Questions tagged [protocol-theory]

For questions about network protocols published in a Standard or RFC. Do not use this tag merely because the question mentions a networking protocol in it. Questions with this tag *could* be closed if they do not explain why the question is relevant and important to answer; this is necessary to avoid issues with tangential / trivial questions or help vampires.

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How does the encrypted Wi-Fi protocols relate to ethernet?

More exactly: Which protocol is embedded into which? The relevant Wiki page describes only the protocol, but not its relation to the ethernet. It isn't even made clear if it uses embedded ethernet ...
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2answers
3k views

What is the election process of Router ID in OSPF?

I am a little confused on the process OSPF uses to select the Router ID. Is following correct for the selection of the router ID in OSPF? Manual configuration Highest IP address on a loopback ...
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1answer
966 views

Difference between packet loss and ACK loss [duplicate]

I want to ask a question that seems to confuse me. I have a question in my self-study "Computer Networking" book which distinguishes a packet error from ACK error for a Selective Repeat protocol and ...
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1answer
756 views

why the two hosts with same “Subnet Address” in LAN can be pinged?

In Subnet Addressing of TCP/IP Illustrated, Vol. 1: The Protocols, there is description: This makes sense because class A and class B addresses have too many bits allocated for the host ID: 16384 - 2 ...
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Who assigns the Coordinator Node in Zigbee mesh network? [closed]

In the zigbee mesh network, who assigns the coordinator node and the FFD? Is there any algorithm by which this is done?
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1answer
83 views

Even after the spanning tree is determined why Root Bridge periodically send configuration message.

Even after the spanning tree is determined why Root Bridge periodically send configuration message.
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1answer
393 views

Estimating the round trip time

In "Computer Networks : A Top-Down Approach" by Kurose and Ross they say: Instead of measuring a SampleRTT for every transmitted segment, most TCP implementations take only one SampleRTT ...
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3answers
993 views

spanning tree at layer 3

we want to prevent loops in the network be it LAN or WAN. However for layer 2 LAN networks STP is used to prevent looping switches. However at layer 3 TTL field is used. why not use STP for layer 3 ...
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1answer
923 views

TCP error recovery

Consider two machines A and B, machine A sends 3 packets to B of sequence number 1, 2, 3 during transmission only packets 1 and 3 are received by B. Now B requests for packet 2, and machine A sends ...
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4answers
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The reason why TCP sends consecutive ACKs all together

While analyzing Wireshark capturing, I noticed that the sender or the receiver sometimes sends a bunch of consecutive ACKs together as oppose to what I have learned. I learned that for every packet ...
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1answer
339 views

Is a telegram different from a datagram?

I am reading about field buses and for instance the HART protocol and PROFIBUS call their level 2 frames telegrams. Is this on purpose to differentiate from datagrams (a term used for instance in the ...
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1answer
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What type of packet is 0x5577

I've been trying to find out what type of packet is 0x5577, based on this page. The following is a snapshot of the source code that indicates this values: f = myproto() f.timestamp = int(time....
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1answer
770 views

IPv6 Link-local addresses

RFC 4291 specifies that IPv6 link-local unicast addresses must have a high-order bit sequence of 1111111010, or fe80::/10. However, the same document specifies that the 54 bits following the first 10 ...
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1answer
831 views

Using the value of RTT to estimate the latency

Generally speaking, we can calculate the packet delivery time using this formula, Wikipedia: Latency = Transmission delay + Propagation delay + queuing delay + processing delay My question is: Is it ...
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1answer
501 views

What are currently used L2 and L3 protocols? (other than ethernet and ip4/6) [closed]

I heard about plenty of alternatives to ethernet like for example token ring, ARCNET, SONET, or to IP4/6 for example IPX but once I decided to look for software and hardware support I realized those ...
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1answer
6k views

Why is the minimum MTU of a IPv4 packet 68 bytes?

According to RFC791: Every internet module must be able to forward a datagram of 68 octets without further fragmentation. This is because an internet header may be up to 60 octets, and the minimum ...
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1answer
41 views

Already session between two computers before going through layers?

