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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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2 answers
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What is the point of Wi-Fi association?

In the 802.11-2020 standard, you can read, regarding 802.11 Association To deliver an MSDU within an ESS via the DS, the DS needs to know which AP within the ESS to deliver the MSDU, so that the MSDU ...
3 votes
3 answers
422 views

Why is delayed segment prevention (TIME_WAIT) in TCP only done for one side?

One of the reasons for TIME_WAIT is to prevent old packets/duplicates, coming in late, to screw up subsequent connections on the same (src ip, src port, dst ip, dst port) quadruplet. That makes sense, ...
8 votes
2 answers
2k views

Why is the IPv6 link-local address range fe80::/10 rather than fe80::/64?

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 ...
1 vote
2 answers
60 views

Missing ICMP identifier equivalent in ARP protocol and desired arping behavior

Running simultaneously more arping on the same interface and the destination IP address all clients get the responses due missing ICMP identifier equivalent. First, am I correct that there is no ICMP ...
10 votes
5 answers
12k views

Why is the protocol field part of an IP header?

Note this is not a duplicate of Why is the IP layer aware of higher layers in the network stack? The need for a protocol identifier (eg. the IP header's Protocol field) in packet-based communication ...
0 votes
1 answer
346 views

In HDLC, how to recognize bit stuffing?

In framing for the HDLC protocol, assume the receiver receives the following string of bits: […] 011111010 […] How can it realize whether the sequence “011111010” is real data, or the result of a bit ...
1 vote
1 answer
80 views

Recognizing the next protocol in MPLS header

How can I know what is the next protocol in MPLS header? I do know that MPLS header does not provide any information about the next protocol, But I somehow need to know how to recognize it, as I am ...
1 vote
2 answers
258 views

what is the purpose of GRE in UDP encapsulation if its unidirectional

I was going through this feature of GRE called GRE-in-UDP encapsulation. The RFC says it is unidirectional and the tunnel traffic is not expected to be returned back to the UDP source port values used ...
1 vote
1 answer
51 views

Does PPP do broadcasting? [duplicate]

Let's consider the scenario below: Router 1 <---> Router 2 <---> Router 3 Routers 1 and 3 establish a link with router 2, then will Router 2 broadcast to the interface connected to routers ...
3 votes
1 answer
112 views

Address Field In PPP Protocol

What is the actual use of the Address Field on PPP As I know, it is always set to 11111111 and this doesn't seem to have any purpose because we use ppp we dealing with the direct link communication
0 votes
1 answer
67 views

On what basis does a router actually install GRE headers and remove them?

I am learning about networks and I have reached the topic of tunnels. At the same time, I have a need to set up a GRE (Generic Routing Encapsulation) tunnel between a remote server (to route addresses ...
1 vote
3 answers
2k views

Sequence numbers of segments in three way handshakes of TCP connection establishment or termination

I was trying to understand TCP connection establishment and termination steps from Forouzan's book. In third step of three way handshake of connection establishment, it says following The client ...
2 votes
3 answers
2k views

What's the use of an acknowledgement number without the ACK flag set?

Isn't it redundant if the ACK flag in the header isn't also on? Do you ever mix an acknowledgement with a normal message - send data and acknowledge a message in the same TCP segment? I feel like ...
1 vote
2 answers
104 views

rules regarding IPV4 fragments and piecing them together

I'm rolling off my own TCP/IP stack for DOS and I have a question on IPV4 packets. Assuming that a client sends multiple IPV4 fragments, I would predict the MF flag would be set for every fragment ...
15 votes
7 answers
56k views

Is a DHCP offer packet a broadcast or unicast?

DHCP OFFER is a layer3 broadcast because the server doesn't know the client's IP, but the server knows the client's MAC address. So why does it send the OFFER as L2 broadcast? If anyone ask me about ...
4 votes
2 answers
1k views

Why two routers connected via PPP don't use ARP but Ethernet requires ARP?

