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20 votes

Worst-case efficiency of PPP escaping mechanism

You might care to read RFC 1547 "Requirements for an Internet Standard Point-to-Point Protocol" which explains how the PPP was chosen. The thing I'd suggest you are missing is that ...
jonathanjo's user avatar
  • 16.3k
18 votes

Why does PPP need an underlying protocol?

Why does PPP need a wrapping protocol? PPP is not a layer-1 protocol, so it needs a layer-1 protocol to carry it. Protocols like ethernet are both layer-1 and layer-2 protocols, so PPP can use ...
Ron Maupin's user avatar
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12 votes

Why does PPP need an underlying protocol?

PPP is designed to ride on top of a byte-oriented, point-to-point physical-layer protocol like a simple modem-style serial link. Ethernet is no simple serial protocol but it requires frame-level ...
Zac67's user avatar
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10 votes

Why PPTP, L2TP, PPPOE are in OSI Layer2?

PPTP, PPPoE, and L2TP all provide OSI Layer 2 services. That is, the user of these protocols (usually, a network layer protocol suite) thinks it's running over a "normal" link layer. ...
Jeff Learman's user avatar
6 votes
Accepted

Why does PPP need an underlying protocol?

( As others have already said, PPPoE is literally PPP over Ethernet. And similarly PPPoA is PPP over ATM. ) Ethernet and ATM are oddities in the networking world as they define both a layer-1 and ...
Ricky's user avatar
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5 votes

What is a "rotary dialer" in the context of dialup connections?

In the 1990s in a British regional ISP, we had a choice from the telephone company of getting two settings for multiple lines: In the ordinary hunt group, the next incoming call would arrive on the ...
jonathanjo's user avatar
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5 votes

What is a "rotary dialer" in the context of dialup connections?

From the HOWTO you linked: rotary dial in set of telephone lines When I wore a younger man's clothes, back in the late 1990ies, I ran a bunch of Shiva LAN Rovers (in their IBM guise labelled as ...
Marc 'netztier' Luethi's user avatar
5 votes
Accepted

What is PPP and why does it not have a MAC address?

PPP is a data link layer protocol that's designed to run on top of a simple serial link as physical layer. Since there are exactly two nodes on that point-to-point link, no addressing is required. The ...
Zac67's user avatar
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4 votes

How is the length of a PPP frame known?

Sure, there is a 2-byte checksum followed by a magic byte, but that is hardly collision-proof. Occurrences of the magic byte are escaped. There are two types of escaping used, called "character ...
sourcejedi's user avatar
4 votes
Accepted

How do protocols like PPTP, L2TP work below IP level

In real life, you can't stick to the OSI model entirely. It's helpful and necessary as a guide on how to structure the components in a complex network but you can't always say that's layer x. ...
Zac67's user avatar
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4 votes
Accepted

Why are the Address and Control fields constant in PPP protocol?

The address and control fields were designed with future changes in mind, and other values "may be defined at a later time, or by prior agreement." (RFC 1662 "PPP in HDLC-like Framing&...
jonathanjo's user avatar
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4 votes
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How exactly does CHAP authentication work?

CHAP is defined in RFC 1994. You concatenate the identifier, the password (secret), and the challenge, in ASCII, in that order. The response is hashMD5(identifier.secret.challenge), sent in binary (16 ...
Zac67's user avatar
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3 votes
Accepted

Is PPP a useful choice for fiber connections?

