Udp Broadcast Packets And Protocols - Cisco Catalyst 9500 series Configuration Manual

Broadcast Packet Handling
merely keeps track of which systems are sending the data. The advantage of using IRDP is that it allows each
router to specify both a priority and the time after which a device is assumed to be down if no further packets
are received.
Each device discovered becomes a candidate for the default router, and a new highest-priority router is selected
when a higher priority router is discovered, when the current default router is declared down, or when a TCP
connection is about to time out because of excessive retransmissions.

UDP Broadcast Packets and Protocols

User Datagram Protocol (UDP) is an IP host-to-host layer protocol, as is TCP. UDP provides a low-overhead,
connectionless session between two end systems and does not provide for acknowledgment of received
datagrams. Network hosts occasionally use UDP broadcasts to find address, configuration, and name
information. If such a host is on a network segment that does not include a server, UDP broadcasts are normally
not forwarded. You can remedy this situation by configuring an interface on a router to forward certain classes
of broadcasts to a helper address. You can use more than one helper address per interface.
You can specify a UDP destination port to control which UDP services are forwarded. You can specify multiple
UDP protocols. You can also specify the Network Disk (ND) protocol, which is used by older diskless Sun
workstations and the network security protocol SDNS.
By default, both UDP and ND forwarding are enabled if a helper address has been defined for an interface.
The description for the ip forward-protocol interface configuration command in the Cisco IOS IP Command
Reference, Volume 1 of 3: Addressing and Services lists the ports that are forwarded by default if you do not
specify any UDP ports.
Broadcast Packet Handling
After configuring an IP interface address, you can enable routing and configure one or more routing protocols,
or you can configure the way the Device responds to network broadcasts. A broadcast is a data packet destined
for all hosts on a physical network. The Device supports two kinds of broadcasting:
• A directed broadcast packet is sent to a specific network or series of networks. A directed broadcast
• A flooded broadcast packet is sent to every network.
Routers provide some protection from broadcast storms by limiting their extent to the local cable. Bridges
(including intelligent bridges), because they are Layer 2 devices, forward broadcasts to all network segments,
thus propagating broadcast storms. The best solution to the broadcast storm problem is to use a single broadcast
address scheme on a network. In most modern IP implementations, you can set the address to be used as the
broadcast address. Many implementations, including the one in the Device, support several addressing schemes
for forwarding broadcast messages.
Routing Configuration Guide, Cisco IOS XE Everest 16.6.x (Catalyst 9500 Switches)
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address includes the network or subnet fields.
You can also limit broadcast, unicast, and multicast traffic on Layer 2 interfaces by
Note
using the storm-control interface configuration command to set traffic suppression
levels.
Configuring IP Unicast Routing