3Com 4007, Руководство по внедрению, Страница: 380 / 684

380 C
HAPTER
16: IP R
OUTING
Broadcast Address
You can set a broadcast address for each defined IP interface. Your
module uses this broadcast address when forwarding directed broadcast
packets, and when advertising RIP packets.
When you define an IP interface, the broadcast address is
255.255.255.255. This is the default address.
Important
Considerations
Keep the following points in mind when you use broadcast address:
■
You cannot change the broadcast address for an IP interface if you
have already defined any RIP advertisement addresses.
■
If you are concerned with security, filter all inbound and outbound
broadcast traffic. Many hosts are set up to respond to an echo request
to their broadcast address with an echo reply, which can breach
security.
Directed Broadcast
A directed broadcast contains 1s in the host portion of the address field.
You can choose to have your module, on a per-interface basis, enable or
disable the forwarding of directed broadcast frames.
Important
Considerations
Keep the following points in mind when you use directed broadcast:
■
When your module receives a directed broadcast and the destination
is different from the interface on which it was received:
■
Your module forwards the directed broadcast if directed broadcast
is
enabled
■
Your module drops the directed broadcast if directed broadcast is
disabled
■
Set the directed broadcast to reflect your security requirements. If you
have a critical IP interface, disabling directed broadcast can, for
example, protect against denial-of-service attacks by malicious users.
Routing
Information
Protocol (RIP)
RIP is the protocol that implements routing. RIP does this by using
Distance Vector Algorithms (DVAs) to calculate the route with the fewest
number of hops to the destination of a route request. Each device keeps
its own set of routes in its routing table. RIP is an Interior Gateway
Protocol (IGP) for TCP/IP networks.