Switch and mac address table
I thought that a switch learnt the mac addresses by the computers sending out packets. However when I configured 2 switches, and 2 pc's, 1 pc connected to 1 switch, the other pc connected to the other switch, and then both switches connected to each other, there were mac addresses in the mac address table without there being any packets being sent. Why/How does this happen?
switch mac-address
asked 16 hours ago
The_BearThe_Bear
433
|
show 2 more comments
I thought that a switch learnt the mac addresses by the computers sending out packets. However when I configured 2 switches, and 2 pc's, 1 pc connected to 1 switch, the other pc connected to the other switch, and then both switches connected to each other, there were mac addresses in the mac address table without there being any packets being sent. Why/How does this happen?
switch mac-address
asked 16 hours ago
The_BearThe_Bear
433
4
PCs are actually pretty chatty. They do a lot of things in the background.
– Ron Trunk
16 hours ago
1
Are you sure there were no packet sent? How? Modern OSes have a lot of background network activity. This can also be due to gratuitous ARP. See this answer for example
– JFL
16 hours ago
Definitely no packets sent when it was first viewed, packets were sent afterwards and the table was view again.
– The_Bear
16 hours ago
4
Then you have magic switches.
– JFL
15 hours ago
6
Clearly the PCs sent frames. That’s how the switch learned the MACs.
– Ron Trunk
15 hours ago
|
show 2 more comments
I thought that a switch learnt the mac addresses by the computers sending out packets. However when I configured 2 switches, and 2 pc's, 1 pc connected to 1 switch, the other pc connected to the other switch, and then both switches connected to each other, there were mac addresses in the mac address table without there being any packets being sent. Why/How does this happen?
switch mac-address
asked 16 hours ago
The_BearThe_Bear
433
I thought that a switch learnt the mac addresses by the computers sending out packets. However when I configured 2 switches, and 2 pc's, 1 pc connected to 1 switch, the other pc connected to the other switch, and then both switches connected to each other, there were mac addresses in the mac address table without there being any packets being sent. Why/How does this happen?
switch mac-address
switch mac-address
asked 16 hours ago
The_BearThe_Bear
433
asked 16 hours ago
The_BearThe_Bear
433
asked 16 hours ago
The_BearThe_Bear
433
asked 16 hours ago
The_BearThe_Bear
433
asked 16 hours ago
The_BearThe_Bear
433
433
4
PCs are actually pretty chatty. They do a lot of things in the background.
– Ron Trunk
16 hours ago
1
Are you sure there were no packet sent? How? Modern OSes have a lot of background network activity. This can also be due to gratuitous ARP. See this answer for example
– JFL
16 hours ago
Definitely no packets sent when it was first viewed, packets were sent afterwards and the table was view again.
– The_Bear
16 hours ago
4
Then you have magic switches.
– JFL
15 hours ago
6
Clearly the PCs sent frames. That’s how the switch learned the MACs.
– Ron Trunk
15 hours ago
|
show 2 more comments
4
PCs are actually pretty chatty. They do a lot of things in the background.
– Ron Trunk
16 hours ago
1
Are you sure there were no packet sent? How? Modern OSes have a lot of background network activity. This can also be due to gratuitous ARP. See this answer for example
– JFL
16 hours ago
Definitely no packets sent when it was first viewed, packets were sent afterwards and the table was view again.
– The_Bear
16 hours ago
4
Then you have magic switches.
– JFL
15 hours ago
6
Clearly the PCs sent frames. That’s how the switch learned the MACs.
– Ron Trunk
15 hours ago
4
4
PCs are actually pretty chatty. They do a lot of things in the background.
– Ron Trunk
16 hours ago
PCs are actually pretty chatty. They do a lot of things in the background.
– Ron Trunk
16 hours ago
1
1
Are you sure there were no packet sent? How? Modern OSes have a lot of background network activity. This can also be due to gratuitous ARP. See this answer for example
– JFL
16 hours ago
Are you sure there were no packet sent? How? Modern OSes have a lot of background network activity. This can also be due to gratuitous ARP. See this answer for example
– JFL
16 hours ago
Definitely no packets sent when it was first viewed, packets were sent afterwards and the table was view again.
– The_Bear
16 hours ago
Definitely no packets sent when it was first viewed, packets were sent afterwards and the table was view again.
– The_Bear
16 hours ago
4
4
Then you have magic switches.
– JFL
15 hours ago
Then you have magic switches.
– JFL
15 hours ago
6
6
Clearly the PCs sent frames. That’s how the switch learned the MACs.
– Ron Trunk
15 hours ago
Clearly the PCs sent frames. That’s how the switch learned the MACs.
– Ron Trunk
15 hours ago
|
show 2 more comments
3 Answers
3
active
oldest
votes
When you connect a PC to a network switch ("link up"), the PC performs at least one of these procedures:
- (most commonly) request an IP address lease from a DHCP server
- (when DHCP fails or is deactivated) automatically configure a link-local IP address (aka zero-config or APIPA)
- (when a static IP address is configured) send an ARP probe to detect an address collision
All of these methods send out broadcast frames from the PC which populate the MAC table in all the switches in the network (broadcast domain / VLAN).
answered 15 hours ago
Zac67Zac67
29.4k21859
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
add a comment |
PCs have many background tasks that send data all the time, even when you’re “not doing anything.” These frames will populate the MAC table.
