[nsp] ATM problems (DSL)

[Charles Sprickman]

Hi,

I've been working with Covad for the last week on a mysterious problem
that we're seeing on some of our bridged ADSL customers.  A brief
description of our setup follows:

-DSL through Covad; they provide a DS3 ATM handoff.  One PVC per customer,
both ADSL and SDSL.
-Approximately 1000 PVCs.
-ADSL customers setup with straight bridging via BVIs.
-PA-A3-T3 ATM card
-IOS 12.2(8)T5 on a 7206 VXR w/NPE-300

The problem we're seeing is that out of hundreds of bridged ADSL
customers, we have about a dozen that complain of stalled page loads, low
transfer rates via ftp, and dns timeouts.  We've tracked this (using
smokeping) to a sporadic packet loss problem on these customers.  We are
seeing a consistent 5-20% packet loss.  The RTT of the pings remains
constant, which is familiar to me as cell loss.

Now this is likely a Covad problem, but they have re-routed these pvcs,
and done whatever testing they can do, but they are not able to tell me
where the drops are occuring.  In the meantime, I wanted to post a query
here to see if there's any possibility of a problem on our side.  There
are quite the wealth of black-magic atm commands that I'm not going to
diddle unless there's good reason.

Below are some config snippets:

(main atm interface config)
!
interface ATM2/0
 description Covad ATM DS-3 Interface for DSL
 mtu 1500
 no ip address
 no ip proxy-arp
 load-interval 30
 atm scrambling cell-payload
 atm framing cbitplcp
 atm uni-version 3.1
 no atm auto-configuration
 no atm ilmi-keepalive
 no atm address-registration
 no atm ilmi-enable
 arp arpa
 arp timeout 900
!
(sub int for one adsl block)
interface ATM2/0.3 multipoint
 description static ADSL 1 (98/24)
 map-group static-adsl
 atm pvc 72 0 72 aal5snap
 atm pvc 1025 0 1025 aal5snap
 atm pvc 1027 0 1027 aal5snap
[etc...]
!
(bridge group config)
bridge-group 2
 bridge-group 2 spanning-disabled
!
bridge 2 protocol ieee
bridge 2 route ip
!
(bvi config)
!
interface BVI2
 description BVI for static ADSL customers
 mac-address 0000.0cd1.4604
 mtu 1500
 ip address x.x.98.1 255.255.255.0
 no ip redirects
 ip local-proxy-arp
 ip route-cache same-interface
 load-interval 30
 arp timeout 60
!

And some stats:

(counters reset about 30 hours ago)
ATM2/0 is up, line protocol is up
  Hardware is ENHANCED ATM PA
  Description: Covad ATM DS-3 Interface for DSL
  MTU 4470 bytes, sub MTU 1500, BW 40704 Kbit, DLY 190 usec,
     reliability 255/255, txload 57/255, rxload 52/255
  Encapsulation ATM, loopback not set
  ARP type: ARPA, ARP Timeout 00:15:00
  Encapsulation(s): AAL5
  4095 maximum active VCs, 1242 current VCCs
  VC idle disconnect time: 300 seconds
  0 carrier transitions
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 1d03h
  Input queue: 1/75/1970/76914 (size/max/drops/flushes); Total output
drops: 109
  Queueing strategy: None
  30 second input rate 8359000 bits/sec, 1976 packets/sec
  30 second output rate 9221000 bits/sec, 2199 packets/sec
     235548853 packets input, 909145453 bytes, 3171 no buffer
     Received 140152 broadcasts, 0 runts, 10008 giants, 0 throttles
     6401 input errors, 6401 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     266868767 packets output, 2572263653 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out

router.bway.net#sh in bvi 2
BVI2 is up, line protocol is up
  Hardware is BVI, address is 0000.0cd1.4604 (bia 0000.0000.0000)
  Description: BVI for static ADSL customers
  Internet address is 216.220.98.1/24
  MTU 1500 bytes, BW 40704 Kbit, DLY 5000 usec,
     reliability 255/255, txload 7/255, rxload 5/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 00:01:00
  Last input 2w5d, output never, output hang never
  Last clearing of "show interface" counters 00:22:50
  Input queue: 1/75/1167/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/0 (size/max)
  30 second input rate 852000 bits/sec, 317 packets/sec
  30 second output rate 1217000 bits/sec, 288 packets/sec
     432323 packets input, 123017327 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
     439041 packets output, 272346880 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out

Thanks,

Charles

--
Charles Sprickman
spork at inch.com