C6509 switch send unicat as broadcast

Answered Question
Nov 11th, 2009

hi,

In our company C6509, running s72033-ipservices_wan-mz-122-33.SXH4, i found some times it might send normal unicast

traffic as broadcast. like host A send unicast to host B and third host C on the same VLAN may receive this traffic.

and it's intermittent.

any help will be appreciated.

joe

I have this problem too.
0 votes
Correct Answer by wandering_997 about 7 years 2 months ago

( I'll post topology in next reply )

Picture PC-1 pings PC-2.

When MAC address of PC-2 expires on 6509-B, but there's still a PC-2's entry in the ARP table of 6509-A.

6509-A (1.1.1.1) routes all ICMP packets from PC-1 to 6509-B (2.2.2.1), and the ICMP packets are broadcasted as there's no MAC entry of 2.2.2.20 in the mac-address-table of 6509-B.

---- Solution ----

A. Change mac aging-time same to ARP aging-time on both 6509.

B. Make mac unexpired on both 6509.

I choosed solution B and it worked.

Dayong

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wandering_997 Wed, 11/11/2009 - 18:07

Hi Joe,

Try to check the mac address table, especially the mac address which is the source mac of broadcast.

And, how many 6509 do you have? Do you use HSRP with STP to split the traffic in a redundant network?

I have been experienced a unicast broadcast issue, there're right arp table entries at the active hsrp switch, but there's no mac address in the mac-address-table of the standby hsrp switch.

HTH

Wandering

joecb_sg497 Wed, 11/11/2009 - 19:49

hi DAYONG,

yes, we have two C6509 with HSRP enabled;

i saw two such cases, one case is a host send packet to another host but routing via the HSRP gateway hosting on C6509, even through i think C6509 should know this MAC but it still broadcast it out.

like to know how your issue had been solved.

joe

Correct Answer
wandering_997 Wed, 11/11/2009 - 22:21

( I'll post topology in next reply )

Picture PC-1 pings PC-2.

When MAC address of PC-2 expires on 6509-B, but there's still a PC-2's entry in the ARP table of 6509-A.

6509-A (1.1.1.1) routes all ICMP packets from PC-1 to 6509-B (2.2.2.1), and the ICMP packets are broadcasted as there's no MAC entry of 2.2.2.20 in the mac-address-table of 6509-B.

---- Solution ----

A. Change mac aging-time same to ARP aging-time on both 6509.

B. Make mac unexpired on both 6509.

I choosed solution B and it worked.

Dayong

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