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New Member

Unequal serial link cost in Point to point OSPF Link

Hi all,

le

I have question regarding OSPF point to point serial link cost   ---

I have 2 Routers conencted back to back with T1 cross over cable.

Router 1

2650XM#      sh run int se0/0
Building configuration...

Current configuration : 165 bytes
!
interface Serial0/0
ip address 10.20.4.1 255.255.255.0
ip ospf hello-interval 40
service-module t1 clock source internal
service-module t1 timeslots 1-24
end

2650XM#sh ip ospf int se0/0
Serial0/0 is up, line protocol is up
  Internet Address 10.20.4.1/24, Area 3
  Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 65 ***************************************************
  Transmit Delay is 1 sec, State POINT_TO_POINT,
  Timer intervals configured, Hello 40, Dead 160, Wait 160, Retransmit 5
    oob-resync timeout 160
    Hello due in 00:00:17
  Index 1/6, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 5.5.5.5
  Suppress hello for 0 neighbor(s)

*******************************************************************************************

Router 2

Serial0/0 is up, line protocol is up
  Internet Address 10.20.4.2/24, Area 3
  Process ID 1, Router ID 5.5.5.5, Network Type POINT_TO_POINT, Cost: 64 *******************************************
  Transmit Delay is 1 sec, State POINT_TO_POINT,
  Timer intervals configured, Hello 40, Dead 160, Wait 160, Retransmit 5
    oob-resync timeout 160
    Hello due in 00:00:34
  Index 1/6, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 1.1.1.1
  Suppress hello for 0 neighbor(s)


2620Router# sh run int se0/0
Building configuration...

Current configuration : 90 bytes
!
interface Serial0/0
ip address 10.20.4.2 255.255.255.0
ip ospf hello-interval 40
end

My question is why i serial link shows cost as  64 and other as 65?

Is this normal  in serial link of OSPF ?

Thanks

MAhesh

1 ACCEPTED SOLUTION

Accepted Solutions
VIP Super Bronze

Unequal serial link cost in Point to point OSPF Link

Mahesh,

The issue was the bandwidth.  According to the calculation I provided above, it should be 64.76, but as along as they are both the same then this should not be an issue. So you are good to go.....

HTH

9 REPLIES
Purple

Unequal serial link cost in Point to point OSPF Link

Hi,

It should be the same on both unless you modified the bandwidth or the reference bandwidth on R1.

Could you post sh int s0/0  as well as sh run | section ospf on R1

Regards.

Alain

Don't forget to rate helpful posts.
New Member

Unequal serial link cost in Point to point OSPF Link

Hi Cadet,

Thanks for reply.

Here is info from R1

2650XM#sh int serial 0/0
Serial0/0 is up, line protocol is up
  Hardware is PQUICC with Fractional T1 CSU/DSU
  Internet address is 10.20.4.1/24
  MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec,***************************
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:07, output hang never
  Last clearing of "show interface" counters 1d03h
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops)
     Conversations  0/1/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1152 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     11687 packets input, 814409 bytes, 0 no buffer
     Received 11347 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     11639 packets output, 831642 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

2650XM#sh run | inc  section ospf on R1
2650XM#

R2 Router

2620Router#sh int se0/0

Serial0/0 is up, line protocol is up

  Hardware is PQUICC with Fractional T1 CSU/DSU

  Internet address is 10.20.4.2/24

  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,*******************************************

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation HDLC, loopback not set

  Keepalive set (10 sec)

  Last input 00:00:08, output 00:00:02, output hang never

  Last clearing of "show interface" counters 1d03h

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

  Queueing strategy: weighted fair

  Output queue: 0/1000/64/0 (size/max total/threshold/drops)

     Conversations  0/1/256 (active/max active/max total)

     Reserved Conversations 0/0 (allocated/max allocated)

     Available Bandwidth 1158 kilobits/sec

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 0 bits/sec, 0 packets/sec

     11675 packets input, 834456 bytes, 0 no buffer

     Received 11377 broadcasts, 0 runts, 0 giants, 0 throttles

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

     11721 packets output, 816733 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 output buffer failures, 0 output buffers swapped out

     0 carrier transitions

     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

I see bandwidth is different on both links.

