Month: May 2013

Static floating route is static route like any other but with added administrative distance in the configuration

R1(config)#ip route 172.16.10.0 255.255.255.0 10.10.10.2 200

Static Floating Routes are very interesting so I decided to give you a short description and an example.

A static floating route is the same as normal static route except that this kind of static route has administrative distance configured to some value higher than 1.

Remember that if we configure normal static route like this:

R1(config)#ip route 172.16.10.0 255.255.255.0 10.10.10.2

It will send all packets destined for 172.16.10.0/24 network to the neighbour with interface address 10.10.10.2

Of course, this static route will have administrative distance (AD) of 1 by default.

If we make the configuration like this:

R1(config)#ip route 172.16.10.0 255.255.255.0 Serial 0/0

In this case, the AD will be zero (0). Pretty cool right? There’s another article about that here.

In either case, this is normal because this is the way we configure routing on our router or if we use a dynamic routing protocol, this is then the way of overriding routing protocol decisions for some exceptions.

But what if we want to use a static route to make something completely opposite?

If we want to use static route only to be a backup route. Then we will need to give the precedence to the path learned by some IGP (Interior Gateway Protocol) like OSPF for example. We know that most paths (routes) learned by OSPF protocol have Administrative Distance of 110. In that case, the Administrative distance of a static route needs to be bigger than 110 if we don’t want to kick out the OSPF route from routing table.

If you know what delay is, jitter is simply the difference in packet delay. In other words, jitter is measuring the time difference in packet inter-arrival time.

It is a specific phenomenon that normally exists in bigger packet-switched networks. As a time-shift phenomenon, it usually does not cause any communication problems. Actually, TCP/IP is responsible for dealing with the jitter impact on communication.

On the other hand, when we speak about Voice traffic and VoIP network environment this can be an issue. When someone is sending VoIP communication at a normal interval, (let’s say one frame every 10 ms), those packets could have stuck somewhere in-between the network and not arrive at expected regular pace to the destined station. It is not usual, but the packets could take different routes or get load-balanced through two similar paths where one of those is congested in that moment.

That’s the whole jitter phenomenon. We can look at it as the anomaly in tempo, with which packet is expected to come and the time he was late to really get there.

In the image above, you can notice that the time it takes for packets to be sent is not the same as the time in which they will arrive at the receiver side. One of the packets encounters some delay on its way and it is received a little later than it was expected. Jitter buffers are entering the story. They will try to remedy packet delay if required and if possible. VoIP packets in networks have very changeable packet inter-arrival intervals because they are usually smaller than normal data packets, and are therefore more numerous, with a bigger chance to get some delay.