Broadcast Storms in Software

Drawer UPC-A in Software Broadcast Storms

A broadcast storm is the result of one or more devices sending a non-stop flurry of broadcast frames on the network The first sign of a broadcast storm is when every computer on the broadcast domain suddenly can t connect to the rest of the network There are usually no clues other than network applications freezing or presenting can t connect to types of error messages Every activity light on every node is solidly on Computers on other broadcast domains work perfectly well The trick is to isolate; that s where escalation comes in You need to break down the network quickly by unplugging devices until you can find the one causing trouble It s usually difficult to get a packet analyzer to work, but at least try If you can scoop up one packet you ll know what node is causing the trouble The second the bad node is disconnected, the network returns to normal But if you have a lot of machines to deal with and a bunch of users who can t get on the network yelling at you, you need help Call a supervisor to get support to solve the crisis as quickly as possible

A switching loop is when you connect multiple switches together to cause a loop to appear Switching loops are rare because most switches use the spanning tree protocol, but they do happen The symptoms are identical to a broadcast storm: every computer on the broadcast domain can no longer access the network

The good part about switching loops is that they rarely take place on a well-running network Someone had to create that loop and that means someone, somewhere is messing with patch cables Escalate the problem and get the team to help you find the person making changes to the switches

Improperly configured routers aren t going to send packets to the proper destination The symptoms are clear: every system that uses the misconfigured router as a default gateway is either not able to get packets out or get packets in, or sometimes both Web pages don t come up, FTP servers suddenly disappear, and e-mail clients can t access their servers In these cases you need to verify first that everything under your responsibility works If that is true, then escalate the problem and find the person responsible for the router

A routing loop is when interconnected routers loop traffic, causing the routers to respond slowly or not respond at all Dynamic routing protocols sometimes cause routing loops when a router goes down, but most routing loops are from static routes Your big clue is a huge amount of traffic far more than your usual traffic on the links between the routers Router loops never cause individual computers to stop responding (unless they happen to be on the same broadcast domain as the looping packets) Like with any route problem, be able to recognize the symptoms and escalate

Proxy ARP is the process of making remotely-connected computers truly act as though they are on the same LAN as local computers Proxy ARPs are done in a number of different ways, with a Virtual Private Network (VPN) as the classic example If a laptop in an airport connects to a network through a VPN, that computer takes on the network ID of your local network In order for all this to work, the VPN concentrator needs to allow some very LAN-type traffic go through it that would normally never get through a router ARP is a great example If your VPN client wants to talk to another computer on the LAN, it has to ARP to get the IP address Your VPN device is designed to act as a proxy for all that type of data Almost all proxy ARP problems take place on the VPN concentrator With misconfigured proxy ARP settings, the VPN concentrator can send what looks like a Denial of Service (DoS) attack on the LAN (A DoS attack is usually directed at a server exposed on the Internet, like a Web server See 17, Protecting Your Network, for more details on these and other malicious attacks) If your clients start receiving a large number of packets from the VPN concentrator, assume a proxy ARP problem and escalate by getting the person in charge of the VPN to fix it

Troubleshooting Is Fun!

The art of network troubleshooting can be a fun, frolicsome, and frequently frustrating feature of your network career By applying a good troubleshooting methodology and constantly increasing your knowledge of networks, you too can develop into a great troubleshooting artist This takes time, naturally, but stick with it Begin the training