The Route Table
Configuring Static Routes
Case Study: Simple Static Routes
Case Study: Summary Routes
Case Study: Alternative Routes
Case Study: Static Floating Routes
Case Study: Load Sharing
Case Study: Recursive Table Lookups
Troubleshooting Static Routes
Case Study: Tracing a Failed Route
Case Study: A Protocol Conflict
The router will match the most specific address it can. In descending order of specificity, the address may be one of the following:
A host address
A subnet
A group of subnets
A major network number
A group of major network numbers
A default address
The procedure for statically routing an internetwork has three steps:
1, For each data link within the internetwork, identify all addresses(subnet or network)
2, For each router, identify all data links not directly connected to that router
3, For each router, write a route statement for each data link not directly connected to it
By summarizing a group of subnets or even major networks, the number of static route entries may be reduced drastically. However, caution must be used when summarizing addresses; when done incorrectly, unexpected routing behavior may occur.
The administrative distances of all dynamic routing protocols are substantially higher than 1. Therefore, by default a static route to a network will always be prefered over a dynamically discovered route to the same network.
Per destination load balancing distributes the load according to destination address. Given two paths to the same network, all packets for one destination on the network may travel over the first path, all packets for a second destination on the same network may travel over the second path, all packets for a third destination may again be sent over the first path, and so on. This type of load balancing occurs in Cisco routers when they are fast switching, the default Cisco switching mode.
Per packet load sharing means that one packet to a destination is sent over one link, the next packet to the same destination is sent over the next link,and so on, given equal-cost paths. If the paths are unequal cost, the load balancing may be one packet over the higher-cost link for every three packets over the lower-cost link, or some other proportion depending upon the ratio of costs. Cisco routers will do per packet load balancing when they are process switching.
Check a router's ARP cached when packets do not go to the correct destination on a data link
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