Month: May 2013

What is static floating route

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 routeDefining the packets route using Static Floating Routes is very interesting topic so I decided to give you a short description of Static floating routes with an example. Static floating route is the same as normal static route except that this kind of static route has Administrative distance configured to some other value 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 neighbor with interface address 10.10.10.2 and of course that 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? I didn’t know that difference for a long time but there is another article in the process of writing that explains why that is so.

In either cases of course, this would be normal because almost every time we configure the static route to override some routing protocol decision. 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 to some subnet 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 some static route needs to be bigger than 110 if we don’t want to kick out the OSPF route from routing table.

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What is Jitter in Networking?

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

jitter

In this image above, you can notice that the time it takes for packets to be send is not the same as the time in which he will arrive at the receiver side. One of the packets encounters some delay on his way and it is received 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 bigger chance to get some delay.

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