts (0 IP multicasts)

     0 runts, 0 giants, 3 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 567310 multicast, 0 pause input

     0 input packets with dribble condition detected

     786519825664 packets output, 210404496698710 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 pause output

     0 output buffer failures, 0 output buffers swapped out

#show int te X/0/0

TenGigabitEthernetY/0/0 is up, line protocol is up (connected)

  MTU 4470 bytes, BW 10000000 Kbit, DLY 10 usec,

     reliability 255/255, txload 5/255, rxload 2/255

  Encapsulation ARPA, loopback not set

  Keepalive not supported

  Carrier delay is 0 msec

  Full-duplex, 10Gb/s

  Transport mode LAN (10GBASE-R, 10.3125Gb/s)

  input flow-control is on, output flow-control is on

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters 2w1d

  Input queue: 0/75/292/19 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: Class-based queueing

  Output queue: 0/40 (size/max)

  5 minute input rate 112466000 bits/sec, 66131 packets/sec

  5 minute output rate 221669000 bits/sec, 69520 packets/sec

  L2 Switched: ucast: 2161150 pkt, 440372316 bytes - mcast: 514981 pkt, 65137030 bytes

  L3 in Switched: ucast: 5460878448 pkt, 1060741666543 bytes - mcast: 0 pkt, 0 bytes mcast

  L3 out Switched: ucast: 3518851937 pkt, 2138635500086 bytes mcast: 0 pkt, 0 bytes

     136383893748 packets input, 34454049909804 bytes, 1 no buffer

     Received 1125 broadcasts (0 IP multicasts)

     0 runts, 0 giants, 3 throttles

     267 input errors, 220 CRC, 47 frame, 0 overrun, 0 ignored

     0 watchdog, 536405 multicast, 0 pause input

     0 input packets with dribble condition detected

     124870339660 packets output, 57889219631351 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 pause output

     0 output buffer failures, 0 output buffers swapped out

There was no any flap observed on the physical interface. IGP protocol is also running thru the same physical links & that was UP & stable.

Please tell me how do we check the TCP MSS value this LDP sessions.

- Pradip

Cisco Employee

LDP session flap on a 7600 router

Hello Pradip

I noticed a couple of things in the above logs:

1. In the show ibc output, i noticed that there are input queue driops, this means that there are packets that have been dropped by the RP of the router.

2. on the first TenGig interface, i see input queue drops and on the other one, I notice a huge number of input queue drops which means that the interface has run out of buffer and has started dropping the packets. This may sometimes lead to control plane packets getting dropped. For this I will recommend you to increase the hold queue size on the interface using the interface command : "hold-queue 2000 in". This will increase the input hold queue size.

3. I also notice input errors, CRC errors on the 2nd TenGig interface. This basically points to some issue on the interface of the media on that link. Can you please get the fiber checked along with the sfp.

3. I will also recommend you to configure mpls ldp sync.

Regards

Vinit

Thanks
--VJ
New Member

LDP session flap on a 7600 router

Thanks vinit,

Point#2: Increasing the hold-queue will impact the any operation of the network including voice traffic.

Point#3: May I know the purpose of that command please ?

-Regards

Pradip

Cisco Employee

LDP session flap on a 7600 router

Hello Pradip

Point2# No, increasing the hold queue will not have any impact on the network operation.

Point3# There are many benefits of this command. You may want to refer to the below link. This will answer your question.

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/fsldpsyn.html#wp1053817

Regards

Vinit

Thanks
--VJ
New Member

LDP session flap on a 7600 router

Thnk you for prompt reply

-Pradip

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