Comware

Hey all -

I have just been assigned to a network that has a HP2824 procurve managed switch. The management console reports "excessive late collisions" about every 15 minutes and "excessive CRC/alignment errors" every few hours approximately, on port 5 only.

The device at the other end of port 5 is a Netgear 4-port hub that apparently serves as a DMZ on the network. So, this port 5 is delivering the "firewalled" external traffic to and from the LAN.

The port was configured to auto-negotiate, and was running at 10HDx, which I think would be correct for this little 10Mb/s hub (802.3 also, which means half-duplex, right?)

The cable for this port is the same type used on all other ports, most of which are running at 100 or 1000Mb/s...

Users report that their connections get dropped from time to time, and the in-house admin reports that these people are on a Netgear 24-port Gb switch (not the hub mentioned above) that is uplinked from the HP2824, and their connectivity is restored when moving them to a different port of the Netgear switch. I think these 2 issues are probably unrelated, I only mention it b/c I am not sure...

The issue I am concerned with now is the late collisions/CRC errors reported. Any ideas are greatly appreciated.

A few minutes ago I changed the port config from auto to forced 10HDx (the same setting that was auto-negotiated) based on some other thread I read about "late collisions" issue... I will report again at the end of day today. Thanks again.

Chris M.

Get rid of the mini-hub. For the sake of the few extra ports it gets you, it just is not worth it. I have made it my quest to rid the world of those pesky little unmanaged critters.

Your errors are probably not on the switch side of the connection but rather one of the hub ports or one of the other devices connected to the hub.

I'm not too fond of that device either, but we actually only need 3 ports for this DMZ, so recommending an upgrade would be difficult (unless you know of a good managed gigabit 4 port switch...) :)

The other two devices on this hub are the router, and a linux box used for monitoring net traffic (hence the need to be outside the firewall).

Thanks for the reply. Please keep the ideas coming, in the meantime I'll see if we can bypass the hub for a while.

Why you do not change this HUB to a little 4/5 Port SWITCH which will cost only about (I think) 25 to 50 $.

Chris,

sounds indeed like a speed / duplex mismatch on this port. By default, most devices will autonegotiate the correct setting regardless of the speed, that is set before autonegotiation happens (sppedsense). Here however is where the issue is, if you have a unmanagable device like that hub, most likley you cannot make any settings and some of those cheapies do weired stuff. I would do some "research" to find the default setting for the hub ports and configure the switch accordingly. The half duplex you see could also be happen when autonegotiation fails and the device reverts to the lowest common setting - hence half duplex. Now, if you hub would do Full but won't autoneg then that setting is wrong. Again, either find the documentation or try the avail. combinations, sorry that it is not easier..... Oh ja, one way to around that hub would be to have two interfaces in your Linux box and go in interface one and out number two. I remember fixing a similar issue some time ago where they had a hub as well to inspect traffic and nothing but trouble - maybe that is an option for you.

Regards

GG

Thanks again for the replies. I will see what I can do about doing away with the hub.

Chris - if it was helpful please assign some points to the answers. Thanks

GG

Ja, I only need 528 more points to make it to #1 :)

If the Linux net monitoring box is used as a sniffer (e.g. together with Snort or Ntop), you will need a switch with port mirroring/SPAN functionality to replace the hub.

A hub will forward all packets to all ports. A switch only forwards a packet on the switchport connecting the receiving host.

Regards
Regnar

The 2800 supports ingress/egress port mirroring. You could place your sniffer on the monitor port and mirror all traffic in/out the router port.

Thanks for all the ideas fellas. I only get to this site about once per week, so I'll try to implement some of your suggestions over the next few weeks, update status and award points based of results. Thanks again.