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Making Sense of Broadband networks: PPPoE Explained

A bit of background First .. PPPoE stands for Point to Point over Ethernet and is the successor of PPPoA. PPPoE is simply a method of encapsulating PPP packets into Ethernet frames. The standard is defined in RFC2516 . IPoE is growing very quickly but as far as I can tell PPPoE is still very widely deployed model in broadband networks. PPP protocol is a very mature protocol that was originally implemented to create and maintain direct connections between two nodes. PPP is such a protocol that provides many features but the one that is most interesting to broadband providers is the ability …

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PPPoE MTU Explained

PPPoE MTU is a buzz word that many people ask about even if they don’t have anything to do with network engineering. Just being a broadband subscriber with a PPPoE circuit is enough to get introduced to the concept. In this post I will be explaining how PPPoE MTU is calculated and what is the default value. Therefore I would expect the reader to be familiar with what MTU is and with What PPPoE is. PPPoE MTU: PPPoE MTU defines the maximum number of bytes that a PPPoE payload can have. This typically starts from IP layer in most cases. …

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Making sense of Broadband networks – Part 1

Broadband is a hot topic in the telecommunications industry nowadays; it is becoming the bread and butter for so many service providers and mobile carriers with the big growth and penetration rates in these technologies in the recent years.  ( Check this report about the EOCD countries). Although it is that important, broadband topics probably are not covered in any certification/education track and the reason might be that there is no “one shop suits all” in this field as in routing and switching technologies. In this post and others my aim is to provide some engineers with a brief but useful …

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Static routes and next hops

Today I have received a question by mail from one of our readers asking about the difference between pointing the static route to a next hop address or pointing it to the exit interface itself as shown in the example below: !-- Pointing to next hop address ip route !-- or Pointing to the interface ip route s1/0 Although it seems to be an easy question to answer but I it was a little bit hard for me to write the answer in words. You know, sometimes we know things but when time comes for …

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Frame-relay Discard Eligibility Bit (DE)

What is the DE bit ? The DE bit is used to indicate that the frame has a lower importance than other frames and should be dropped first if the network experienced congestion. How to set the DE bit? We can use a simple network to test our configuration. R1 is connected via frame-relay to R2 Method1: Frame-relay de-list command R1 Configuration R1(config)#access-list 1 permit !-- packets sourced from with size > 500 will have DE bit set R1(config)#frame-relay de-list 1 protocol ip list 1 R1(config)#frame-relay de-list 1 protocol ip gt 500 !-- assign the DE list to …

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Frame-relay traffic shaping using MQC

To apply frame-relay traffic shaping using a normal map-class, the command frame-relay traffic-shaping must be applied to the main interface. This method has a pitfall; the problem is that when you apply the frame-relay traffic-shaping command to the main interface any DLCI that has no explicit map-class will be shaped to 56K by default. This means that if you need to apply traffic shaping to only one PVC all other PVCs will be shaped to 56K by default. MQC shaping can be used to solve this problem by configuring shaping on specific PVC without the need to use the command …

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