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8 votes
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The Reasoning Behind TCP and UDP Multiplexing Tuple

From a host stack's perspective, different local IP addresses mean different logical interfaces on the network layer. Whether they are bound to a single or multiple physical interfaces is of little ...
Zac67's user avatar
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6 votes
Accepted

In IPv4 Fragmentation, should the first block be necessarily the closest smaller multiple to 8

The Fragment Offset field is three bits smaller than the Total Length field. 2^3 = 8 That means that you must use a multiple of eight. Typically you will use the largest multiple of eight that fits ...
Ron Maupin's user avatar
  • 99.8k
6 votes

The Reasoning Behind TCP and UDP Multiplexing Tuple

You assume a host has one, and only one, IP address. This is rarely true. If you count loopback, which every machine has, there will always be at least two. In the modern world, it's very likely you'...
Ricky's user avatar
  • 32.3k
5 votes
Accepted

Advertising IP prefixes to the internet using BGP

You're only looking at IPv4 I guess, all RIRs have more than enough IPv6 ranges available. Most RIRs (maybe all by now) don't have any unused IPv4 ranges available anymore. But some do have a waiting ...
Teun Vink's user avatar
  • 17.4k
3 votes

The Reasoning Behind TCP and UDP Multiplexing Tuple

A server can have multiple IP addresses, even if it only has 1 NIC. In fact, every host has at least 2 IP addresses: The host's Layer 3 identifier, and the host's loopback address. A service can ...
pepoluan's user avatar
  • 131
3 votes
Accepted

No access to internet via DHCP, but works with manual IPs

Ok, maybe this was a silly mistake, but in the DHCP server settings there was a field called "router" that I didn't know what it was, so I left it blank and forgot about it. This was the &...
Mike's user avatar
  • 133
2 votes

Advertising IP prefixes to the internet using BGP

RIRs have long since run out of IPv4 addresses (between 2011 and 2019). You'd need to obtain a (pricey) IPv4 block on the open market. IPv6 addresses are readily available from the RIRs, of course.
Zac67's user avatar
  • 85k
2 votes
Accepted

Understanding IPv4 model of operation

An IP packet (OSI layer 3) isn't encapsulated by another IP packet but by a data link layer frame (OSI layer 2). It is that frame that is addressed to the next-hop destination - either the gateway ...
Zac67's user avatar
  • 85k
2 votes

What TTL value should i use to make sure the packet never leaves the broadcast domain

Packets with TTL 0 will be dropped at the interface. Link-local protocols, like multicast (by default), use a TTL of 1 to be confined to the broadcast domain.
Ron Maupin's user avatar
  • 99.8k
2 votes

Can two separate computers connect over 127.X.X.X IP range?

No, that's generally not possible. 127.0.0.0/8 is local to a host only, see RFC 1122. None of those addresses can be used over a physical link. If you're looking for a link-local address, that's 169....
Zac67's user avatar
  • 85k
2 votes
Accepted

Layer 3 Switch IP Problem on Packet Tracer

You have the same IP addresses on both switches. This is an invalid configuration. Each interface needs a unique IP address. If you need one gateway address for your devices, consider using a First ...
Ron Trunk's user avatar
  • 67.7k
2 votes

In IPv4 Fragmentation, should the first block be necessarily the closest smaller multiple to 8

For IPv4, see RFC 791: To fragment a long internet datagram, an internet protocol module (for example, in a gateway), creates two new internet datagrams and copies the contents of the internet header ...
Zac67's user avatar
  • 85k
1 vote

What exactly does the term "main network" mean in subnetting?

Based on your description, you probably mean the network address. That is the address where all the host bits are set to 0. It is used to refer to all the possible addresses as a whole. You may find ...
Ron Trunk's user avatar
  • 67.7k
1 vote

The Reasoning Behind TCP and UDP Multiplexing Tuple

Because the receiver address is required to uniquely identify a given flow. Consider the case where two different clients connect to the same web server, and they happen to pick the same ephemeral ...
Austin Hemmelgarn's user avatar
1 vote

Do destination hosts decrement the TTL?

