IPv4 Addressing - Broadcast Addessing
What is Broadcast addressing?
Broadcast addressing is a method where a packet is sent from one device to all devices in a network segment simultaneously.
Why is Broadcast useful?
Broadcast is useful for network-wide announcements, such as ARP requests, DHCP discovery, and other services needing to reach all nodes.
How it works?
A device sends a packet to the broadcast address of the network (e.g., 255.255.255.255 or the subnet-specific broadcast address), and all devices on that subnet receive and process the packet.
Where is Broadcast used?
Broadcast is commonly used in IPv4 networks for services like ARP, DHCP, routing protocol discovery, and network management tasks.
Which OSI layer does this protocol belong to?
Broadcast addressing operates at the Network Layer (Layer 3) and also at the Data Link Layer (Layer 2) when using MAC-level broadcasts.
Is Broadcast Windows specific?
No, broadcast addressing is not Windows specific. It is a fundamental part of IPv4 networking and supported across all operating systems.
Is Broadcast Linux specific?
No, broadcast is not Linux specific. It is supported on all modern operating systems that implement standard networking stacks.
Which Transport Protocol is used by Broadcast?
Broadcast can use transport protocols like UDP. TCP does not support broadcasting because it requires a connection-oriented session.
Which Port is used by Broadcast?
Broadcast does not use a specific port. The port depends on the application (e.g., DHCP uses UDP ports 67 and 68).
Is Broadcast using client-server model?
Not necessarily. Broadcast is often used for service discovery and initial communication rather than a strict client-server model.
Can Broadcast addressing be used in IPv6?
No, IPv6 does not support broadcast addressing; it uses multicast and anycast instead.
What is a limited broadcast address?
The limited broadcast address (255.255.255.255) is used to communicate with all devices on the local network segment.
What is a directed broadcast address?
Directed broadcast targets all hosts on a specific subnet, such as 192.168.1.255 for the 192.168.1.0/24 subnet.
Does Broadcast increase network traffic?
Yes, broadcast traffic is sent to all devices in a subnet and can contribute to network congestion if excessive.
How do switches handle Broadcast traffic?
Switches forward broadcast frames out all ports except the incoming port, flooding the subnet.
Can Broadcast be filtered or controlled?
Yes, network devices can limit broadcast domains using VLANs and other segmentation techniques.
What protocols rely heavily on Broadcast?
Protocols like ARP, DHCP, NetBIOS, and routing protocol discovery use broadcast packets.
Is Broadcast reliable?
Broadcast uses connectionless protocols like UDP or Ethernet frames; reliability depends on the upper-layer protocols.
How does Broadcast differ from Multicast?
Broadcast targets all devices in a subnet, while multicast targets a specific group of subscribers.
Can Broadcast cause security risks?
Yes, broadcasts can be exploited for network reconnaissance and amplification attacks.
What is a broadcast storm?
A broadcast storm occurs when excessive broadcast traffic overwhelms network resources, causing congestion or outages.
How can Broadcast storms be prevented?
Using VLAN segmentation, storm control features on switches, and limiting unnecessary broadcast traffic helps prevent storms.
Is Broadcast supported in wireless networks?
Yes, but wireless networks handle broadcasts differently and may reduce efficiency due to shared medium access.
Can Broadcast be used for network discovery?
Yes, it is often used for discovering devices and services on local networks.
What are the drawbacks of Broadcast addressing?
Broadcast traffic can cause network congestion, security issues, and does not scale well in large networks.
Does Broadcast consume bandwidth?
Yes, since every device on the subnet receives broadcast packets, it can increase bandwidth consumption.
Is Broadcast address configurable?
The broadcast address is derived from the network address and subnet mask but can be manually set in some configurations.
How does Broadcast affect network performance?
Excessive broadcasts can degrade network performance by consuming resources on all devices within the broadcast domain.
In this section, you are going to learn
Terminology
Version Info
rfc details
Objective
Verify one-to-all communication on the subnet.
