Traffic Storm control

[estelamathew]

Hello Dears,

What one can suggest a percentage value for traffic storm-control for Broadcast and Unicast traffic on Catalyst 3550 Access switches (END USERS) Ports.

Thanks,

[Giuseppe Larosa]

Hello Estela,

on GE ports on C4500 we use 1% with  /24 IP subnets with no problem

suggested value depends from:

IP subnet size, the bigger the IP subnet the higher level or broadcast is present on the vlan

port speed

if you use /24 IP subnets you can start by using 10% and you should be fine on FE ports (100 Mbps). You could also try 5%

Hope to help

Giuseppe

[estelamathew]

Thanks Giuseppe,

As u have suggested a 10% of rising threshold and i imagine 8% for falling threshold, But i want to know if My subnet is /24 and if suppose when a destination is not known buy the switch the switch will do broadcast so the above threshold should not affect the genuine broadcast for the user traffic.

Thanks,

[Giuseppe Larosa]

Hello Estela,

I would suggest to use the same threshold values for limiting unknown unicast flooding in normal conditions the unicast flooding should be limited.

Even in a long file transfer that is TCP based the receiving side has to send TCP ACKs back to sender so it should be able to be present in the switch CAM table.

From an old configuration guide for C3550 note:

a) When storm control is enabled, the switch monitors packets passing from an interface to the switching

bus and determines if the packet is unicast, multicast, or broadcast. The switch monitors the number of

broadcast, multicast, or unicast packets received within the 1-second time interval, and when a threshold

for one type of traffic is reached, that type of traffic is dropped. This threshold is specified as a

percentage of total available bandwidth that can be used by broadcast (multicast or unicast) traffic.

b) When the rate of multicast traffic exceeds a set threshold, all incoming traffic (broadcast, multicast, and

unicast) is dropped until the level drops below the threshold level. Only spanning-tree packets are

forwarded. When broadcast and unicast thresholds are exceeded, traffic is blocked for only the type of

traffic that exceeded the threshold.

this was 12.1(19)EA1

last IOS for C3550 is 12.2(44)SE:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.2_44_se/configuration/guide/swtrafc.html#wp1242514

Storm control uses one of these methods to measure traffic activity:

•Bandwidth as a percentage of the total available bandwidth of the port that can be used by the broadcast, multicast, or unicast traffic

•Traffic rate in packets per second at which broadcast, multicast, or unicast packets are received (Cisco IOS Release 12.1(22)EA1 or later)

>> However, because of hardware limitations and the way in which packets of different sizes are counted, threshold percentages are approximations. Depending on the sizes of the packets making up the incoming traffic, the actual enforced threshold might differ from the configured level by several percentage points.

Hope to help

Giuseppe

[estelamathew]

Hello Giuseppe,

My access switches are terminating on CORE 6500 instead of applying storm control on access ports if i apply on trunk ports on CORE???

I have read the 3550 user guide storm-control chapter how to calculate the values to be applied on port,as such in ur previos mail u told me according to how big the subnet is. so are there any other tricks to calculate the storm control.

What storm-control we should implement on 6500 Core switches on tunk ports??

Thanks

[Giuseppe Larosa]

Hello Estela,

it is not the same limiting on the core on uplinks ma be too late.

Storm control is of help during bridging storms caused by loops that can form in a campus.

It can help to give you a chance to remotely access the network devices.

So I recommend  to deploy it on the access layer too.

You can use for unknown unicast traffic bigger values if you like with no problem

Hope to help

Giuseppe

[estelamathew]

Hello Giuseppe,

I want to know the formula OR on what basis we should limit storm control for Bradcast,unicast and multicast.

Thanks