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33

The MTU is the Maximum IP packet size for a given link. Packets bigger than the MTU is fragmented at the point where the lower MTU is found and reassembled further down the chain. If no fragmentation is wanted, either you have to check the MTU at each hop or use a helper protocol for that (Path MTU Discovery). Note that IPv6 does NOT support packet ...


24

In addition, MSS value is derived from the MTU. Consider that you have data of 2260 bytes to be sent to a remote device. If MTU is 1500, and we consider IP header + TCP header to be 40 bytes, then only 1460 bytes of data can be sent in the first IP packet. The remaining 800 bytes will be sent in the second IP packet. So, for MSS = 800, the MTU should be at ...


23

IP is a Layer 3 protocol. TCP/UDP are Layer 4 protocols. They each serve different purposes. Layer 3 is in charge of end to end delivery. Its sole function is adding whatever is necessary to a packet to get a packet from one host to another. Layer 4 is in charge of service-to-service delivery. Its sole function is to segregate data streams. Your computer ...


22

ARP is used by a host on a LAN to resolve a layer-3 address to a layer-2 address so that a frame can be built for the LAN. A router is just another host on a LAN, and it will need to resolve layer-3 addresses to layer-2 addresses, the same way a PC on a LAN does.


17

TCP/IP sockets establish an end-to-end connection through the network, between two specifically addressed end points. BGP uses TCP/IP to communicate between routers (any devices exchanging routing information.) The information exchanged is used by the BGP peers, to better choose the way they choose where to send, (aka, next-hop) packets that they need to ...


17

Yes, from the packet switching point-of-view, VXLAN is just a matter of sticking some encapsulation on top of an L2 frame: something that other protocols do as well. The real difference it makes is at the control and management layer. VXLAN evolved as a Data Center technology, so the ability to span a WAN is just an additional advantage, not the thing that ...


14

Routing protocols do not "achieve" L3 connectivity. They populate the routing (forwarding) table of the router with information learned from other routers. BGP is an "application" that runs over TCP/IP. In other words a BGP router uses TCP/IP to communicate with other BGP routers to exchange routing information. In order for BGP to work, you must ...


14

You need to understand the concept of layers. An application will send data to the Transport Layer. The Transport Layer protocol will encapsulate the data inside headers for the Transport Layer protocol, and pass those to the Network Layer. The Network Layer will encapsulate the datagrams it receives inside Network Layer headers, and those are called ...


13

Best practice wise - should I let the router or the ASA handle NAT (Overloading)? In the most general of design best practices NAT is performed between an inside and outside network. NAT overloading is generally performed at the edge when there is limited public IP address space. You can learn more about NAT overloading, also known as Port Address ...


12

NAT works at layer 3 because it is modifying the IP header. If you use PAT you could argue that it is working at layer 4 as well because it MIGHT change the source port of the packet in case it is not unique. Several internal addresses can be NATed to only one or a few external addresses by using a feature called Port Address Translation (PAT) which is also ...


12

Managed switches are in simple terms switches that can be "managed." Managed means that they can provide information/statistics about their operation and usually that they can be configured. While the vast majority of managed switches can be configured for IP (and this includes all the more capable devices with full feature sets), there are some that can be ...


12

The forwarding information base (FIB) is the actual information that a routing/switching device uses to choose the interface that a given packet will use for egress. For example, the FIB might be programmed such that a packet bound to a destination in 192.168.1.0/24 should be sent out of physical port ethernet1/2. There may actually be multiple FIB's on a ...


11

When you create 'interface vlan x' you are creating a brand new logical interface that happens to be automagically associated with the corresponding L2 vlan. When you put an IP address on 'interface vlan x' then you are simply giving that logical interface an IP that is on the same broadcast domain (or subnet or vlan or L2 domain or whatever terminology you ...


11

In general, layer-3 switches move packets faster (near line rate) because everything they do is in hardware. They tend to be cheaper and cheaper to operate (power, personnel, etc.) vs. a comparable router. This does come with significant limitations, however... reduced route table size no NAT no firewall and very limited security features limited routing ...


11

The original RFC for ICMP, RFC777 state that: ICMP, uses the basic support of IP as if it were a higher level protocol, however, ICMP is actually an integral part of IP, and must be implemented by every IP module. This statement is also present in RFC792 which obsoletes RFC777.


