What happens to local braodcasts when default gateway fails
Senario: Windows XP machines on a LAN (10.25.20.x/16) with gateway 10.25.20.1. The gateway recently failed causing severe delays in local network communication. I am trying to determine how WinXP sends traffic when the default gateway is offline. I was under the impression that a system will automatically broadcast LAN traffic without sending it to the default gateway. Will WinXP always send data to the default gateway even if it is intended for a device on the same subnet (10.25.20.10 sends data to 10.25.20.11 for example). If this is the case, is there a way to have XP know to broadcast or send the data to the device directly without involving the default gateway?
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
How many machines do you actually have on that /16, it's not normal to have a mask of that kind of size. If it's a lot you might find that you were rather a lot of ARP requests broadcasting over the network when the local caches timed out and that might have been enough to swamp a switch or link.
It's also possible that your default gateway device dying triggered some spanning tree issues which again could have impacted the local network badly. It depends on what that device was and on your design.
It's also possible that your default gateway device dying triggered some spanning tree issues which again could have impacted the local network badly. It depends on what that device was and on your design.
ASKER
thank you for the responses, they gave me some ideas on what could be causing the problem. I do have active directory setup and it communicates across a VPN. That means any DNS lookups have to route via the VPN. I will play with these setting and update the post when i have confirmed that is the problem.
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
Just to add to the above comments
Local communication should not be affected if the Gateway is lost however WINS and DNS resolution could be impacted causing delays in local communication
Have a read of this link and related it to you setup; i.e. placement of WINS/DNS servers? resources affected did they need WINS resolution? etc etc
http://www.tech-faq.com/netbios-node-types.html
Local communication should not be affected if the Gateway is lost however WINS and DNS resolution could be impacted causing delays in local communication
Have a read of this link and related it to you setup; i.e. placement of WINS/DNS servers? resources affected did they need WINS resolution? etc etc
http://www.tech-faq.com/netbios-node-types.html
..... how are your clients resolving Names? are they p,h,n or m nodes ? etc etc
Firstly, broadcast messages are not carried from one network to another, they are meant for the same collision domain. So for your case, the broadcast message will be sent to all the machines in the domain as well as the default gateway. Whether default gateway is down or not is not a matter of concern for the sender.
Now if the packet is meant for a specific IP Address, then things are a bit different.
Supposing the sender and the receiver are in the same collision domain, the packet goes directly from the sender to the receiver without having to go through the default gateway. This communication is looked after by the intermediate switch that keeps a MAC table, wherein the switch is aware of the two PC's being connected to it. If there is no presence of the Receiver in the MAC Table, it looks for the update of the MAC Table and if it still does not find the Receiver, it sends the packet to the default gateway.
The problem if the default gateway is down is that you won't have access to the internet. So if you say you receive DNS via VPN, it makes internet connection essential for DNS Queries.
Hope it helps.
Now if the packet is meant for a specific IP Address, then things are a bit different.
Supposing the sender and the receiver are in the same collision domain, the packet goes directly from the sender to the receiver without having to go through the default gateway. This communication is looked after by the intermediate switch that keeps a MAC table, wherein the switch is aware of the two PC's being connected to it. If there is no presence of the Receiver in the MAC Table, it looks for the update of the MAC Table and if it still does not find the Receiver, it sends the packet to the default gateway.
The problem if the default gateway is down is that you won't have access to the internet. So if you say you receive DNS via VPN, it makes internet connection essential for DNS Queries.
Hope it helps.
ASKER
I still have not been able to test any of the offered solutions. I am writing to keep the case open until i can get something scheduled. the difficulty is that is problem is with a 24/7 environment that never has a window for downtime.
on the pc that is having issues type
route print
and see if it is routing anything via the gateway