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Cisco loopback traffic?

Hi,

I have on a catalyst 2900 this config :

interface FastEthernet0/1

switchport access vlan 600

switchport trunk native vlan 600

switchport trunk allowed vlan none

switchport mode access

switchport nonegotiate

switchport block multicast

switchport block unicast

switchport port-security

switchport port-security aging time 10

switchport port-security aging type inactivity

switchport port-security mac-address sticky

no cdp enable

spanning-tree portfast

spanning-tree bpdufilter enable

spanning-tree bpduguard enable

spanning-tree guard root

on that port I have a linux box that get this arp traffic:

# tethereal

Capturing on eth0

0.000000 Cisco_53:78:83 -> Cisco_53:78:83 LOOP Reply

9.998184 Cisco_53:78:83 -> Cisco_53:78:83 LOOP Reply

# tcpdump -i eth0 -n

tcpdump: listening on eth0

00:58:15.592672 0:14:1c:53:78:83 0:14:1c:53:78:83 loopback 60:

0000 0100 0000 0000 0000 0000 0000 0000

0000 0000 0000 0000 0000 0000 0000 0000

0000 0000 0000 0000 0000 0000 0000

This is something I should worry about? In case the answer is yes, how should I block this kind of traffic?

Tahnkx in advance

1 ACCEPTED SOLUTION

Accepted Solutions
VIP Purple

Re: Cisco loopback traffic?

Hello Luis,

I think what you are looking at are Ethertype 0x9000 frames, which basically are loopback frames sent to the MAC address of the FastEthernet0/1 interface, and which are used to test if the link is ok (those frames are also called ´Enet Config Test´). I am not sure how to turn them off, can you try:

interface FastEthernet0/1

-->no keepalive

?

Regards,

GP

1 REPLY
VIP Purple

Re: Cisco loopback traffic?

Hello Luis,

I think what you are looking at are Ethertype 0x9000 frames, which basically are loopback frames sent to the MAC address of the FastEthernet0/1 interface, and which are used to test if the link is ok (those frames are also called ´Enet Config Test´). I am not sure how to turn them off, can you try:

interface FastEthernet0/1

-->no keepalive

?

Regards,

GP

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