Adapted from Perlman's book) A broadcast storm is an event that causes a flurry of messages....

Transcribed Image Text:

Adapted from Perlman's book) A broadcast storm is an event that causes a flurry of messages. One implementation that caused broadcast storms was the Berkeley UNIX endnode IP implementation. In this implementation, an endnode attempts to forward a packet that it mysteriously receives with a network layer (IP) address that is different from itself. This is what you would do if you found a neighbor's letter wrongly placed in your mailbox. However, this seemingly helpful policy can cause problems. Consider the figure below which shows 2 LANs connected by a bridge, with several IP endnodes on each LAN. There are no IP routers. All IP endnodes are configured with the same mask and so can tell that they have the same net number/prefix. Suppose IP endnode A is incorrectly configured and incorrectly thinks its data link address is all 1's. The data link address of all 1's is the broadcast address: any packet sent to such an address is received by all stations on a LAN (it is the ultimate multicast address!). Bridge a) What happens when another IP endnode D decides to send a packet to IP endnode A? Assume that D initially does not have A's data link address in its cache, and so must do the ARP protocol. Give the sequence of events. b) Suppose the bridge is replaced by an IP router. (Of course, the masks at the nodes must be changed so that there are now two masks, one for each LAN. Note a mask is just a bitmap of I's in the most significant bits that tells you how long the prefix for that subnet is) The problem does not disappear, but it does get a little better. Explain as precisely as you can the improvement using two parameters: T the total number of endnodes in the network of Ethernets, and M the maximum number of endnodes in a single Ethernet. Adapted from Perlman's book) A broadcast storm is an event that causes a flurry of messages. One implementation that caused broadcast storms was the Berkeley UNIX endnode IP implementation. In this implementation, an endnode attempts to forward a packet that it mysteriously receives with a network layer (IP) address that is different from itself. This is what you would do if you found a neighbor's letter wrongly placed in your mailbox. However, this seemingly helpful policy can cause problems. Consider the figure below which shows 2 LANs connected by a bridge, with several IP endnodes on each LAN. There are no IP routers. All IP endnodes are configured with the same mask and so can tell that they have the same net number/prefix. Suppose IP endnode A is incorrectly configured and incorrectly thinks its data link address is all 1's. The data link address of all 1's is the broadcast address: any packet sent to such an address is received by all stations on a LAN (it is the ultimate multicast address!). Bridge a) What happens when another IP endnode D decides to send a packet to IP endnode A? Assume that D initially does not have A's data link address in its cache, and so must do the ARP protocol. Give the sequence of events. b) Suppose the bridge is replaced by an IP router. (Of course, the masks at the nodes must be changed so that there are now two masks, one for each LAN. Note a mask is just a bitmap of I's in the most significant bits that tells you how long the prefix for that subnet is) The problem does not disappear, but it does get a little better. Explain as precisely as you can the improvement using two parameters: T the total number of endnodes in the network of Ethernets, and M the maximum number of endnodes in a single Ethernet.

Answer rating: 100% (QA)

a What happens when another IP endnode D decides to send a packet to IP endnode A Assume that D initially does not have As data link address in its ca... View the full answer