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why two switches which co...

why two switches which connect to the other with different vlans can communicate with each other?

Created: Apr 22, 2019 02:40:57Latest reply: Aug 13, 2021 16:14:31 1008 12 1 0 0
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we got two switches, both are s5720HI, and when connected these two switches with interface which belongs to the different vlans, why they can communicate with each other successful. Shouldn't it be impossible to communication because of the connected interface are in different vlans?

topology as below shows:

104046s0uzr2i825r4it1z.png?switch_connec

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chenhui
Admin Created Apr 22, 2019 03:05:10

Good day sir @sim_157!

As you said, LSW1 and LSW2 connect to each other via the access port, so they can communicate with each other, because when the packets are forwarded outside the access port, they will not be tagged. 

So when the interface is configured as the access port, the switch will transfer the packets which are untagged, no matter which device sends this packet out.
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nochhie
nochhie Created Aug 4, 2021 04:29:27 (0) (0)
 
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chenhui
chenhui Admin Created Apr 22, 2019 03:05:10

Good day sir @sim_157!

As you said, LSW1 and LSW2 connect to each other via the access port, so they can communicate with each other, because when the packets are forwarded outside the access port, they will not be tagged. 

So when the interface is configured as the access port, the switch will transfer the packets which are untagged, no matter which device sends this packet out.
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nochhie
nochhie Created Aug 4, 2021 04:29:27 (0) (0)
 
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sim_157
sim_157 Created Apr 22, 2019 03:09:25

Posted by chenhui at 2019-04-22 03:05 @sim_157good day sir, as you said, the LSW1 and LSW2 connects to each other with access port, so the ...
thanks for your support,
you mean switch will accept all the untagged packets no matter whether they comes from the PC or other switch?
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nochhie
nochhie Created Aug 4, 2021 04:29:32 (0) (0)
 
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chenhui
chenhui Admin Created Apr 22, 2019 03:11:54

Posted by sim_157 at 2019-04-22 03:09 thanks for your support,you mean switch will accept all the untagged packets no matter whether the ...
yes, the switch will accept all the untagged packets, though the remote device is another switch which configured the connected interface another vlan.
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chenhui
chenhui Admin Created Apr 22, 2019 03:14:05

Posted by sim_157 at 2019-04-22 03:09 thanks for your support,you mean switch will accept all the untagged packets no matter whether the ...
by the way, switch is just a machine, it is not so intelligent, it cannot recognize which type of device it connected with.
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Hobbit
Hobbit Created Apr 22, 2019 03:21:28

Very useful
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bigwangz
bigwangz Created Apr 29, 2019 01:39:57

My friend
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IndianKid
IndianKid Moderator Author Created May 21, 2021 12:13:05

Hi Sim,

is each Switch VLAN Interface having the IP assigned? if yes what is both VLAN Swicthinterface IP? did you configure any routing on switch or firewall or router connected to it.?

Example in your case: one switch is having a VLAN ID 10(untagged VLAN 10) to access port and another switch is having a VLAN ID 100 Access port(untagged VLAN 100).
When you connect a cable between these two ports, you will have communication because the first switch and second swicth acting as layer 2 with untagged packets. but if you configure the different network for both interfaces it won't communicate.
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Unicef
Unicef MVE Created Jul 7, 2021 07:45:12

Good answer
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nochhie
nochhie Created Aug 4, 2021 04:29:39

why two switches which connect to the other with different vlans can communicate with each other?-4069329-1
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