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Ahmed M Alzaeem
Beginner

how the MLS behave in this case ?

hi ,

i want to ask about behaviour of MLS .

my case is if a packet reached a MLS and niether  destination mac nor destination route in the L3 fib table are exist .

what is the behavior here ? will the MLS  consider him self a switch and flood the frame to all interfaces except the recived one ??

or

the MLS consider him self a router and send this packet to the default route???

what will happen if there is no default route in the FIB table of MLS ??

regards

3 REPLIES 3
Raju Sekharan
Cisco Employee

When an L3 switch receives a packet, it will 1st look at the destination MAC. If the destination MAC is of the L3 Switch, then it goes to L3 processing. In L3 level, it examins the detination IP, if the destination route is present in routing table, it will route the packet.

Question

1. my case is if a packet reached a MLS and niether  destination mac nor destination route in the L3 fib table are exist .

Answer:

If thie packet is arrived on a L2 port, it will flood the packet on all the ports belonging to that VLAN and trunks allowing that VLAN. it won't look at FIBB table becasue the destination MAC doesn't belong to that Switch

If the traffic is coming on an L3 port, the L3 switch will drop if the destination MAC ( unicsat mac-address) is not of that interface.

Thanks

Raju

hi ,

thanks for reply ,

but how the MLS  know if the desination mac belongs to L3 sw or another L2 sw ?

Hi

CAM table.

Switch  will be aware of it's own mac-addresses. If you look at the show mac-address table you can see the MAC's assigned to the switch, dynamically learned MACs and statically configured MACs

When an L2 packet comes to switch, it will look at the CAM table corresponding to the access VLAN of that port.

If the destination MAC is not present in the CAM table, switch will flood that packet in that VLAN

Thank you

Raju