Radware Alteon, Инструкция по применению

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Alteon Application Switch Operating System Application Guide
Open Shortest Path First (OSPF)
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Document ID: RDWR-ALOS-V2900_AG1302
The BDR is adjacent to all other neighbors (including the DR). Each neighbor sends its database
information to the BDR just as with the DR, but the BDR merely stores this data and does not
distribute it. If the DR fails, the BDR takes over the task of distributing database information to the
other neighbors.
Note: The Alteon IPv6 component runs OSPFv3 adjacency per VLAN and not per Layer 3 interface.
This is because OSPFv3 requires a link local address, which is available with a VLAN, but not with a
Layer 3 interface.
The Link-State Database
OSPF is a link-state routing protocol. A link represents an interface (or routable path) from the
routing device. By establishing an adjacency with the DR, each routing device in an OSPF area
maintains an identical Link-State Database (LSDB) describing the network topology for its area.
Each routing device transmits a Link-State Advertisement (LSA) on each of its interfaces. LSAs are
entered into the LSDB of each routing device. OSPF uses flooding to distribute LSAs between routing
devices.
When LSAs result in changes to the routing device's LSDB, the routing device forwards the changes
to the adjacent neighbors (the DR and BDR) for distribution to the other neighbors.
OSPF routing updates occur only when changes occur, instead of periodically. For each new route, if
an adjacency is interested in that route (for example, if configured to receive static routes and the
new route is indeed static), an update message containing the new route is sent to the adjacency.
For each route removed from the routing table, if the route has already been sent to an adjacency,
an update message containing the route to withdraw is sent.
The Shortest Path First Tree
The routing devices use a link-state algorithm (Dijkstra's algorithm) to calculate the shortest path to
all known destinations, based on the cumulative cost required to reach the destination.
The cost of an individual interface in OSPF is an indication of the overhead required to send packets
across it. The cost is inversely proportional to the bandwidth of the interface. A lower cost indicates
a higher bandwidth.
Internal versus External Routing
To ensure effective processing of network traffic, every routing device on your network needs to be
configured to correctly send a packet (directly or indirectly) to any other location or destination in
your network. This is referred to as internal routing, and can be done with static routes or using
active internal routing protocols, such as the Routing Information Protocol (RIP), RIPv2, and the
Open Shortest Path First (OSPF) protocol.
It is also useful to expose the routes you can access outside your network (upstream providers or
peers) about the routes you have access to in your network. Sharing of routing information between
autonomous systems is known as external routing.
Typically, an AS has one or more border routers (peer routers that exchange routes with other OSPF
networks) as well as an internal routing system enabling every router in that AS to reach every
other router and destination within that AS.
When a routing device advertises routes to boundary routers on other autonomous systems, it is
effectively committing to carry data to the IP space represented in the route being advertised. For
example, if the routing device advertises 192.204.4.0/24, it is declaring that if another router sends
data destined for any address in the 192.204.4.0/24 range, it will carry that data to its destination.