How to use secondary path on WAN during media Fluctation on 7600 Router in OSPF environment

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Jan 26th, 2010
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We are using redundant Pont to Point STM / DS3 over the wan for connecting with other remote locations, Load sharing and redundancy is happening perfectly with OSPF, but if media Fluctatues then packet srart drops and connectivity goes down. Please tell how to resolve this issue.



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spremkumar Wed, 01/27/2010 - 02:30
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Hi Prince

I am afraid if you can do something for this, since the problem is with the physical link you tend to see packet drops when you are doing load sharing with multiple physical links. Better way to overcome is to do proper testing of both the physical links before accepting the same from your telco.

Normally you do a 48Hrs error testing before you accept the link and pass on the live traffic onto it.


prince.mtsindia Wed, 01/27/2010 - 04:06
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Hi Kumar

Thanks for your reply...

Can I use "IP SLA" or any other machnisim, which count errors on particular link and if errors crossed a certain limit then traffic should shift  on Other stable link without disconnection in SCTP packets.



Giuseppe Larosa Wed, 01/27/2010 - 05:12
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Hello Prince,

if all devices are C7600 you can think to use BFD to perform IP fast convergence:

if the issue is errors from time to time it can help to skip using the affected link


feature navigator says:

C7600 sup720/MSFC3

you can use an IOS 12.2(33) SRD3 or SRE

search by feature type BFD OSPF Support for BFD over IPv4

Hope to help


prince.mtsindia Sun, 01/31/2010 - 07:17
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Hello Giuslar,

Thanks for your valuable inputs.

I have gone through  below the mentioned link on BFD, Please clarify my few queries on the same.

As I mentioned earlier, we are carrying SCTP (Signaling) traffic on P2P links DS3 & -Multilinks (Channelized Optical E1's) on the WAN with OSPF. During the Fluctuation, we got input and output errors on link. Find below the link detail. but link does'nt go down, OSPF failover mechnism works only when the active link goes down.

Is BFD can help to shift the traffic from fluctuated link to another suitable link?

WAN-RTR-CHN-7606-001#sh int Serial2/0/0.1/2

Serial2/0/0.1/2 is up, line protocol is up

  Hardware is SPA-1XCHSTM1/OC3

  Description: ***Railtel_DS3_CHN_BANGA_PDSN***

  Internet address is

  MTU 4470 bytes, BW 44210 Kbit, DLY 200 usec,

     reliability 255/255, txload 101/255, rxload 37/255

  Encapsulation PPP, LCP Open, multilink Closed

  Open: IPCP, CDPCP, crc 16, loopback not set

  Keepalive set (10 sec)

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

  Last clearing of "show interface" counters 2w5d

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 4627

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 6467000 bits/sec, 2616 packets/sec

  5 minute output rate 17553000 bits/sec, 4407 packets/sec

     2650934928 packets input, 618880707937 bytes, 0 no buffer

     Received 0 broadcasts (0 IP multicasts)

     0 runts, 0 giants, 0 throttles

              0 parity

     159357 input errors, 21527 CRC, 31479 frame, 0 overrun, 0 ignored, 106351 abort

     3626753481 packets output, 2327272737770 bytes, 0 underruns

     7892 output errors, 0 applique, 11 interface resets

     0 output buffer failures, 0 output buffers swapped out

     11 carrier transitions no alarm present

  DSU mode cisco, bandwidth 44210 Kbit, scramble 0, VC 21, non-inverted data

interface Serial2/0/0.1/2
description ***Railtel_DS3_CHN_BANGA_PDSN***
ip address
no ip proxy-arp
encapsulation ppp
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 7 071F33435A060A0014
ip ospf network point-to-point
ppp multilink
ppp multilink group 450
dsu bandwidth 44210
framing c-bit
cablelength 10


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