I have read from @Ron Maupin's answer of this question that your two routers are connected via PPP (this is not uncommon), ARP will not be used , but if the two routers are connected via ethernet, ...
0 votes
0 answers
31 views

Conflicting opinions for route aggregation [duplicate]

I am a student and I came accross this question: An ABR in OSPF has in its range networks 10.0.8.9/24 to 10.0.21.0/24. how can it summarise the networks? not necessarily in one prefix. What we ve ...
3 votes
1 answer
921 views

How PoE interacts LLDP and LLDP-MED?

I need to research 802.3at PoE PSE capable equipment for a project in my company's network, but I have some knowledge gaps regarding PoE operation and its reliance on LLDP. I took a look over 802.3-...
13 votes
2 answers
4k views

Why does Ethernet use EtherType field to determine what type of packet is in a frame instead of just looking at the packet header?

I'm studying for some networking concepts and have learned that a receiving host looks at an Ethernet frame's header to determine what protocol being used by the packet. It makes me wonder though, ...
0 votes
1 answer
18 views

How can GMPLS unify signalization plain of all telecommunications network technologies?

In what way can GMPLS do that unification of signalization of network technologies, by hardware, like MPLS switches, or by network protocols? And what is the role of optical networks in GMPLS? Are ...
5 votes
2 answers
6k views

Understanding the difference between EUI-64 and IPv6

I understand that Extended Unique Identifier (EUI-64) allows a host to automatically assign itself a 64-bit interface identifier IID for an IPv6 address. My question is: What is the purpose of using ...
3 votes
2 answers
2k views

Rationale for EXCLUDE mode in mutlicast IGMPv3 / MLDv2

Both IGMPv3 and MLDv2 have an include and an exclude mode, where a multicast listener can specify to either listen only for packets from some list of source addresses (include) or only for packets ...
1 vote
1 answer
809 views

The use of a link local IPv6 address

In a networking course that I'm following, there was a mention of several ways of how IPv6 link local addresses can be used, such as Assigning the link local address of a router/L3 switch as the ...
38 votes
3 answers
21k views

Why does the IPv6 header not include a checksum?

It is stated in Wikipedia that an IPv6 header does not include a checksum. What are the reasons that were behind this decision?
-2 votes
4 answers
15k views

How Layer-2 data will be fragmented?

Got a doubt while studying about LLC layer. From Network layer I came to know that IP fragmentation will be done, For L4 TCP will segment the data. Here, the question is Protocols starting from Layer-...
7 votes
2 answers
6k views

Ethernet's frame format, length or EtherType?

Ethernet defines a 2 byte header for the payload's length in its frame format. This header has an ambiguous meaning: if smaller than or equal to 1500 it represents the payload length. if ...
1 vote
1 answer
78 views

Is there a term for application layer protocols that are responsibilities of network engineers?

In studying network engineering, it is usually taught that network engineers are responsible from physical layer up to transport layer, that is, layer 1-4 only. Obviously, HTTP or HTTPS are off-topic ...
3 votes
1 answer
164 views

Valid uses for IPv4 Options [Community-Wiki]

Engineers building firewall rules often block all IPv4 packets with IPv4 Options set in the header. However, there are a few common and valid use-cases for IPv4 Options. This Q&A is intended to ...
17 votes
2 answers
29k views

What is the difference between Ethernet II and 802.3 Ethernet?

Can anyone explain to me what is the difference between Ethernet, Ethernet-II and 802.3 Ethernet. I referred to a lot of books, they are in high level language. Can anyone explain to me in a simple ...
10 votes
3 answers
12k views

Is Ethernet a protocol?

When I googled I found a lot statements about this. Like.. Ethernet is not an application protocol. But I'd still give it the description "protocol". A network protocol defines rules and ...
41 votes
5 answers
39k views

Why was the MTU size for ethernet frames calculated as 1500 bytes?

Why was ethernet MTU calculated as 1500 bytes? What specific calculation was done to arrive at 1500 byte ethernet MTUs, and what factors were considered for that calculation?
19 votes
4 answers
26k views

Why does WLAN use Collision Avoidance and not Collison detection?

I am searching for this answer for quite some time now. Why there is CSMA/CD in LAN but CSMA/CA in WLAN? The best explanation I could find is "due to extreme ratio in transmitting and receiving power,...
2 votes
1 answer
59 views

Can a BGP speaker records alternative paths to the same destination?

