Recreating Late collisions

[Sibi Antony]

HP OpenCall faces an issue with one of our customers wherein we saw a very high late collision count. The HPUX build is 11iv1. From the lanadmin output the Duplex mode seems to be HDplx, with Auto Nego. set to ON.

Here is the lanadmin output.

PPA Number = 3
Description = lan3 HP A5506B PCI 10/100Base-TX 4 Port [100BASE-TX,HD,AUTO,TT=
Type (value) = ethernet-csmacd(6)
MTU Size = 1500
Speed = 100000000
Station Address = 0x306e25947d
Administration Status (value) = up(1)
Operation Status (value) = up(1)
Last Change = 478
Inbound Octets = 2985218406
Inbound Unicast Packets = 1539151128
Inbound Non-Unicast Packets = 1922516
Inbound Discards = 0
Inbound Errors = 0
Inbound Unknown Protocols = 84
Outbound Octets = 4127381116
Outbound Unicast Packets = 2724403576
Outbound Non-Unicast Packets = 295857
Outbound Discards = 0
Outbound Errors = 0
Outbound Queue Length = 0
Specific = 655367

Ethernet-like Statistics Group

Index = 3
Alignment Errors = 0
FCS Errors = 0
Single Collision Frames = 50396204
Multiple Collision Frames = 1699987
Deferred Transmissions = 80177595
Late Collisions = 35657510
Excessive Collisions = 0
Internal MAC Transmit Errors = 0
Carrier Sense Errors = 0
Frames Too Long = 0
Internal MAC Receive Errors = 0

We are trying to recreate a similar scenario in lab for tests etc. But I am not sure how can we recreate the late collisions. I can see collision frame counts while configuring the host in AUTO_NEG ON, and setting the switch port to HD and pumping some traffic through this interface. However, no late collisions could be seen so far. From hp docs page ( http://docs.hp.com/en/J5683-90017/apds01.html ), late collisions is defined to be "the number of times that a collision is detected on a particular interface later than 512 bit-times into the transmission of a packet". In what all scenarios we can see collision on the same packet after 512 bit-time.

[VK2COT]

Hello,

It is almost certain that the port on the
switch/router end is set not to auto-negotiate.

Most of the time, late collisions are
caused by different settings on the server
and switch/router side.

Your problem sounds like a duplex and/or auto-negotiate mismatch between the server
and the switch/router port.

What you set on the HP-UX server side
is only one half of the set up. Check
the other side of the link.

Cheers,

VK2COT