Switching

Hi,

 

A costumer is having problem with broadcast in their network.

 

If server sends a broadcast packets to the switch, these packets are replicated to all switch ports including the one from where broadcast is originating.
In this way, traffic is duplicated on a port that is source of the broadcast.

For example:
If server broadcasts data by allocating 10% of port capacity
- Server network adapter is loaded with 20% (10% upstream to the switch, and 10% downstream)
- All other network adapters connected to switch will receive 10% of port capacity.

The problem really becomes visible only if the upstream traffic on port starts to approach 50% of port capacity, ie. the total traffic is 100%.

 

Is there any way to solve this problem in layer 2 switch?

 

 

I'm pretty sure you aren't supposed to see any broadcast traffic sent out the interface it was received on. If you are seeing this, I would contact jtac, as something is definitely wrong.

You can limit broadcast traffic using storm control under ethernet-switching-options.

set ethernet-switching-options storm-control interface ge-0/0/0 bandwidth 15000

Hi dscott,

 

Custumer had this problem on Cisco switch and planned to buy Juniper EX.  They plan to invest in Juniper, so they want to be sure that this problem doesn't exist on Juniper EX.

 

I've planned to set one EX2200 for testing, just to make sure.

I can't speak for how cisco handle this, but sending broadcast packets out on the same port they came in on is not how it should work.

 

From the JNCIS-ENT Switching study guide.

 

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. (If traffic originates on the switch, the switch floods that traffic out all interfaces.) When an unknown destination responds to traffic that has been flooded through a switch, the switch learns the MAC address of that node and updates its bridge table with the source MAC address and ingress port.

 

Also from the same study guide, Chapter 5 discusses handling traffic storms.

 

Storm control enables the switch to monitor traffic levels and to drop broadcast and unknown unicast packets when a specified traffic level—called the storm control level—is exceeded. By dropping packets that contribute to a traffic storm, a switch can prevent those packets from proliferating and degrading the LAN.

 

I would also like to suggest looking at an ex3200 rather than than the ex2200.  Take a look at the comparison of the switching features below.

 

http://www.juniper.net/techpubs/en_US/junos/topics/concept/ex-series-software-features-overview.html