CODEWITHSUNDEEP
linuxnetwork-programming
Chinaxing
Chinaxing

Reputation: 8884

why i can not disable multicast request

I use the following command to disable the eth0 interface's multicast mode , but i not works :

sudo ifconfig eth0 -multicast

when do this, the eth0's configure is so:

ifconfig -v eth0 

eth0    Link encap:Ethernet  HWaddr 00:16:3E:E8:43:01  
          inet addr:10.232.67.1  Bcast:10.232.67.255  Mask:255.255.255.0
          UP BROADCAST RUNNING  MTU:1500  Metric:1
          RX packets:46728751 errors:0 dropped:0 overruns:0 frame:0
          TX packets:15981372 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:8005709841 (7.4 GiB)  TX bytes:3372203819 (3.1 GiB)

then, i do icmp echo_request in host 10.232.67.2:

ping 224.0.0.1

and tcpdump the package on host 10.232.67.1:

tcpdump -i eth0 host 224.0.0.1 -n

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
21:11:03.182813 IP 10.232.67.2 > 224.0.0.1: ICMP echo request, id 3639, seq 324, length 64
21:11:04.184667 IP 10.232.67.2 > 224.0.0.1: ICMP echo request, id 3639, seq 325, length 64
21:11:05.186781 IP 10.232.67.2 > 224.0.0.1: ICMP echo request, id 3639, seq 326, length 64

so, how to disable the multicast mode ?

by the way , when i disable the broadcast:

sudo ifconfig eth0 -broadcast

error message is :

Warning: Interface eth0 still in BROADCAST mode.

so, why can't stop broad cast mode ?

Upvotes: 2

Views: 10509

Answers (1)

Shawn Balestracci
Shawn Balestracci

Reputation: 7540

To disable multicast on an interface (you had it right):

ifconfig eth0 -multicast

tcpdump without the -p flag puts the interface in PROMISCUOUS mode, so it captures any traffic on the wire. If you're on a hub, you can see traffic sent to/from everyone else. When an interface isn't in promiscuous mode, it ignores all traffic not sent to it. If you try the tcpdump and ping without promiscuous mode, and multicast disabled, you shouldn't see the traffic:

tcpdump -p -i eth0 host 224.0.0.1 -n

You don't want to disable BROADCAST mode. It just designates the broadcast address for your subnet.

Upvotes: 4

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