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why lose packets between two 7507 routers ?

li-he
Level 1
Level 1

Dear all :

I just have a problem that I can not explain the reason:

PC--cat6500(gw)---Rt1_7507(atm)---(atm)Rt2_7507.The two routers are connected by ATM line (each router hase a PA-A3-OC3SMI). On Rt1_7507 ,I ping the Rt2_7507's directly connected port address(extend ping ) ,and I find about 2% packets lost during ping .The packet size is 18024 .But when I ping Rt2_7507's wan interface on PC with same packet size ,no packet is lost .

the IOS version of two router is 12.1.19e6 . why ?

5 Replies 5

vmoopeung
Level 5
Level 5

Typically when you test packet loss with ping don't ping the router itself because it consider the processing of ICMP echo reply a low task and if the box is loaded it will simply discard them. However try to ping a device that is beyond the router. This is a more reliable test.

but,the router is light load (almost no load ) and the bandwidth of the wan link is 10M .So I think there lies in othe reason .

smif101
Level 4
Level 4

What type of ATM circuit do you have, what is the exact bandwidth the ISP is providing and what is your config state. I would first decrease the bandwidth alloted in your routers to 9Mbs and see if that fixes your problem. You might just be over the limit a little which will cause problems. Let me know if that works and please provide your configs on both sides.

Jason Smith

www.smif101.com

Steve Fuller
Level 9
Level 9

The big difference between the ping from the PC and the router is the size of the packet. When you ping from the PC it will be a 1500-byte packet, which is around 32 ATM cells. When you ping from the router you've said it's an 18,024-byte packet which is around 376 cells.

If you over-subscribe the service that the carrier has provided they will drop cells. One dropped cell is a lost ping.

The chances of cell loss for the large packet is much greater.

Drop the ping size on the router and see if you loose any packets. Also check the output of the "sh int" and look to see if you're getting any CRCs. On ATM these are typically caused by dropped cells within the service provider.

Regards

If you do a sh atm pvc vpi/vci look for CRC error in this command , this indicates you are exceeding your contracted rate . Watch for it incrementing while pinging. If you ping and drop while below the size of your PVC then the provider has something misconfigured.

sh atm pvc vpi/vci

VBR-NRT, PeakRate: 2000, Average Rate: 2000, Burst Cells: 32

AAL5-LLC/SNAP, etype:0x0, Flags: 0x20, VCmode: 0x0

OAM frequency: 0 second(s), OAM retry frequency: 1 second(s), OAM retry frequency: 1 second(s)

OAM up retry count: 3, OAM down retry count: 5

OAM Loopback status: OAM Disabled

OAM VC status: Not Managed

ILMI VC status: Not Managed

VC TxRingLimit: 78 particles

VC Rx Limit: 23 particles

InARP frequency: 15 minutes(s)

Transmit priority 4

InPkts: 65274143, OutPkts: 122803702, InBytes: 2202883304, OutBytes: 2608861576

InPRoc: 343425, OutPRoc: 481284

InFast: 64930718, OutFast: 122322494, InAS: 0, OutAS: 0

InPktDrops: 0, OutPktDrops: 7319001/0/7319001 (holdq/outputq/total)

InByteDrops: 0, OutByteDrops: 0

CrcErrors: 1954, SarTimeOuts: 0, OverSizedSDUs: 528, LengthViolation: 0, CPIErrors: 0

Out CLP=1 Pkts: 0

OAM cells received: 81

F5 InEndloop: 0, F5 InSegloop: 0, F5 InAIS: 81, F5 InRDI: 0

F4 InEndloop: 0, F4 InSegloop: 0, F4 InAIS: 0, F4 InRDI: 0

OAM cells sent: 81

F5 OutEndloop: 0, F5 OutSegloop: 0, F5 OutRDI: 81

F4 OutEndloop: 0, F4 OutSegloop: 0, F4 OutRDI: 0

OAM cell drops: 0

Status: UP

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