VM Configuration
# Enable broadcast replies on VM1 and VM2
test:~$ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=0
# Sender VM sends broadcast ping
test:~$ ping -b 192.168.1.255
WARNING: pinging broadcast address
PING 192.168.1.255 (192.168.1.255) 56(84) bytes of data.
64 bytes from 192.168.1.20: icmp_seq=1 ttl=64 time=1.48 ms
64 bytes from 192.168.1.10: icmp_seq=2 ttl=64 time=0.814 ms
64 bytes from 192.168.1.20: icmp_seq=2 ttl=64 time=0.932 ms
64 bytes from 192.168.1.10: icmp_seq=3 ttl=64 time=1.18 ms
64 bytes from 192.168.1.10: icmp_seq=4 ttl=64 time=1.11 ms
64 bytes from 192.168.1.10: icmp_seq=5 ttl=64 time=1.42 ms
64 bytes from 192.168.1.20: icmp_seq=5 ttl=64 time=1.42 ms
64 bytes from 192.168.1.20: icmp_seq=6 ttl=64 time=1.53 ms
64 bytes from 192.168.1.10: icmp_seq=6 ttl=64 time=1.53 ms
64 bytes from 192.168.1.10: icmp_seq=7 ttl=64 time=0.706 ms
64 bytes from 192.168.1.10: icmp_seq=7 ttl=64 time=0.939 ms
64 bytes from 192.168.1.20: icmp_seq=8 ttl=64 time=0.940 ms
64 bytes from 192.168.1.20: icmp_seq=9 ttl=64 time=1.27 ms
64 bytes from 192.168.1.10: icmp_seq=9 ttl=64 time=1.27 ms
64 bytes from 192.168.1.10: icmp_seq=10 ttl=64 time=0.825 ms
64 bytes from 192.168.1.20: icmp_seq=10 ttl=64 time=0.825 ms
64 bytes from 192.168.1.20: icmp_seq=11 ttl=64 time=0.516 ms
64 bytes from 192.168.1.10: icmp_seq=11 ttl=64 time=0.703 ms
64 bytes from 192.168.1.10: icmp_seq=12 ttl=64 time=0.932 ms
64 bytes from 192.168.1.20: icmp_seq=12 ttl=64 time=0.932 ms
64 bytes from 192.168.1.20: icmp_seq=13 ttl=64 time=1.13 ms
64 bytes from 192.168.1.10: icmp_seq=13 ttl=64 time=1.13 ms
64 bytes from 192.168.1.20: icmp_seq=14 ttl=64 time=9.04 ms
64 bytes from 192.168.1.10: icmp_seq=14 ttl=64 time=9.25 ms
^C
--- 192.168.1.255 ping statistics ---
14 packets transmitted, 14 received, +14 duplicates, 0% packet loss, time 13652ms
rtt min/avg/max/mdev = 0.516/1.654/9.249/2.095 ms
Capture Analysis
Wireshark shows ICMP packets received by both VM1 and VM2.
Destination IP is 192.168.1.255 (broadcast).
Observed duplicates are normal due to broadcast behavior.
Wireshark on Sender: Shows outgoing broadcast Echo Requests.
Note
Broadcast sends packets to all hosts in the subnet. Ensure icmp_echo_ignore_broadcasts is 0 to allow replies.
