Questions tagged [layer3]

For questions about the OSI layer-3 (network layer).

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Does a router work both on Layer 2 and Layer 3? [duplicate]

According to TCP/IP model router works at Layer 3. But when data has to be transmitted to different network it is based on IP address but hop-to-hop transmission is based on MAC address. That means ...
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2answers
76 views

What is the minimum MTU of IPv4 68 bytes or 576 bytes?

I read that 68 bytes is the minimum size of IPv4 datagram every device must be able to forward without further fragmentation. 576 bytes is the minimum size of IPv4 datagram every device has to be able ...
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2answers
381 views

Why the two connected routers via PPP doesn't use ARP but ethernet use 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, ...
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25 views

Why loop back address never cross data link layer and physical layer? [duplicate]

Suppose I have one source ip address 101.101.25.36 whose destination address is 1270.0.0.1. That means destination ip is loop back address. Whenever packet has loop back address as destination address ...
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1answer
108 views

If the probability of frame being lost is P. Then, calculate the mean no. of transmission for the frame to make it success [closed]

Here the probability of frame being lost is P. So the probability of frame reaching safely would be (1-P). Now lets consider that the frame will reach safely in K-th transmission. That means that the ...
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3answers
210 views

Why does OSPF use flooding despite using multicast?

We know that flooding is only possible in layer2 switch. But in OSPF router in layer3 uses flooding with multicasting. Suppose we have one router in OSPF uses multicast address 225.0.0.9. If router ...
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2answers
80 views

How in Distance vector routing one router communicates adjacent router through broadcast address and OSPF uses unicast with another?

In distance vector routing algorithm one router can communicates(shared the routing table) with adjacent router by broadcasting message which are in same subnet. OSPF uses flooding to unicast message ...
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1answer
86 views

Are IPv4 type of service and IPv6 traffic class equivalent to each other or is traffic class IPv6 specific? [duplicate]

IPv6 has a traffic class field. According to the specification it is an IPv6 length, out of which first 6 bits are called code point or differential services code point (DSCP) and the last 2 bits are ...
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1answer
41 views

How UDP checksum get IP address to make pseudo header in transport layer?

We know that UDP checksum's pseudo header contains the most important parts of the IP header, that is, source and destination address, protocol number and data length. I hope that the concept of IP ...
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2answers
94 views

Why router can't be used for converting different model of network but gateway can do this?

We know that Router can't be used for converting different model (e.g OSI model to TCP/IP or TCP/IP model to OSI) of network. It isn't a multiprotocol converter. But gateway is a highly sophisticated ...
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1answer
74 views

Does a router have multiple DLLs inside?

I came across a practice question of true/false answer type . The statement is: "A router has single network layer that will interact with 2 Data link layers" . Ans:True (no explanation ...
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1answer
43 views

How Pruning avoids loops in Protocol Independent Mulitcast (PIM- SM)?

I can not think of a scenario, how pruning avoid loops in PIM-SM when a router joins a SPT. I understood that it avoids duplicate messages, but how it avoids loops? I want a scenario where the router ...
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4answers
103 views

If router is a layer 3 device how can it have an application interface (GUI)?

It is said that layer 3 devices such as routers do not have an application layer. But whenever I want to configure my home router I punch in the IP address and open up its graphical user interface. ...
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1answer
144 views

Cannot Create Subinterface on C3650 L3 Switch

We have WS-C3650-24TS Catalyst L3 switch. I am trying to create a sub-interface on the ports but cannot make it work as the following error shows. Is there something I'm missing? Sorry, newbie here.
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MPLS provider A L3VPN to MPLS provider B migration

i have a Datacenter infraestructure with a mpls of SP A, and i would like to migrate to another wan line of a different SP B. Mpls current circuit is providing L3 VPN service, one VPN per remote site. ...
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1answer
108 views

ICMP packets are being dropped while pinging

I am pinging from one of the Juniper L3 interfaces to another with a rapid ping count of 10000 packets. It's a direct 100G optical connection and I am seeing 10-15 packets being dropped by the end of ...
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2answers
46 views

How to configure static routing when there are two routers between the source and destination network?

