74

DHCP cannot use TCP as the transport protocol because TCP requires both end-points to have unique IP addresses. At the time a host is required to use DHCP, it does not have an IP address it can source the packets from, nor does it have the IP address of the DHCP server. So it uses 0.0.0.0 as the source IP address and 255.255.255.255 (broadcast) as the ...


42

On a similar question here Luke Savage explained it perfectly: Traceroute is not a protocol itself, it is an application and the protocols used depends on the implementation your are using. Primarily this is ICMP. There are two main implementations: tracert - tracert is a Windows application that utilises ICMP packets with as incrementing TTL field to map ...


24

Since the source has no IP address (0.0.0.0) and the destination is everyone (255.255.255.255), it's hard to see how you would identify a particular session. But even if you could, what would be the benefit? The data in a DHCP message is quite small (~300 bytes), so it can easily fit into a single segment. It's not worth the overhead to establish a TCP ...


22

Suppose you have two NICs with the same MAC address, but not necessarily the same IP address. You can't have that within the same link-layer segment. Identical MAC addresses will disable reliable switching/bridging. What is the least possible separation (in terms of number of switches, routers, different IP subnets etc.) needed that would still allow ...


19

There are multiple reasons why TCP wouldn't work for DHCP(v4.) First of all, TCP is connection-oriented. A TCP connection is defined between two particular hosts. However, when a DHCP client first starts up, it doesn't know which host(s) it wants to talk to. Its only option is to broadcast a DHCP DISCOVER message to all hosts on the local network. ...


18

To add to @naïveRSA's answer, if there's filtering/firewalling in the path one could also have the situation where an ICMP "echo reply" (ping) packet is blocked, but an ICMP "time exceeded" (tracert) packet is allowed. This would give the same results even when only ICMP (Windows) is used. In both cases (sender using either UDP or ICMP) the error ...


14

It depends. While many Ethernet PHYs transmit data in a purely serial fashion (e.g. 100BASE-TX, 1000BASE-SX, 10GBASE-SR), some split the data stream into multiple lanes that are transmitted in parallel. Most commonly, 1000BASE-T - the common gigabit-over-copper variant - splits the encoded data stream into four lanes and transmits each separately on one of ...


13

Let's ignore the Gigabit part for now, and focus on your "2 devices are sending at the same time" part for a bit. On shared media, this can actually happen and be a problem. Most wireless transmissions are shared media, and Ethernet, back in the day, used to be: 10base2 (coax) used what was more or less a single cable with every one on it. Obviously, two (...


12

This particular case is a complex one. Regarding 1000baseT. First: when we say in general that two devices are transmitting at the same time, they are not normally actually sending bits at the same instant on the same medium. If they do so, there is a collision and all the listening devices work this out (eventually, through various collision detection ...


12

The requirement exists to prevent collisions. This is a bit more important than most people recognize. Even if you have systems which currently don't communicate with other systems over the internet you still need your addresses to be globally unique. You may now or in the future need to add a host which can communicate both with your internal network and ...


12

Yes, encapsulation hide the details of what is encapsulated and doesn't really care about the payload nature. VxLAN is a sensible example of this, with layer2 (VLAN) being encapsulated in layer 4 (UDP).


10

You can have high speed, but if you have to go through a long distance then you have also high latency. Let's use Los Angeles and London to understand this: The distance from Los Angeles to London is around 9,000 kilometers.(The shortest path). A geostationary satellite is 35,800 kilometers above the earth. The satellite is roughly 4 times farther than ...


10

When companies merge or set up an extranet to communicate, it has proven difficult with IPv4 Private addressing because the companies often use the same or overlapping address space, and that requires the ugly hack of NAT to get around, and that can cause problems and break many protocols. This was identified as a problem when IPv6 ULA was being developed, ...


10

Are uplink ports simplex ? Hub interfaces are simply hub interfaces, there really are no uplink interfaces. Why is it not possible for the hubs to read from the uplink port and broadcast the frame to the remaining ports ? Hubs are stupid. They simply copy the signals received on any interface to all other interfaces. They do not read anything, and they ...


