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28 Cards in this Set
- Front
- Back
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OSPF
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Open Shorted Path First
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IS-IS
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Intermediate System to
Intermediate System |
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configure OSPF
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Basic OSPF operations can be configured with a
router ospf process-id and a network statement |
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shortest path first (SPF) algorithm
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Dijkstra's algorithm is commonly referred to as the shortest path first (SPF) algorithm
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how does a link-state routing protocol work?
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1. Each router learns about its own links, its own directly connected networks
2. exchange hello packets to meet neighbors on directly connected networks 3. each router builds a link state packet (LSP) containing the state of each directly connected link. 4.each router floods the LSP to all neighbors to store in the receiver's database and forward on to its neighbors. 5.each router uses the db to create a topology of the network and create the beat path to each destination network. |
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what does LSP contain
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neighbor ID,
link type, bandwidth |
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what is a link
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an interface on a router
the interface must be up and should be in one of the network statements |
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what is a link state
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information about the state of the interface:
contains: IP and subnet mask type of network (ethernet or serial point to point link) cost of the link any neighbor routers on that link |
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learning about directly connected networks
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-learn about the the interface and the state of the link
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neighbor on directly connected network
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the next hop that's running OSPF
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adjacency
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when two routers learn they are neighbors, they form adjancency.
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LSP
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each router builds an LSP containing the state of each directly connected interface.
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flooding LSP to neighbors
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each router floods the link state info to all other link state routers in the routing area. When a router receives an LSP from a neighbor, it sends the LSP out all other interfaces except the interface it received it.
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when is an LSP sent
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-during initial startup of the router or during the configuration of the routing protocol on the router
-when there is a change in topology |
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what is in an LSP
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-link state information
-sequence numbers -aging information the extra info other than link state is used to determine if the received LSP has new information or if that LSP is already present in it's database |
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what is the SPF algorithm used for
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to construct the topology of the netowrk area and compute the best path to each destination.
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generating the routing table from the SPF tree
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using the shortest parth info determined from the SPF, the path can be added to routing table.
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advantages
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topological map
fast convergence event driven updates hierarchical design |
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topological map
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is created using the SPF tree
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fast convergence
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b/c flooding happens first and then the SPF is calculated after, convergence happens faster
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event driven updates
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LSP happens only when there is a change in topology.
OSPF udate happens every 30 minutes. |
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heirarchical design
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Link-state routing protocols such as OSPF and IS-IS use the concept of areas. Multiple areas create a hierarchical design to networks, allowing for better route aggregation (summarization) and the isolation of routing issues within an area
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areas
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-used to reduce the size of the link-state databases
-Multiple areas can also limit the amount of link-state information flooding in a routing domain and send LSPs only to those routers that need them. |
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how does areas work
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-nly those routers in the affected area receive the LSP and run the SPF algorithm. This can help isolate an unstable link to a specific area in the routing domain.
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inter area updates
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Routers in other areas will learn that a route in another network is down, but this will be done with a type of link-state packet that does not cause them to rerun their SPF algorithm. Routers in other areas can update their routing tables directly.
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requirements
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-more memory
-more CPU processing -sometimes requires more bandwidth than distance vector protocols. |
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OSPF
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-designed by IETF
-OSPF for IPv4 -OSPF for IPv6 |
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IS-IS
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IS-IS was designed by ISO
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