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Questions tagged [layer3]

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

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How Does A Layer 2 Switch Differentiate Between Different Networks?

I know that different IP-based networks can be connected to the same layer-2 switch. and I know each network's nodes can communicate just fine, however, no normal traffic can occur between two nodes ...
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0 answers
7 views

How IP packet's payload bigger than the whole former PDU (segment)? [duplicate]

As far as I know: File is too big ---> Fourth layer (TCP or UDP) divide it to a multiple segments ---> Then each segment encapsulated separately into a packet. What means if I have 10 segments, ...
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1 vote
1 answer
41 views

ICMP codes in response to ICMP traffic, not UDP/TCP

I am trying to wrap my head around a concept and I am having some trouble. If I ping 8.8.8.8, 10.8.1.1 replies to me "Destination port unreachable". Ping uses ICMP, so it does not have a '...
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1 vote
1 answer
93 views

Ospf multicasting with two different group

Suppose I have one ospf network where two multicast group exists. And some routers is ospf which belongs to one group or multiple group (Like: routers E, H) and router is layer3 router (Like: ...
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2 votes
1 answer
61 views

Custom option in IP header

I would like to add (or piggyback on an existing not used) a custom option to the IP header. I've full control of the IP stack at both end points, but I've no control on all the hops in the route (...
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  • 123
0 votes
1 answer
38 views

Fragments taking different routes?

I have trouble understanding why sometimes it occurs that during IP fragmentation certain fragments take different routes. I was following this the second example: https://www.gatevidyalay.com/ip-...
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1 vote
1 answer
99 views

How n level come to know the n+1 level contents?

Suppose in application layer is running some application. And application has respective source port number and destination port number. And know that n layer has no authentication to know about n+1 ...
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0 votes
1 answer
28 views

Actually ICMP message makes layer3 reliable?

We know that ICMP is connectionless because it does not require hosts to handshake before establishing a connection. But when packets gets dropped in between route then respective router informs the ...
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1 vote
1 answer
62 views

Router could get packet of size more than 1500 bytes?

Suppose transport layer get the segment 4000 bytes from application layer at sender site. But we know maximum MTU in layer2(Ethernet) is 1500 bytes. My question is so fragmentation is happening at ...
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3 votes
2 answers
167 views

Time taken to complete a routing table update and possible interruption

I am wondering if a routing/forwarding table update at a switching node (e.x., a switch or layer-3 router) can cause momentary packet drop or increased delay for a data stream that will traverse this ...
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  • 35
0 votes
1 answer
68 views

Understand router Ip address and Mac address, Switch Mac address

Scenario:1 Suppose external Router R1 has interface a connected with interface b of the site Router R2. And Router R1 using IP address 80.0.0.0/8 for a. Router R2 has 4 subnets 80.0.0.0/10, 80.64.0....
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2 votes
1 answer
65 views

Which ranges of IPv6 and IPv4 do requests to the local network and the host?

I'm looking for the range of IP address that is bound to the local network or the host itself. So far for IPv4 I found: 10.0.0.0 - 10.255.255.255 172.16.0.0 - 172.31.255.255 192.168.0.0 - 192.168.255....
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1 vote
1 answer
24 views

Does a Transparent Firewall need a Default gateway if directly connected to a layer 3 device that is actively performing routing?

Good folks of the Network Engineering stack! I have a question that I assume most people could answer in their sleep. To better illustrate my question, I've provided a sketch of my network below. In ...
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  • 13
0 votes
2 answers
165 views

Acknowledgement, retransmission of layer2 is actually belongs to layer4?

I followed from this question understand that only transport layer responsible for acknowledgement. But I have read on book stop and wait, GBN, SR protocols uses acknowledgement, retransmission in ...
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0 votes
2 answers
122 views

What is responsibility of different layers of OSI model and intermediate devices between sender and receiver when data packets are lost/corrupted?

Suppose sender sending some data to receiver and there are 3 routers between them. R1, R2, R3 are routers. Now sender starts sending data packet D through it's AL, TL, N/W L, DLL,PL to router R1 ...
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1 vote
2 answers
75 views

Does a gateway always have to be on the same subnet as the host IP address? [closed]

The obvious answer is yes, I suppose, but my VPS provider doesn't seem to agree. I've just uploaded a Ubuntu 20.04 instance, and the provider is telling me: IP address: 77.xxx.yyy.zzz/32 Gateway: 10....
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  • 157
1 vote
2 answers
48 views

Best way to configure layer 2 daisy chain with 2 layer 3 switches/gateways at either end?

I would like to implement a linear daisy chain for the purpose of transmitting internet over a considerable distance. One motivation behind the use of a linear daisy chain for this problem is that ...
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  • 13
0 votes
2 answers
113 views

Could we use private IP address as directed broadcast address?

We know that private IP addresses ranges of class A, class B, class C are 10.0.0.0-10.0.0.255, 172.16.0.0-172.16.255.255, 192.168.0.0-192.168.255.255 respectively. My first questions is that first and ...
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1 vote
1 answer
61 views

Layer 3 switch as access switch

Is it possible to have Layer 3 switches at access level (meaning the PCs are connected to it) if multiple VLANs are spread out accross multiple switches? For example, VLAN 10 is present at SW1 and SW2....
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1 vote
0 answers
31 views

Logs on my Cisco ASA show the public gateway (ISP router) is pinging the internal network, how? [closed]

Im (remotely) working with an issue where the network has intermittent drops. i suspect possible routing loop, but havent confirmed that yet. In the logs of our Cisco ASA 5506, i see that the public ...
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  • 21
0 votes
1 answer
96 views

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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  • 11
1 vote
2 answers
473 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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3 votes
2 answers
454 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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2 votes
3 answers
328 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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-1 votes
2 answers
122 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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1 vote
1 answer
105 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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0 votes
1 answer
76 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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0 votes
2 answers
110 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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0 votes
1 answer
83 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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1 vote
1 answer
47 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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1 vote
4 answers
132 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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0 votes
1 answer
298 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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0 votes
1 answer
308 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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0 votes
2 answers
53 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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1 vote
2 answers
79 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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0 votes
1 answer
40 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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0 votes
2 answers
51 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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1 vote
1 answer
110 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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2 votes
1 answer
326 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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0 votes
2 answers
184 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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  • 107
6 votes
2 answers
2k 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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  • 125
1 vote
2 answers
97 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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0 votes
0 answers
27 views

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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0 votes
2 answers
98 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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1 vote
3 answers
293 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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1 vote
2 answers
122 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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0 votes
1 answer
3k 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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0 votes
2 answers
332 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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  • 495
1 vote
3 answers
1k 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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0 votes
2 answers
93 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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