10

To add to Ron's point - a hub (...or a number of hubs) basically models the behavior of the original Ethernet, which is to say basically a big piece of coaxial cable. If one station transmits, all the others receive. When a station wants to transmit, it waits for an opening. If multiple stations try to transmit at the same time then a collision occurs and ...


9

Welcome to Network Engineering! If I understand your question, it's "can my network devices communicate on a single LAN using APIPA addresses? The answer is YES. APIPA addresses are in the 169.254.0.0/16 range, so every device is in the same subnet, and therefore same broadcast domain. If fact, this is exactly what APIPA was created for: to allow hosts ...


9

The Maximum Segment Size is the largest TCP segment that can be transported in a single IP packet. It is derived from the Maximum Transfer Unit (MTU) minus IP header overhead minus TCP header overhead. For TCP over IPv4 over Ethernet without options, that's 1460 bytes. The TCP window size is the amount of data "in flight", ie. being transmitted before an ...


9

Consider a package delivery service, like UPS or DHL. They don't care what's inside the box - they just make sure it gets to its destination. Similarly, the protocol doesn't care what the payload is. It doesn't have to be a higher layer. The idea of a layered protocol model is that the "payload" of a layer can be anything. @JFL gave one example. ...


8

There is no single precise definition for a "link". A link can be a physical layer connection, two ports connected by a cable. A link can also be understood as general connectivity by data link layer, ie. point-to-multipoint (as in "does the VLAN link over that trunk?" or with an aggregated link). The TCP/IP model defines the link layer as the one below ...


7

Latency is really just distance: the time it takes for the beginning of a bit to leave here and arrive there. (As perfectly explained in the other answer) this is entirely unrelated to speed: it takes approx 240 ms for the signal to start arriving on a satellite link, whether it's going at 1 bit/second or 1 Mbit/second. The beginning of the message takes 1 ...


7

A wireless network is only a single, shared medium with a limited total bandwidth. The more clients compete for bandwidth the smaller each slice gets. Additionally, the simple presence of clients consumes bandwidth = air time. It's not much per client but it sums up. Also, more clients also mean more potential senders, so that collisions become more likely....


7

Assuming all wired ethernet links here. When two devices on the same network segment send at the same time, no matter who they send to, that's called a collision. Neither message gets through when a collision happens. Fortunately, senders have the ability to detect collisions. When it happens, each sender will each pick a random amount of time (small ...


7

The situation you describe is very similar to what cost Target* many millions of dollars when its network was hacked, and customer information was stolen. Never let another company have something with unfettered access to your network. You have not vetted the employees, subcontractors, or security of the other company. When that company gets hacked, the ...


7

You can apply a filter to an interface in the interface: irb { unit 9 { family inet { address 40.224.224.14/29; filter input my-filter; } } } And then define that filter under firewall family inet: firewall { family inet { filter my-filter { term one { # filter ...


7

Let's look at what happens, shall we? 8.8.8.8 makes a good example, because at least from my location, I can reach it both with traceroute and ping. First let's try ping 8.8.8.8 and watch what happens: $ tcpdump -n host 8.8.8.8 or icmp 15:36:51.045994 IP 10.4.27.179 > 8.8.8.8: ICMP echo request, id 7215, seq 0, length 64 15:36:51.062458 IP 8.8.8.8 > ...


7

The IPv4 DF flag means that an intermediate host (router) cannot fragment the packet if necessary, and it would then need to drop the packet and can send an ICMP message stating that. RFC 791, Internet Protocol says: If the Don't Fragment flag (DF) bit is set, then internet fragmentation of this datagram is NOT permitted, although it may be discarded....


7

When the host starts up it has no knowledge of the network addresses or masks that it should use. The only way for it to communicate is via an IP broadcast (255.255.255.255) to the local network. The DHCP client initiates a broadcast request on UDP port 67. The client cannot use TCP because it does not have an IP address of its own, nor does it know the DHCP ...


7

The absolute limit is that each header can only appear once, except for the Destination Options which can come twice. In practice, you won't ever need all of them.


6

Because everyone is competing for airtime. It's the same reason traffic slows down on a highway as more cars travel on it. BTW 802.11 uses CDMA/CA That's collision avoidance, not collision detection (Ethernet).


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