How can a computer have a session with another computer without going through the transport, network, data link and physical layers? I took this information from this video.
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1answer
325 views

Reverse Received Signal Strength Indicator (RSSI)

I am wondering what the Reverse Received Signal Strength Indicator (RSSI) is. I came across the term in the BEEKS Beacon's datasheet, under the heading "Bluvision BLE Stack Specification".
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1answer
2k views

Why is there reserved bit or byte in network protocols?

In different wire protocols there is often a set of reserved bits that must be set to 0 or else the connection is ended. What is the purpose of such reserved bits? When was the last time these were ...
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2answers
1k views

Can a subnet mask contain zeros between ones? [duplicate]

In theory, can a subnet mask have zeros between ones (e.g. 255.255.0.248) or it need to be strictly 1's followed by 0's? As stated in RFC 950, there is only an "example" to interpret an IP as <...
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2answers
371 views

Should all sent segments be requeued after a TCP retransmission timeout expires?

I am developing a TCP implementation and could not find a clarification to this in the relevant RFCs (793, 1122, 5681, 6298). When the retransmission timer expires, the first segment which has once ...
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2answers
407 views

What high level (above IP) protocol is used to return a response to an ICMP echo request?

I know ICMP uses IP datagrams to reply to echo requests but what is above that?
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2answers
241 views

The meaning of TCP port in the network context

When talking about ports, sometimes I read articles that state TCP port while others just say port. Are there some features that make TCP port different from other ports in the OS?
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3answers
3k views

Where does the code for the OSI layer protocols exist?

I know this might sound like a very amateur and stupid question but I don't understand the concepts of these protocols in the OSI model. Are they just code that gets invoked? Also where does this code ...
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2answers
2k views

Which part of IP header indicate net mask?

In IP header , Only the destination ip address and source ip address is indicated . How does a traveling packet know the network section of destination ip address in CIDR notation ? Thanks
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0answers
358 views

Why is an empty TCP segment at right edge of receive window not acceptable?

The TCPv4 specification (RFC 793) classifies a received segment as unacceptable if it has zero length, a sequence number equal to RCV.NXT+RCV.WND while the receive window is not zero (second row in ...
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2answers
684 views

OSPF Point-To-Point Question

I've consulted the spec https://www.ietf.org/rfc/rfc2328.txt and have googled to the end of the internet but I'm confused on OSPF Point-To-Point. If I have the following: Link State ID: 4.4.4.4 ...
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2answers
358 views

Do MSS/MTU violate the protocol stack layers independence?

We studied that the beauty of internet protocol suite layers is that each layer is responsible for a piece of the communication process. These layers provide services to adjacent layers and operate ...
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2answers
398 views

Two IPv6 global unicast addresses on the same interface (stateless and stateful)

Can I assign two global unicast address to the same interface, one obtained via stateful addressing (DHCPv6) and the other one via SLAAC (eui-64)? According to the RFC-4862: Both stateless address ...
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4answers
282 views

Why do we need a destination (server side) static TCP/IP Port?

This is probably an opinion based question which i know is frowned upon on here but here goes anyway. My question is as the title suggests. I can understand why we need an Ephemeral dynamic port on ...
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2answers
84 views

BGP RFC https://www.ietf.org/rfc/rfc4271.txt says from Idle a node can go to Active. Wikipedia says it can't

Which one do I trust ? :-) RFC: Idle state: Initially, the BGP peer FSM is in the Idle state. Hereafter, the BGP peer FSM will be shortened to BGP FSM. In this state, BGP ...
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2answers
60 views

Dr election in partial lan connectivity

Suppose we have three routers R1 R2 and R3 with full mesh connectivity in OSPF broadcast network (LAN). R1 becomes DR. R2 BDR and R3 is forming adjacency with both of them. Now let router r4 be ...
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1answer
760 views

For a TCP session, when is the first time an RTT measurement is sampled?