How can i perform static routing from router A to reach 192.168.1.0/30 network in the below diagram(please don't ask why do i need two routers between them). All the example of static routing i have ...
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2answers
55 views

Proxy-ARP when the destination device is connected to the same layer-2 switch, but belongs to a different subnet

I have recently learned about Proxy-ARP and am slightly confused about what would happen in the following scenario. Let's say I have two host devices A (IP: 10.0.0.10/24) and B (IP: 10.0.1.10/24) that ...
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1answer
30 views

Routing switches at core and distribution

My employer has your standard 3 layer architecture, however they want both core and distribution routing and switching. This is so that some networks are routed, and some use only layer 2 between ...
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2answers
34 views

Tagging a Vlan across routers

I'm usually against tagging a VLAN across a router, as to not incur issues with spanning tree. My company is asking the following PLC --Vlan72-- SwitchA --RouterA---CoreRouter---RouterB---...
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1answer
95 views

How does Network Layer behave when client received a unicast DHCP offer?

I went through various stack exchange post to understand the concept of DHCP offer when it comes as a unicast to client from the DHCP server. A server can send a unicast DHCP offer since it knows the ...
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1answer
165 views

What is the impact of "no switchport" with "no ip address"?

I've a monitoring tool named Spectrum from CA Click. It automatically forms links between devices by check their configuration, and etc. Recently a change was made on my switch by a regional and the ...
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2answers
107 views

Link failure detection between 2 routers

When 2 routers are linked directly together with eBGP between them, how is a link failure detected ? With the BGP timers ? Or faster with some sort of L1 tool? For instance, assume we have the ...
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2answers
1k views

How do I know the switch is layer 2 or layer 3?

Is it possible to find the switch is Layer3 or Layer2 in (Switch)CLI? Is there any command to check whether the switch Layer(Layer 3 or 2) in CLI?
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2answers
67 views

How does an L3 Supported Switch differentiate L2/L3 Packets?

I had a managed or layer 3 supported switch (it can process both layer 2 and layer 3 packets). Now a packet from a connected host comes to it, sending traffic. How does the switch decide to process it ...
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Switch vs. Router and sequence of OSI Model [duplicate]

As I understand it: A switch (layer 2) seems to define a LAN and a router (layer 3) enables communication between distant LANs. A device on a LAN will give it's MAC address to the switch upon ...
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2answers
67 views

Some extra clarification regarding VLANs and SVI

Good afternoon guys, I've got a question regarding VLANs and SVIs. First of all, I know some concepts about VLANs, and I've been in the IT field for a while. But this one is a bit confusing for me. ...
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3answers
230 views

Why is in all arp table snmp oids an interface index before the ip number?

When I want to get arp information about a single ip number or subnet, I have to snmpwalk the whole arp table, as some oid architects had the "great" idea to always insert an interface index ...
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2answers
95 views

When traffic is intiàted from pc is ANDing process or ARP process start working first

When traffic is initiated from desktop which process starts first; the ARP process or ANDing process?
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1answer
2k views

intervlan routing with PfSense

I Need some guidance on getting my lab networking configured. Any support is appreciated. My Lab consists of: 2 cisco switches: 2960s(access layer 2) and 3750X(ip routing/layer 3) Xenserver with ...
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2answers
219 views

Connecting switches together

I have L2 switches which will be daisy chained together (yes I know, daisy chaining isn't great, but anyway..) The L2 switches will then link to a L3 switch. Both the L2 and L3 switches have x4 10GbE ...
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3answers
943 views

Minimum MTU size on Ethernet and minimum Ethernet frame size

I am a bit confused about the understanding of the relationship between minimum MTU of MTU and minimum Ethernet frame size. We know that the maximum MTU of Ethernet is 1500 Bytes which makes the ...
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2answers
77 views

Layer 2 managed switch and layer 3 switch

If you have layer 2 managed switches which have VLAN's on them, do you still need a layer 3 switch/router?
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2answers
39 views

What is the need for the NEXT HOP coloumn in the routing table when we already mention the OUTGOING INTERFACE in another coloumn?