PPP is a protocol for transporting higher-layer protocols (like IP) over a simple serial interface. Since you'd already be running Ethernet, PPP doesn't work and is of no use anyway. You could use ...
Zac67's user avatar
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3 votes

Assigning static IP addresses to dialin PPP users on Cisco IOS

Actually this is relatively easy. Yes, you need AAA, but you don't need an external server. aaa authentication ppp default local aaa authorization network default local aaa attribute list Static-1.2....
Salrissa Jenkins's user avatar
3 votes

PPP, Ethernet and PPPoE differences

The main point of using PPPoE is to have an authenticated session, a concept Ethernet by itself doesn't have. That allows an ISP to concentrate packets from many users in their backhaul network and ...
Zac67's user avatar
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3 votes
Accepted

IPv6 in PPP - should be an Interface Identifier negotiated FOR both ends of a link? Clarification of RFC 5072 needed

...upon completion of the negotiation, different interface-identifier values are to be selected for the ends of the PPP link. In other words, by the time the negotiation is done, the two ends of ...
mere3ortal's user avatar
  • 2,416
3 votes
Accepted

Why is L2TP based on PPP and not PPPoE?

PPP is independent of the underlying transport, PPPoE requires to be run on Ethernet (or a like tunnel). But of course, you can also run L2TP with PPPoE (RFC 3817).
Zac67's user avatar
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3 votes
Accepted

How is the length of a PPP frame known?

The PPP header starts with a 16-bit protocol id. You need to look at that first in order to know how to interpret the rest. If the protocol id is LCP/IPCP/IPv6CP then the header structure typically ...
StackedCrooked's user avatar
3 votes
Accepted

PPP, VPN, Tunneling and OSI model

Your question is really too broad, and home networking and consumer-grade devices are explicitly off-topic here, but I will try to give you some general answers. PPP is a layer-2 protocol, the same ...
Ron Maupin's user avatar
  • 99.9k
3 votes
Accepted

What is SLIP good for?

SLIP was an early protocol (mid-1980s) for running IPv4 over a serial line. It was very cumbersome due to both sides requiring identical configuration and compatible SLIP versions. It was succeeded by ...
Zac67's user avatar
  • 85.4k
3 votes
Accepted

How PPPoE uses addressing to know destination Mac address?

You're getting too hung up on the ethernet side of the equation. Yes, ethernet is a multi-point medium. PPPoE does not use it that way. The PPPoE discovery/setup process creates a single, one-to-one ...
Ricky's user avatar
  • 32.3k
3 votes
Accepted

Address Field In PPP Protocol

As you have guessed the PPP address field was defined by RFC 1662 and has no function. It must be all ones according to the RFC or it should be silently discarded. Address Field The ...
Mike Pennington's user avatar
2 votes
Accepted

PPP sessions on packet return?

Yes - the BRAS is both stripping the PPP[oE] frame (...and some L2/L3 underlay information, depending on the design in use) off of frames coming from the subscriber device and is adding both the PPP[...
rnxrx's user avatar
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2 votes
Accepted

Configuring PPPoE client through OMCI on Huawei ma5608T

I work for Huawei and I have configured PPPoE, both client and server, recently for an AR200 router, to be honest with you, I don't know how much of a difference exist between my equipment and yours. ...
Antonio Perez Oseguera's user avatar
2 votes
Accepted

Why are /30 subnet used for PPP connections?

A /30 subnet is used for the two public IP addresses. Couldn't they just route our two IP addresses over our PPP link as isolated addresses that don't belong to any subnet? If my understanding is ...
hertitu's user avatar
  • 2,658
2 votes
Accepted

PPP, Ethernet and PPPoE differences

1) Can I use PPP to connect to my router from PC? If no, then why? That depends. If you have network interfaces in your PC and router that support PPP, then yes. 2) Why I need PPPoE? Where it is ...
Ron Maupin's user avatar
  • 99.9k
2 votes

Assigning static IP addresses to dialin PPP users on Cisco IOS

No. The only way to set the address per user is with AAA (radius/tacacs) There used to be ways to pin an address per line, but it's never been possible by user. – Ricky Beam I believe Ricky Beam's ...
Juffo-Wup's user avatar
  • 181
2 votes
Accepted

can two devices communicate without physical layer?

can 2 device communicate with each other without data going to physical layer? No. The physical layer is the one actually doing the bit lifting. Without physically transporting the data to another ...
Zac67's user avatar
  • 85.4k

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