Swich table in case of CRC error

Question

I'm really confused about how the basic idea of updating the switch table works. In the case that the CRC is wrong it still updates the SMAC to use it next time maybe? Maybe because the error could be there (SMAC) the switch drops the SMAC with the message?

Another thing is what happened first, update the table or first send the message in case of store&forward mode?

Answer 1

first look at this picture

The Scenario is PC1 10.0.0.2 try to Ping PC3 10.0.0.4 :

1. PC1 Send ARP Message (BroadCast) Message and the switch is one broadcast domain it mean it will receive broadcast msg then send all messages to any device connected to it on all interfaces it will send message to PC2 then PC3 ok then ask who is 10.0.0.4 then the PC3 will answer then send the answer again to the switch and say thats me how this happen ?

Note: You Can See These Messages on Wireshark

ARP Message (Broadcast) contains : SIP (Source IP) | DIP (Destination IP) | SMAC(Source Mac) | FF:FF:FF:FF:FF:FF (Destination MAC ~> BroadCast Message) .

ok how the PC3 Answer ?

the ARP Protocol will Answer then send SMAC (11:11:11:11:11:11) | DMAC (33:33:33:33:33:33)

so now the Switch will Save both of them in CAM TABLE Like this picture :

ok how the frame sent .. it based on the Frame Check Sequence (FCS) its an extra detecting code in a communications protocol Frames are used to send upper-layer data and ultimately the application data from a source to a destination but the detection doen't mean error recovery just define the errored frame then discared it because ethernet takes no action to be retransmitted so FSC field contains a number that calculated by the source node based on the data in the frame this number added to the end of a frame that is sent when the destination node receives the frame the FCS number is recalculated and compared with the FCS number which included in the frame if the two numbers are different an error occurred and the frame will be discard with sending host computing the CRC on the entire frame and append this trailer like tagging it to the data then the receiving host recomputes the CRC on the frame then compares it to the received FCS in this case it can detect any data lost or altered i n transit so it will not be necessary to update the CAM TABLE because it will not accept any frame that corrupted you can clear or flush CAM TABLE via clear mac address-table dynamic or static please read more about FCS and CRC and how the frame sending the message https://en.wikipedia.org/wiki/Frame_check_sequence

UPDATED

what if the brodcast not reply ?the switch save the SMAC?

let me show you a practical example first go and show the CAM TABLE its empty

ok what if PC1 try to ping non-existent ip address for example 10.0.0.5

ok Check Now the CAM TABLE again

the switch storing just the SMAC

Ok Again go and ping pc3 now it will replay

now check the CAM TABLE again

ok what if you want to flush your CAM TABLE try clear mac-address-table dynamic or static