If the OUTGOING INTERFACE is already mentioned in the routing table, it is natural that the next hop will necessarily be the router attached to the outgoing interface. Then why is there a separate ...
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0answers
30 views

network cutover for remote site from L2 to L3 over IPSec tunnel

I have been trying to cutover one of our remote sites (A) to the new ISP we have purchased. The existing setup is utilizing L2 through another remote site (B) and coming back to the main campus. The ...
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2answers
282 views

Are all packets addressed with the MAC address of the router as they leave the machine?

In the Comptia Network+ All in One, it is said that most home routers have a switch built into them. It is also said that the first thing the router does is strip off any layer two information present ...
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0answers
14 views

Basic Subletting 10.239.142.216/11 [duplicate]

First time poster (kindly don't eat me alive) i was using https://subnetipv4.com/ to acid test my subletting skill i got 9/10 correct this is the chosen one that broke my streak as you can see i ...
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1answer
133 views

Why does the Layer 3 switch drop the ping packet?

I am trying to ping from PC2 (not PC1, there's typo in the picture) to the router's int g0/0, but the packet is dropped at the L3 switch which is along the path. I have tried setting a default static ...
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1answer
89 views

what were the classless routing protocols used with VLSM when it was first introduced?

Since VSLM is supported only by classless routing protocols, if VSLM was introduced in 1987(RFC 1009) and all classless protocol(RIPv2 developed in 1993 , OSPF standardized in 1989 RFC 1131 ) cited ...
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2answers
434 views

Vlan vs. Subnet Broadcast Domain

It is my understanding that Vlans separate broadcast domains, but I often see people say, "subnets define a broadcast domain" as well. Is it correct to say, "Vlans define a L2 broadcast domain, and ...
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1answer
243 views

How does a 802.11 (wifi) frame identify the payload's layer 3 protocol?

My understanding is that the 802.11 frame header is an equivalent of ether header. In the ether header, there is an EtherType field that identifies the payload protocol, such as IPv4/IPv6/ARP etc. ...
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3answers
1k views

Clarification on when routers encapsulate and decapsulate packets

I'm an application developer working on getting a working knowledge of network engineering, so basically a newbie. I've been trying to figure out exactly when routers decapsulate frames into packets ...
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2answers
513 views

How do computers send switches packets, if switches don't have IP or MAC addresses?

I am new to networking, so please excuse me if I am saying stupid stuff. From my understanding, PCs are sending packets to switches, which then decide which physical port to forward that packet to. ...
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1answer
349 views

Why Classful addressing is not in use if we can subnet them?

So, Let's think that organization needs 5000 IP addresses. Giving 20 C Class IP addresses will cause of adding 20 entries for ISP router. That's problem. We could give Class B IP address, but that ...
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1answer
106 views

Is an IP broadcast always a layer 2 broadcast also

On my PC I see 255.255.255.255 in ARP with MAC FF:FF:FF:FF:FF:FF, so I'm assuming that in most cases the L3 broadcast is also encapsulated into an L2 broadcast frame, but is this standardized? For a ...
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1answer
231 views

Question about MTUs vs maximum frame sizes - what is their difference?

I am currently studying networking at university and I have a question about MTUs and maximum frame sizes. What is the difference between the MTU and the maximum frame size? This Wikipedia article ...
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2answers
812 views

Confusion about data fragmentation/MTUs - why was it introduced in the first place?

I am currently studying networking as a part of my bachelors and I am a bit confused about why fragmentation/MTUs are necessary. In my lecture slides, it only says "Fragmenting if necessary" under the ...
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2answers
193 views

Question about the destination IP inside an IPv4 packet

I'm reading about link and network layers for the first time and I'm trying to put the pieces together to understand how they work together. My question may not have to do with the link layer but I'm ...
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2answers
411 views

Unable to ping between router and routed port on L3 switch. Why?

I've got an old Cisco 2811 connected to an old Cisco 4948 L3 Switch. I'm trying to teach myself a little more about L3 Switch implementation. All I'm trying to do at this point is get the router and ...
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2answers
88 views

Can Northbound interfaces (REST API) in a Software Defined Network (SDN) be used to manipulate QoS parameters?

I am working on a project involving Quality of Service (QoS) manipulation in Software Defined Networks (SDNs). I know that the following parameters affect the QoS in an SDN: Time information (inter-...

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