The BGP RFC 4271 reads : In the context of this document, we assume that a BGP speaker advertises to its peers only those routes that it uses itself (in this context, a BGP speaker is said to "...
0 votes
0 answers
135 views

How does QUIC encrypt packets containing multiple CRYPTO frames?

TCP is slowly being replaced by QUIC and I'm implementing a component that looks at QUIC packets to extract the server name indication from initial packets. The code is working fine, assuming that: (1)...
1 vote
1 answer
374 views

How does QUIC provide delivery guarantee?

I'm struggling to grasp how QUIC implements handshakes in contrast with 3 handshakes in TCP. I came across with this picture on Wikipedia. As QUIC uses UDP, I don't understand how the protocol ensures ...
10 votes
4 answers
11k 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 address)...
5 votes
2 answers
22k 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?
3 votes
1 answer
263 views

Does Network Discovery (rfc2461) preclude ARP sniffing?

I'm debugging a system demonstrating intermittent loss of connection. It's loosing entries from the neighborhood cache while there are active connections. Does Neighbor Discovery (rfc2461) require ...
0 votes
1 answer
120 views

How router will send ARP resolve packet when it receive ARP request?

How router will send ARP resolve packet when it receive ARP request ?? Router by default enabled with proxy arp configuration?? If then proxy arp is not configured then what will happen if it receives ...
3 votes
3 answers
671 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 ...
0 votes
2 answers
624 views

Does window size in tcp header include tcp header size?

Let's say a TCP segments has in the field of "window size" = 1400 bytes. Does that mean that we can send 1400 bytes counted in tcp segments = TCP headers + data or it does specify only ...
1 vote
2 answers
1k views

TCP Three Way Handshake?

I have the following query about the tcp handshake. To establish a connection the server must send a packet with SYN flag to 1 Then the server replies with a SYN,ACK flag to 1 , and afterwards the ...
1 vote
2 answers
207 views

Pros and cons of the idea of parallell data transmission

I am learning the basics of internet protocols and related principles. I recently performed experiments comparing UDP and TCP. But when I did that (using the ttcp program) it was only one process and ...
2 votes
1 answer
559 views

Why SYN-RECEIVED sends reset on not acceptable ACK?

The tcp protocol actions on arriving segment vary. The set of choices includes: silently drop segment kill connection (i.e. enter CLOSED) send reset (and maybe kill connection) send dup/null ack (etc)...
1 vote
2 answers
1k views

How is P actually chosen in P-persistent CSMA?

I am struggling to understand how the probability value P is chosen for P-persistent CSMA for any particular station, what's the logic behind this.I have read from Wikipedia . P-persistent This ...
1 vote
1 answer
139 views

Is the EAP-Request/Identity and EAP-Response/Identity transmitted in the clear in a WPA2 entreprise Wi-Fi setup?

Looking at the WPA2 (Entreprise, let's say PEAP-MSCHAPv2) Wi-Fi protocol, I understand that since WPA2 uses Open System Authentication, and that 802.1X authentication takes place before the 4-way ...
0 votes
1 answer
2k views

Size of an ethernet frame carrying an arp request using ip (no options) & ethernet?

OKay so I found that this frame has size 72 bytes with no explanation and I can't seem to be able to figure out why . Ethernet payload will be : ip header + arp packet Arp packet with ip & ethrnet ...
-1 votes
1 answer
40 views

802.11 Protocol on Different Frequency [closed]

Wifi (and the 802.11 protocol) takes place on 2.4Ghz and 5Ghz frequencies. Is it possible to recreate this protocol on a different frequency (say 500Mhz) and create a functional network using a modded ...
1 vote
0 answers
240 views

Diffie-Hellman with PSK/PKI in the context of IKEv1

It seems I fail to understand few things about DH's functionality in the context of IKEv1. A little bit of context first: During IKE Main Phase, with the 3rd and 4th messages, the peers each exchange ...
5 votes
2 answers
4k views

What is the difference between connect and active states of BGP?

What is the significance of having two different states in FSM when both try to establish TCP Connection?

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