[c-nsp] IP packet out of order.

[mezibra adel]

Hi,

I remember that the PA-A3 uses two segmentation and reassembly chips (2 SARs
for transmit and recept) from LSI Logic (ATMizer II). 

Each SAR has four separates FIFO to maximize the performance of simultaneous
read/write operations.

I could be wrong but I guess that when Ethernet/IP packets arrive at ATM
Adaptation Layer the 38 bytes packet is processed/split into 53 bytes ATM
cells and ready to transfert faster than the 1400 bytes packets.

What is the behaviour of your test with different packet size for the 2nd
packet (say 44,580, 1420)

What is you Ethernet/ATM bridge hardware?

Adel Mezibra

-----Message d'origine-----
De : cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] De la part de Olivier Gosselet
Envoyé : vendredi 23 juillet 2004 19:13
À : cisco-nsp at puck.nether.net
Objet : [c-nsp] IP packet out of order.

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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