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PLS-HELP no-mac-learning

‎11-29-2016 08:17 AM

Hello Guys, 

 

I need your help regarding no-mac-learning command

 

We'd faced an isssue in our link as as result tc/udp packets were transferred however ICMP pakcets were not getting transported.

 

We've vrf lite at customer side router .we checked with provider ( PTT ) they said issue was due to "no-mac-learning" was configured at their core switch

 

Now, If no-mac-learning is layer 2 command, it shud impact all the traffic (layer 3 traffic I mean ) , which it can only impacted ICMP traffic

 

Please share your views

2 REPLIES 2
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Re: PLS-HELP no-mac-learning

‎01-08-2017 05:22 AM

Hi,

 

You are correct this seems not the reason for ICMP packet drops. However, you can apply the ICMP filter as given in below KB to check/troubleshoot the ICMP packet drop.

 

 

Example Firewall Filter used to count the number of incoming packets

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Re: PLS-HELP no-mac-learning

‎01-08-2017 07:43 PM

Hi Folks,

When a L2 switch is initially connected to an Ethernet LAN, it has no information about the devices connected to the network. Learning is a process the switch uses to obtain the MAC addresses of nodes on the network. The switch stores all learned MAC address in the bridge table. To learn MAC addresses, the switch examines the Ethernet header information of all received frames from the LAN, looking for source MAC addresses of sending nodes. The switch places learned MAC addresses into its bridge table, along with two other pieces of information—the interface (or port) on which the traffic was received and the time when the MAC address was learned. The port information is used to forward traffic to its intended destination (forwarding mechanism) while the timestamp information is used
to keep the bridge table up-to-date (aging mechanism). We discuss the forwarding and aging mechanisms in detail on subsequent pages in this section.

 

To disable MAC learning follows:
Switch# set ethernet-switching-options interfaces ge-1/1/1.0 no-mac-learning

 

Flooding is a transparent mechanism used to deliver packets to unknown MAC addresses. If the bridging table has
no entry for a particular destination MAC address or if the packet received is a broadcast or multicast packet, the
switch floods the traffic out all interfaces except the interface on which it was received.

 

I dont find any specifc reason for only ICMP packets are dropped and not udp/tcp. Is the ICMP tarffic is to the same destination as udp/tcp?

-Python JNCIE 3X [SP|DC|ENT] JNCIP-SEC JNCDS 3X [ WAN | DC|SEC] JNCIS-Cloud JNCIS-DevOps CCIP ITIL
#Please mark my solution as accepted if it helped, Kudos are appreciated as well.
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