10

Every "header" has some sort of "Next Protocol" identification field. This is necessary because on the wire, the data is nothing but a string of 1's and 0's. The receiving endpoint must have a way of interpreting what the next bits refer to. If not for such a field which definitively indicates how to interpret the next set of 1's and 0's, there would be ...


10

In general, forwarding refers to a device sending a datagram to the next device in the path to the destination, switching refers to moving a datagram from one interface to another within a device, and routing refers to the process a layer-3 device uses to decide on what to do with a layer-3 packet. A host sending data to another host through an ethernet ...


10

Network address translation (NAT) is a feature of Router which is required for routing traffic. That is completely incorrect. NAT is a kludge (a clumsy, inefficient solution) designed to extend the life of IPv4 addressing until IPv6 is ubiquitous. NAT breaks the IP paradigm of end-to-end connectivity, and many things have problems with NAT. Routing works ...


10

Layer 3 (mostly IP) generally relies on the underlying layer-2 network (mostly Ethernet or Wi-Fi) for delivery. Just like a layer-2 network uses layer-1 links to actually move the bits. The difference in moving data at layer 1, 2 or 3 is the complexity of the devices. Layer-1 devices (repeaters) just copied bits - simple, yet inefficient and long obsolete. ...


9

it seems that routers decapsulate the frame on arrival, and encapsulate the packet in a frame in order to send it. Yes. A router must strip off the layer-2 frame in order to get to the layer-3 packet. The router then routes the packet to the next interface toward the destination, based on the layer-3 destination address. At the next interface, it must ...


9

I work at a large ISP and before at a different large ISP and both networks extensively use static routing. Mostly on the firewalls as they don’t want to run an IGP or BGP on the firewalls, but you can also find static routes on routers and even on end hosts. The implementation of OSPF on firewalls often was very buggy (and perhaps often still is) which is ...


9

As you point out, traditional DPI methods have limited ability to deal with encrypted traffic completely. They can still address encrypted traffic at a surface level at the very least, but it does tend to "cripple" their functionality in many ways. The new trend in security of this type is Network Traffic Analysis (NTA). Just as many companies are far less ...


8

There is two different things in term "Airplay". The first one is about service discovery and it's the way how devices capable of receiving Airplay streams announce to the network "Hey! I can receive Airplay!". It's done normally via service called Bonjour (at least Apple calls it so) or DNS-SD. It's using multicast and that's the point if someone is ...


8

If Layer-2 has a checksum, shouldn't this validation be enough? Why we are having checksum validation in different OSI Layers? Simply put, different layers of the OSI model have checksums so you can assign blame appropriately. Suppose there is a webserver running on some system (assume TCP port 80, i.e. OSI Layer 4) Suppose there is a software error ...


8

interface FastEthernet0 switchport switchport mode access switchport access vlan 1 ! interface GigabitEthernet0/1 switchport switchport mode access switchport access vlan 1 ! interface vlan 1 ip address 20.40.60.80 255.255.255.0 ! This should be the bare minimum configuration to get your scenario working, at least some IP connectivity. The ...


8

Add multiple aliases to my laptop NIC and do VLAN trunking on the port the NIC is connected to Your keywords here are "tagged VLAN". You might set up a switch port as a tagged member of all three VLANs and set up virtual interfaces using the VLAN tag identifiers in your Mac OS X instance, basically leaving you with three virtual interfaces in ...


8

The usual ping command uses ECHO REQUEST and ECHO REPLY, as you've seen. It does indeed locally keep track of sent time and matches with the incoming reply to determine the round trip time. TIMESTAMP and TIMESTAMP REPLY are pretty rare, and many sites simply don't answer, as many systems managers believe it to be a security issue, albeit minor. The ...


8

Most basic example of neighbor ports would be as you mentioned: "ports on two different switches (or routers) that are connected by a cable" You won't find a defined definition for this phrase because it will also depend on the context, for example when you are talking at a L3 from the OSI Layer, you might be going across several L2 ports, which each one ...


8

A single TCP segment is always converted to a single IP packet by adding IP header, which is in turn converted to a single Ethernet frame by adding Ethernet header (and footer). In other word, a datagram of an upper layer is converted to the payload of the datagram of the lower layer as a whole. That depends. For example, TCP receives a stream of ...


7

By "router leg" they mean a (directly) connected route (and use a strange way of putting it). What is a connected route compared to a static route? Connected route (router leg) A connected route is a route that points to an interface. For example if you configure 10.0.0.1/24 on (ethernet) interface Gi0/1 the directly connected route (the "router leg") is ...


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