DHCP Server and unnecessary traffic for your DHCP server.

Have you ever implemented central DHCP server for all of your network (VLANS), and you used a command "IP Helper-Address? The ip helper-address will actually forward many other UDP-based broadcasts to the address specified as tft, dns, time, netbios-ns, netbios-dgm, tacacs, bootpc, bootps etc. 

Many times it is generating unnecessary traffic for your DHCP server. Have you applied "ip forward-protocol udp ...." command to prevent this?

How to router prevent from ARP Strom?

 How to Router Prevent from ARP Strom?
Why some ARP entry will showing in ARP Table after respective time expires?


The extra time is the jitter added to each dynamic ARP entry when it is created. Random jitter is added to the ARP cache timeout in order to avoid synchronous expiration of the ARP entries, which might trigger an ARP storm. Jitter should be a random number between 0 seconds and 30 minutes, with a maximum jitter of 30 minutes.

Bursty Traffic Identification on Switch port

Traffic bursts can cause output drops even when the interface output rate is significantly lower than the maximum interface capacity. By default, the output rates in the show interface command are averaged over five minutes, which is not adequate to capture any short-lived bursts. It is best to average them over 30 seconds. In this case, you can use Wireshark in order to capture egress traffic with the Switched Port Analyzer (SPAN), which is analyzed in order to identify the bursts.

Cisco router load balancing and CEF (Cisco Express Forwarding)

#DoYouKnow #CiscoTips #Cisco

Per-destination or per-packet load-balancing depends on the type of switching scheme used for IP packets. By default, on most Cisco routers, fast switching is enabled under interfaces. This is a demand caching scheme that does per-destination load-balancing. To set per-packet load-balancing, enable process switching (or disable fast switching), use these commands:

Router(config-if)# no ip route-cache

Now the router CPU looks at every single packet and load balances on the number of routes in the routing table for the destination. This can crash a low-end router because the CPU must do all the processing.

Newer switching schemes such as Cisco Express Forwarding (CEF) allow you to do per-packet and per-destination load-balancing more quickly. However, it does imply that you have the extra resources to deal with maintaining CEF entries and adjacencies.

When you work with CEF, you could ask: Who does the load balancing, CEF or the routing protocol used? The way in which CEF works is that CEF does the switching of the packet based on the routing table which is being populated by the routing protocols.

I like cef...

#Extra tips for my blog readers:

, CEF performs the load-balancing once the routing protocol table is calculated.

Cisco Routers Ports (Cisco Study)

Cisco Routers Ports (Cisco Study)

You can read this post on http://deepuinfo.blogspot.com/p/cisco-study.html  on my blog

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Networking Devices (Cisco Study)

Networking Devices (Cisco Study)
You can Read on http://deepuinfo.blogspot.com/p/cisco-study.html Page on my Blog

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