I am trying to understand the RTO mechanism. I have read RFC 6298, but it does not specify when the first RTT measurement is made. Consider the following packet exchange Client -----Syn-----> Server ...
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1answer
261 views

IPv6 - RA prefixes and flags

I'm trying to understand how SLAAC works, but having troubles understanding how the information inside the Router Advertisement is used by a client. Let's say neither the Manager nor the Other ...
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1answer
4k views

changing routing protocols administrative distance

Hello i have one doubt 1.if there are four protocols connections for instance rip,OSPF,static,and direct which routing protocol would be used , although it will take one with lowest administrative ...
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2answers
282 views

IS-IS multi-area

It is well known that an IS-IS L1 router chooses the nearest L1/L2 router to route inter-area traffic, if there is no route leaking as defined in RFC 2966. However, providing that there is no route ...
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1answer
16k views

Why only after 3-duplicate ACK retransmission takes place in TCP?

Is there any reason of choosing "3" only for retransmission. why not 2 or 4 or any other number?
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5answers
917 views

How we can assume which network protocol is working in which OSI Layer?

For a long time, I have this kind of silly question: How we can say some network protocols are working in X layer of the OSI model? For example, HTTP working in L7 of OSI, OSPF is L3, ICMP is L4, TCP ...
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1answer
200 views

IP packet reading

Just got an simple question.Its abt reading a plane IP packet. In a standard IP packet RFC 791, there are multiple fields, the IP packet header size is 20 bytes. Now when i look at following packet ...
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1answer
173 views

Purpose of the Transport Layer from a Conceptual Perspective

I have just started learning about the different layers of the Internet. As I understand it, the Transport layer is responsible for extending the Network layer's host-to-host delivery service to ...
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1answer
248 views

Is there ever an occasion where a host will respond to a RST or RST/ACK packet with an ACK?

The question is fairly simple, and maybe a bit remedial to most reading this, but I've been searching the web for something definitive about this point. I understand that the RST flag is intended ...
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2answers
2k views

How can a DHCP OFFER message be unicast?

Why is a DHCP OFFER message is destined to IP: 10.0.0.21 (which was assigned to my PC by DHCP server later) before even the system configured it? When the host is still asking for an IP address, how ...
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1answer
749 views

Stop-and-Wait ARQ algorithm

In the Stop-and-Wait algorithm, the sender needs to re-transmit the frame if the acknowledgement received is corrupted during transmission. But just the fact that the sender received an ...
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1answer
2k views

Why is the NDP Neighbor Solicitation message sent to the solicited-node address?

As I understand it, when Host Alice knows Host Bob's IPv6 address but not its MAC, Alice sends an NDP Neighbor Solicitation (NS) message to the solicited-node multicast address for Bob. Alice knows ...
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3answers
8k views

Can two different applications bind the same port on a host if they use different protocols?

So my question is quite clear I think. If two applications use different transport layer protocols (e.g. TCP and UDP or something else) can they open the same port number? How does the OS do the ...
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1answer
84 views

Five consequtive SYN-messages from client to server

the 5 packages 333 -> 337. What are those and why does the client do this? More generally, why does the client send five SYN-messages to the server?
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3answers
5k views

Usage of Flow label in IPv6 header?

I have been reading the IPv6 Flow Label Specification (RFC 6437) and I would like to ask about the purpose of setting this label. In case of just using the 2-tuple (source address, destination ...
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4answers
2k views

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page?

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page (same layer as IP) when the ICMP protocol data is a payload of the IP packet? This is the article on Wikipedia that states ...
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1answer
70 views

IP Protocol left for development

I'm designing a custom application, which needs a custom IP packet. In order to identify the traffic, I need an open protocol number, left for development. In layer 2, I used the 0x88b5 : "available ...
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1answer
781 views

How is inter-area routing carried out in OSPF?

If all the areas learn routes to the other areas through Area 0, does it mean that two non-backbone areas cannot communicate with each other? What does ABR do then?

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