Wireshark Captures
packet details
usecases
Broadcast Support - Testcases
Broadcast Support - Test Cases
#
Test Case
Description
Expected Result
1
Send Limited Broadcast
Destination = 255.255.255.255
Packet delivered to all hosts on local network
2
Send Directed Broadcast
Destination = subnet broadcast (e.g., 192.168.1.255)
Packet delivered to all hosts in subnet
3
Send Broadcast with Valid Source
Source IP is valid
Packet accepted by receivers
4
Send Broadcast with Invalid Source
Source IP = 0.0.0.0
Packet dropped
5
Broadcast Packet with TTL = 1
TTL expires after one hop
Packet not forwarded
6
Broadcast Packet with TTL > 1
TTL > 1
Packet still not forwarded (broadcasts not routed)
7
Broadcast Packet with UDP
UDP datagram broadcasted
All hosts receive
8
Broadcast Packet with TCP
TCP not typically used
Packet dropped or ignored
9
Broadcast Packet with ICMP
ICMP Echo Request to broadcast
May be dropped by hosts
10
Broadcast Packet with ARP
ARP request broadcasted
All hosts on LAN receive
11
Broadcast Packet with DHCP Discover
DHCP Discover sent
All DHCP servers receive
12
Broadcast Packet with BOOTP
BOOTP request broadcasted
Server responds if available
13
Broadcast Packet with NetBIOS
NetBIOS name query broadcasted
All Windows hosts respond
14
Broadcast Packet with SNMP Trap
Trap sent to broadcast address
All SNMP listeners receive
15
Broadcast Packet with Custom App
App sends UDP broadcast
All listening clients receive
16
Broadcast Packet with VLAN
Broadcast scoped to VLAN
Only VLAN members receive
17
Broadcast Packet with Trunk Port
Tagged broadcast
Forwarded to correct VLANs
18
Broadcast Packet with Access Port
Untagged broadcast
Forwarded within VLAN
19
Broadcast Packet with ACL Permit
ACL allows broadcast
Packet forwarded
20
Broadcast Packet with ACL Deny
ACL blocks broadcast
Packet dropped
21
Broadcast Packet with Firewall
Firewall allows broadcast
Packet forwarded
22
Broadcast Packet Blocked by Firewall
Firewall blocks broadcast
Packet dropped
23
Broadcast Packet with NAT
NAT device receives broadcast
Packet not translated or forwarded
24
Broadcast Packet with Router
Router receives broadcast
Packet not forwarded to other networks
25
Broadcast Packet with Switch
Switch floods broadcast
All ports receive except source
26
Broadcast Packet with Hub
Hub repeats broadcast
All ports receive
27
Broadcast Packet with Wireless AP
Broadcast sent over Wi-Fi
All wireless clients receive
28
Broadcast Packet with VPN
Broadcast sent over VPN
May not be forwarded
29
Broadcast Packet with MPLS
MPLS network
Broadcast not supported
30
Broadcast Packet with IPv6
IPv6 used
Broadcast not supported (uses multicast)
31
Broadcast Packet with Logging Enabled
Logging active
Broadcast events logged
32
Broadcast Packet with Monitoring Tool
Tool captures broadcast
Packet visible in capture
33
Broadcast Packet with Packet Sniffer
Wireshark running
Broadcast packet captured
34
Broadcast Packet with Loopback Interface
Sent to 127.0.0.1
Packet not broadcasted
35
Broadcast Packet with Broadcast Storm
Excessive broadcasts
Network congestion occurs
36
Broadcast Packet with Rate Limiting
Broadcasts throttled
Excess packets dropped
37
Broadcast Packet with Storm Control
Switch limits broadcast rate
Excess packets dropped
38
Broadcast Packet with QoS
QoS policy applied
Broadcasts prioritized or limited
39
Broadcast Packet with Fragmentation
Large broadcast fragmented
Reassembled at receiver
40
Broadcast Packet with Invalid Checksum
Corrupted header
Packet dropped
41
Broadcast Packet with IP Options
Options present
Packet processed if supported
42
Broadcast Packet with Source Routing
Source route option
Packet dropped or ignored
43
Broadcast Packet with TTL = 0
TTL expired
Packet dropped immediately
44
Broadcast Packet with ICMP Redirect
Sent to broadcast
Packet dropped
45
Broadcast Packet with DHCP Relay
Relay agent forwards
Packet unicast to DHCP server
46
Broadcast Packet with Proxy ARP
Proxy responds
Host receives reply
47
Broadcast Packet with Duplicate IP Detection
ARP probe broadcasted
Conflict detected if IP in use
48
Broadcast Packet with Gratuitous ARP
ARP broadcasted without request
Used for IP conflict detection
49
Broadcast Packet with Wake-on-LAN
Magic packet broadcasted
Target device wakes up
50
Broadcast Packet with Legacy Protocol
NetBEUI or similar
Broadcast used for discovery
Reference links