Which Debug to use?

[snootalope]

hello

Cisco 1751 Router - IOS 12.2(15)ZJ2

I've got a serial interface that is having some very random dropped packets in it's default priority queue. I'd like to know exactly what those drops are, but I don't want to enable the "debug ip packet" or something like that and let it run till it drops packets cause it's totally random. Could be every 5 minutes, could be every other hour..

Is there an alternative to the debug command to view which packets it's actually dropped?

Thanks!

 

[directlyconnected]

Post a show int Serial(whatever). Need to know runts, giants, supergiants, throttles, babbles, etc, what laqyer 2 protocol, etc. Also post a sh run, or post the router uptime, so we know how long the packets have been going thru. Show interface serial(whatever) detail would be good, too. A logging command may be your best bet...

 

[snootalope]

Show Int S0/0:

Serial0/0 is up, line protocol is up
Hardware is PQUICC with Fractional T1 CSU/DSU
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 22/255, rxload 41/255
Encapsulation FRAME-RELAY, loopback not set
Keepalive set (10 sec)
LMI enq sent 6767, LMI stat recvd 6767, LMI upd recvd 0, DTE LMI up
LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0
LMI DLCI 0 LMI type is ANSI Annex D frame relay DTE
FR SVC disabled, LAPF state down
Broadcast queue 0/64, broadcasts sent/dropped 0/0, interface broadcasts 0
Last input 00:00:03, output 00:00:00, output hang never
Last clearing of "show interface" counters 18:47:51
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1338
Queueing strategy: dual fifo
Output queue: high size/max/dropped 0/256/0
Output queue: 0/128 (size/max)
30 second input rate 254000 bits/sec, 105 packets/sec
30 second output rate 136000 bits/sec, 118 packets/sec
10010363 packets input, 1590347999 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
13303822 packets output, 1729556491 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


Show policy interface:

Serial0/0.16: DLCI 16 -

Service-policy output: QoS-Policy

Class-map: VoIP-RTP (match-all)
526261 packets, 106998995 bytes
30 second offered rate 81000 bps, drop rate 0 bps
Match: access-group 105
Queueing
Strict Priority
Output Queue: Conversation 72
Bandwidth 500 (kbps) Burst 12500 (Bytes)
(pkts matched/bytes matched) 526261/87169436
(total drops/bytes drops) 0/0

Class-map: class-default (match-any)
8576970 packets, 1765647356 bytes
30 second offered rate 320000 bps, drop rate 0 bps
Match: any
Queueing
Flow Based Fair Queueing
Maximum Number of Hashed Queues 64
(total queued/total drops/no-buffer drops) 0/315/0

Thanks for your help!! I've been struggling with this forever!!

 

[directlyconnected]

Fractional T1, frame relay---what bandwidth does the telco guarantee? If it's 768, then maybe try lowering the bandwidth on the serial interface to whatever the max guaranteed bw from the telco is. Other than that, you got me! Sorry.

Tim

 

[jneiberger]

Do you really need to know what is being dropped? If something is being dropped that shouldn't be, put it in a higher-priority queue.

What you're demonstrating is that your queue configuration is working. At some point, there is more traffic to transmit that there is bandwidth available. Something must be dropped, so the router is passing your high priority traffic while dropping some traffic from the default queue.

This is the expected behavior, and it's especially irrelevant if the traffic being dropped is TCP, since those packets will be retransmitted by the sending host. Why do you need to know precisely which packets are being dropped?

 

[snootalope]

Yeah, i'd really like to know what's being dropped. I've got a number of services using the link and im having trouble with disconnected sessions, incomplete faxes, echo during voip calls and other small issues. As you can see, ive got priority queues setup for VoIP traffic, which is by far the most important service.

I'd just really like to see exactly whats being dropped so i can get it into its own queue with a piece of reserved bandwidth or whatever..

 

[jneiberger]

I asked about this somewhere else and got a really good idea. Does your router support NetFlow switching? If so, turn it on by using "ip route-cache flow" on all interfaces, not just the interface you want to watch. Then, do a "show ip cache flow" and look for packets destined for a Null0 interface: those are your dropped packets.

Let me know if it works for you.

John

 

[snootalope]

yeah.. it does support Netflow, i had that on there for a while. I'll check it out, thanks!