Printing devices losing connectivity in 92% full vlan.

[larrydbrown]

I have around 50 vlans, of which 25 have dhcp scopes w/ the protocols dhcp and bootp enabled. Printing devices in an almost full vlan lose connectivity after x amount of seconds (<300 sec.). These devices are in scopes with dhcp enabled, if I take out the devices and place them in a vlan w/ < 100 and no dhcp/bootp enabled the device never loses connectivity. Before I move to place a sniffer on the vlan I would like to know if anyone has seen this b/4. Also, I have noticed that the only devices that are affected by this problem are 10 half cards in the hps printing devices. It seems the newer 10/100 h/full cards do not exhibit theses symptoms in a congested vlan. I am also moving to break up my vlans that are excessively full to a more moderate broadcast domain. Is there a recommended % or number of clients you should attempt to place in vlans? Any insight would be appreciated. Thanks.

[konigl]

How "full" are your VLANs? Sounds like the 10-half HP JetDirect cards are waiting and waiting and waiting and dropping off. Any chance you can check their software rev., maybe an update will fix. Are they getting their IP addresses via DHCP, or are they statically configured? Are the 10-half cards plugged into switchports that are also hard-coded to 10-half? (Maybe it's a speed/duplex issue.)

I don't remember ever hearing of something like this. What happens if you run a perpetual ping against the printer's IP address? Does it stay up? Or does it drop out? Is the timeframe for drop-out consistent?

Cisco Press's book "Top Down Detwork Design" (page 103) recommends the following maximum sizes for broadcast domains (VLANs), based on desktop protocols in use:

IP - 500 workstations (reduce to 200 if users are running multimedia apps, have high-bandwidth plus low-delay requirements, and/or high level of broadcast or multicast packets)

NetWare (IPX) - 300 workstations

AppleTalk - 200 workstations

NetBIOS - 200 workstations

Mixed (any of the above) - 200 workstations

Per the same book (p.102), if more than 20% of the network traffic is broadcasts or multicasts, then the network needs to be segmented.

Make your VLANs no bigger than a Class C IP netmask (255.255.255.0 or /24) and this should help control broadcast volume.

Hope this helps.

[DWAM_2]

Absolute usefull anwser !

Thank you.

[larrydbrown]

I have updated the jetdirect cards to their most recent revs. The IPs are statically assigned and I have hard coded the speed/duplex to 10/half on the faste interface they are connected to.

If I run a constant ping to the devices they never drop. The puzzling part of this problem is when I change the vlan assignment the device never drops. It is important to note that the vlan I am adding it to does not have dhcp scope assigned, so all the devices are static. When I add it back to the native vlan, for that closet, which has a dhcp scope it drops. Thanks in advance.

[konigl]

On the VLAN with DHCP active, does your printer's IP address fall within the DHCP scope range? It sounds like maybe some other station is getting a duplicate IP address via DHCP, and they may be stepping on each other. Maybe the JetDirect's response to that is to just stop talking on the LAN.

If that is the case, either assign the printer an address outside of the DHCP scope, or exclude that IP address from being handed out from within DHCP server. Restart the printer.

One way to check for duplicate IP address is, to ping that IP address from another VLAN or subnet after the printer seems to have dropped out. Then go into a router or Layer 3 switch that directly connects to the VLAN which has DHCP. Do a "show ip arp" and look for the IP address of the printer. Does that MAC address match the one on the printer's JetDirect card?

Hope this helps.