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
add a comment |
You might think no packets have been sent, but Computers do a lot of talking in the background, given all the services functioning in the background.
edited 10 hours ago
Cown
6,26231030
answered 11 hours ago
PantheraPanthera
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
protected by Ron Maupin♦ 7 hours ago
Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
Would you like to answer one of these unanswered questions instead?
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
When you connect a PC to a network switch ("link up"), the PC performs at least one of these procedures:
- (most commonly) request an IP address lease from a DHCP server
- (when DHCP fails or is deactivated) automatically configure a link-local IP address (aka zero-config or APIPA)
- (when a static IP address is configured) send an ARP probe to detect an address collision
All of these methods send out broadcast frames from the PC which populate the MAC table in all the switches in the network (broadcast domain / VLAN).
answered 15 hours ago
Zac67Zac67
29.4k21859
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
add a comment |
When you connect a PC to a network switch ("link up"), the PC performs at least one of these procedures:
- (most commonly) request an IP address lease from a DHCP server
- (when DHCP fails or is deactivated) automatically configure a link-local IP address (aka zero-config or APIPA)
- (when a static IP address is configured) send an ARP probe to detect an address collision
All of these methods send out broadcast frames from the PC which populate the MAC table in all the switches in the network (broadcast domain / VLAN).
answered 15 hours ago
Zac67Zac67
29.4k21859
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
add a comment |
When you connect a PC to a network switch ("link up"), the PC performs at least one of these procedures:
- (most commonly) request an IP address lease from a DHCP server
- (when DHCP fails or is deactivated) automatically configure a link-local IP address (aka zero-config or APIPA)
- (when a static IP address is configured) send an ARP probe to detect an address collision
All of these methods send out broadcast frames from the PC which populate the MAC table in all the switches in the network (broadcast domain / VLAN).
answered 15 hours ago
Zac67Zac67
29.4k21859
When you connect a PC to a network switch ("link up"), the PC performs at least one of these procedures:
- (most commonly) request an IP address lease from a DHCP server
- (when DHCP fails or is deactivated) automatically configure a link-local IP address (aka zero-config or APIPA)
- (when a static IP address is configured) send an ARP probe to detect an address collision
All of these methods send out broadcast frames from the PC which populate the MAC table in all the switches in the network (broadcast domain / VLAN).
answered 15 hours ago
Zac67Zac67
29.4k21859
answered 15 hours ago
Zac67Zac67
29.4k21859
answered 15 hours ago
Zac67Zac67
29.4k21859
answered 15 hours ago
Zac67Zac67
29.4k21859
29.4k21859
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
add a comment |
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
Also, gratuitous ARP, as mentioned in the comments to the question.
– Jörg W Mittag
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
And an ARP for the default gateway and DNS servers if defined either locally or by DHCP plus UPNP discovery, etc.
– grahamj42
8 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
Strictly speaking this depend on OS and network configuration. If you were to disable IPv4 none of the packets you mention would be sent. For another example look at IPv6, it doesn't use broadcast only multicast. There are switches which will treat them the same, but a switch does not have to forward multicast packets onto all ports.
– kasperd
6 hours ago
add a comment |
PCs have many background tasks that send data all the time, even when you’re “not doing anything.” These frames will populate the MAC table.
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
add a comment |
PCs have many background tasks that send data all the time, even when you’re “not doing anything.” These frames will populate the MAC table.
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
add a comment |
PCs have many background tasks that send data all the time, even when you’re “not doing anything.” These frames will populate the MAC table.
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
PCs have many background tasks that send data all the time, even when you’re “not doing anything.” These frames will populate the MAC table.
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
answered 15 hours ago
Ron TrunkRon Trunk
36.6k33374
36.6k33374
add a comment |
add a comment |
You might think no packets have been sent, but Computers do a lot of talking in the background, given all the services functioning in the background.
edited 10 hours ago
Cown
6,26231030
answered 11 hours ago
PantheraPanthera
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
You might think no packets have been sent, but Computers do a lot of talking in the background, given all the services functioning in the background.
edited 10 hours ago
Cown
6,26231030
answered 11 hours ago
PantheraPanthera
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
You might think no packets have been sent, but Computers do a lot of talking in the background, given all the services functioning in the background.
edited 10 hours ago
Cown
6,26231030
answered 11 hours ago
PantheraPanthera
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
You might think no packets have been sent, but Computers do a lot of talking in the background, given all the services functioning in the background.
edited 10 hours ago
Cown
6,26231030
answered 11 hours ago
PantheraPanthera
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 10 hours ago
Cown
6,26231030
edited 10 hours ago
Cown
6,26231030
edited 10 hours ago
Cown
6,26231030
6,26231030
answered 11 hours ago
PantheraPanthera
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 11 hours ago
PantheraPanthera
1
answered 11 hours ago
PantheraPanthera
1
1
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Panthera is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
protected by Ron Maupin♦ 7 hours ago
Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
Would you like to answer one of these unanswered questions instead?
4
PCs are actually pretty chatty. They do a lot of things in the background.
– Ron Trunk
16 hours ago
1
Are you sure there were no packet sent? How? Modern OSes have a lot of background network activity. This can also be due to gratuitous ARP. See this answer for example
– JFL
16 hours ago
Definitely no packets sent when it was first viewed, packets were sent afterwards and the table was view again.
– The_Bear
16 hours ago
4
Then you have magic switches.
– JFL
15 hours ago
6
Clearly the PCs sent frames. That’s how the switch learned the MACs.
– Ron Trunk
15 hours ago