[c-nsp] IP packet out of order.

[Siva Valliappan]

are you CEF switching?  if you are not CEF switching, it is technically
possible to get OOP due to the router.  reason is as follows:

first packet builds the fast cache entry, and if the second packet comes
close enough on the heels of the first packet, the second packet
might get switched on the interrupt path before the first packet gets
it's new header and is placed on the transmit interface.

now the above only happens with fast switching.  in the case of CEF,
the forwarding table is built on the routing table, so the first packet
does not need to trigger the construction of the forwarding table.

if you are getting OOP all the time (regardless of wether you are
running CEF or if you are having OOP even with a cache entry built),
then you might want to start investigating what the bridging
device is doing.

cheers
.siva

On Fri, 23 Jul 2004, Olivier Gosselet wrote:

> Hi all,
>
> I have the following setup :
>
> Router A - Ethernet LAN - Bridge Eth/ATM - ATM Network - Router B - Ethernet
> LAN
>
> IP packet 1 - 1400 Bytes
> IP packet 2 - 38 bytes
>
> All routers ethernet interfaces are FIFO ...
>
> Packets are sent out by router A to router B in the following order : 1 - 2
> Packets are sent out by router B onto the LAN in the following order : 2 - 1
>
> According to my understanding of "IP over ATM" IP Packet are chopped into
> ATM cells with IP Packet 1 contained into several ATM cells while IP Packet
> 2 fits into 1 cell.
> I know there is only one physical path in the ATM network from the bridge to
> the router. I have no control on the ATM Bridge and/or Network but I would
> assume they send and transport the resulting cells on a FIFO basis meaning
> all the cell of packet 1 followed by the cell of packet 2.
> Would there be any chances that the Router B dequeues the second packet
> first while the ATM cells were all received in the correct order.
>
> Router 2 is a cisco 7206VXR (NPE400)
>
> Slot 2:
>         ATM WAN OC3 (MM) Port adapter, 1 port
>         Port adapter is analyzed
>         Port adapter insertion time 1w0d ago
>         EEPROM contents at hardware discovery:
>         Hardware revision 2.0           Board revision A0
>
>         Serial number     20666702      Part number    73-2430-04
>         FRU Part Number:  PA-A3-OC3MM=
>
> interface ATM2/0
>  description To ATM switch
>  no ip address
>  load-interval 30
>  no atm ilmi-keepalive
>
> interface ATM2/0.x point-to-point
>  description Cisco A to Cisco B
>  ip address x.y.240.73 255.255.255.252
>  ip mtu 1500
>  ip ospf network broadcast
>  atm route-bridged ip
>  pvc Cisco A 12/800
>   vbr-nrt 8000 8000
>   encapsulation aal5snap
>
> Your idea on this one would be highly appreciated.
>
> Regards,
>
> Olivier
>
>
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