Is thats the cause of issue?

Thanks

MAhesh

VIP Super Bronze

Unequal serial link cost in Point to point OSPF Link

Mahesh,

Yes, that is the problem. can you change

service-module t1 timeslots 1-24 to

service-module t1 timeslots 1-24 speed 64

and try again?

HTH

Reza

New Member

Unequal serial link cost in Point to point OSPF Link

Hi Reza,

I did that on R1 router and then did unplug the cable.

Still same thing as below

  Suppress hello for 0 neighbor(s)

2650XM# sh int se0/0

Serial0/0 is up, line protocol is up

  Hardware is PQUICC with Fractional T1 CSU/DSU

  Internet address is 10.20.4.1/24

  MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec,

     reliability 255/255, txload 1/255, rxload 1/255

Serial0/0 is up, line protocol is up

  Internet Address 10.20.4.1/24, Area 3

  Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 65

  Transmit Delay is 1 sec, State POINT_TO_POINT,

  Timer intervals configured, Hello 40, Dead 160, Wait 160, Retransmit 5

    oob-resync timeout 160

    Hello due in 00:00:33

  Index 1/6, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 1

  Last flood scan time is 0 msec, maximum is 4 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 5.5.5.5

  Suppress hello for 0 neighbor(s)

2650XM#

  Suppress hello for 0 neighbor(s)

Serial0/0 is up, line protocol is up
  Internet Address 10.20.4.1/24, Area 3
  Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 65
  Transmit Delay is 1 sec, State POINT_TO_POINT,
  Timer intervals configured, Hello 40, Dead 160, Wait 160, Retransmit 5
    oob-resync timeout 160
    Hello due in 00:00:33
  Index 1/6, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 5.5.5.5
  Suppress hello for 0 neighbor(s)
2650XM#

Thanks

MAhesh

VIP Super Bronze

Re: Unequal serial link cost in Point to point OSPF Link

Ok, can you add these 2 commands to r1 (dce side) and try again?

service-module t1 framing esf
service-module t1 linecode b8zs

HTH

New Member

Unequal serial link cost in Point to point OSPF Link

Hi Reza,

I added the command ---service-module t1 timeslots 1-24 speed 64

on R2  router and now cost is 65 on both links

2620Router#sh int se0/0

Serial0/0 is up, line protocol is up

  Hardware is PQUICC with Fractional T1 CSU/DSU

  Internet address is 10.20.4.2/24

  MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec,

Serial0/0 is up, line protocol is up

  Internet Address 10.20.4.2/24, Area 3

  Process ID 1, Router ID 5.5.5.5, Network Type POINT_TO_POINT, Cost: 65

  Transmit Delay is 1 sec, State POINT_TO_POINT,

  Timer intervals configured, Hello 40, Dead 160, Wait 160, Retransmit 5

    oob-resync timeout 160

    Hello due in 00:00:37

  Index 1/6, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 1

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 1.1.1.1

  Suppress hello for 0 neighbor(s)

2620Router#

So now bandwidth is same on both links.

And both shows cost of 65 is that normal?

So issue was with bandwidth difference between two links right??

Thanks

Mahesh

VIP Super Bronze

Unequal serial link cost in Point to point OSPF Link

Mahesh,

The issue was the bandwidth.  According to the calculation I provided above, it should be 64.76, but as along as they are both the same then this should not be an issue. So you are good to go.....

HTH

New Member

Unequal serial link cost in Point to point OSPF Link

Many thanks again Reza.

Mahesh

VIP Super Bronze

Unequal serial link cost in Point to point OSPF Link

Hi Mahesh,

Both sides should be 64.

cost= 10000 0000/bandwith in bps

So, in you case sine it is a full T1, we take 100,000 and divided it by 1544

100000/1544=64

Can you sh and no sh the interface on r1?

if this does not help,  can you disconnect the cable and reconnect it?

HTH

Reza

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