A proper IPv4 implementation should also look at the intention of RFC 791: The intention [of the TTL mechanism] is to cause undeliverable datagrams to be discarded, and to bound the maximum datagram ...
Angelos Vassiliou's user avatar
1 vote

Do destination hosts decrement the TTL?

As of RFC 791 (emphasis mine): The Time to Live is an indication of an upper bound on the lifetime of an internet datagram. It is set by the sender of the datagram and reduced at the points along ...
Zac67's user avatar
  • 85k
1 vote

What TTL value should i use to make sure the packet never leaves the broadcast domain

See RFC 791: If the time to live reaches zero before the internet datagram reaches its destination, the internet datagram is destroyed. Accordingly, a packet with TTL=0 can only be processed locally ...
Zac67's user avatar
  • 85k
1 vote
Accepted

Too many mac addresses in a switch - Cisco Packet Tracer

That sounds normal. When a host first comes up, it may try some broadcast communication, e.g. DHCP. After, it will not need to do that, so clearing the MAC address tables will remove it until there is ...
Ron Maupin's user avatar
  • 99.8k
1 vote
Accepted

Why can't we use large-scale NAT system with thousands of private IP addresses assigned to a single public IP

We can and we do. For lookup efficiency, you'd want to use each public-facing transport-layer port (TCP, UDP) per IP address only a single time. That limits you to roughly 64,000 connections per ...
Zac67's user avatar
  • 85k
1 vote

Is a private network the same concept as a network which uses private IP addresses inside it?

Depending on the context and your own preference, a private network is usually one that uses private network addresses. The term may also be any network that is not open to the public to route into or ...
Zac67's user avatar
  • 85k
1 vote

How can I have multiple servers and IPs if I only have 1 ip with gigabit connection?

How can I have multiple servers and IPs if I only have 1 ip with gigabit connection? Up to the network layer (L3), you can't. You can employ transport layer (L4) ports, ie. use a destination NAT ...
Zac67's user avatar
  • 85k
1 vote

IP fragmentation and PMTUD

The ICMP header is at the beginning of an IP packet. Since fragmentation doesn't change the IP packet itself, the header needs to be present in the first fragment. Whatever you think you've seen must'...
Zac67's user avatar
  • 85k
1 vote
Accepted

Would a /24 public ip range typically be from the same country?

/24 is the longest prefix you can advertise over BGP, so it's generally atomic within an AS. However, there's nothing stopping the AS from routing each single address to different parts of the globe. ...
Zac67's user avatar
  • 85k
1 vote

What is hiearchy of IP addresses?

IP addresses are hierarchical for delegation only. You can add bits to a delegated prefix, breaking it into smaller subnets which can then be used or re-delegated. You cannot use that information for ...
Zac67's user avatar
  • 85k
1 vote
Accepted

The TTL and packet drop

When a router receives a packet with a TTL of 1, the router can still process and accept it if its destined for itself, correct? Yes. Because for example, eBGP messages use a TTL of 1 by default and ...
Zac67's user avatar
  • 85k
1 vote

ISP ARP tables and routing

ARP is used to resolve a MAC address from an IPv4 address for network that use MAC addressing, and it is local to that network. MAC addresses are only seen or relevant on the specific network they are ...
Ron Maupin's user avatar
  • 99.8k
1 vote

How does a router know the destination mac?

Sender doesnt know MAC address of the destination and it doesnt need to. It only needs to know MAC address of the router which will route packet to the next subnet. So packet hops from router to ...
Dražen Grašovec's user avatar
1 vote

OSI layer of Neighbor Discovery Protocol

NDP belongs to the OSI layer 3 (Network layer) and TCP/IP layer 2 (Internet layer), why? NDP is routable Since NDP runs on ICMPv6, and ICMPv6 is routable since it runs on IPv6, NDP can be routed ...
Anim Mouse's user avatar
1 vote

RIP v2 Network Command

Unless you include the no auto-summary command in the RIPv2 router process, RIPv2 will assume classful networks the way RIPv1 does. I have not seen either of those labs, but it seems that the Neil ...
Ron Maupin's user avatar
  • 99.8k
1 vote

What does "Configure kernels to not follow the RFC 5681 SHOULD" mean?

See RFC 5681, and RFC 2119 for the IETF usage of MAY, SHOULD, MUST.
Zac67's user avatar
  • 85k

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