Questions tagged [layer3]

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

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Routing end devices on VLANs through a layer 3 switch to the internet [closed]

I have a layer 3 switch which routes VLANs on different subnets between each other. Besides the trunk links for the VLAN interfaces, I have a router connected to another port on the layer 3 switch ...
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3answers
3k views

Juniper EX how to clear route forwarding table?

After layer 3 routing a large IPv6 assignment on an EX Juniper switch, the route forwarding table filled up and some entries corrupted or became otherwise invalid. We want to clear the whole table. ...
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5answers
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Inter VLAN routing working, but VLANs can't access Internet

i have a question/problem. i have a local router with default-gateway 192.168.3.254, now on my layer 3 switch 3560 i configure 3 vlans. vlan 10 - data /ip address 192.168.10.254 255.255.255.0 vlan ...
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4answers
89 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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3answers
115k views

What is the difference between MSS and MTU?

I'm confused as to the difference between maximum segment size and a maximum transmission unit. Can someone please explain in relation to layers 2 and 3? If I had a packet of 800 bytes in the ...
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1answer
40 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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3answers
2k views

Does a router send frames or packets?

Perhaps it's a novice question, but does a router send/receive frames? When I read about this subject, it seems that routers decapsulate the frame on arrival, and encapsulate the packet in a frame in ...
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1answer
57 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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6answers
856 views

Is a “LAN” a layer 2 or a layer 3 concept, in TCP/IP?

I think my question is purely theoretical and a matter of definitions; it derives from the fact that a L2-switch with VLAN capabilities is able to "create" different virtual LANs, and thus I am led to ...
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0answers
16 views

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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2answers
247 views

What is the advantage of Supervised Machine Learning over Deep Packet Inspection in Network Traffic Classification?

As per the definition of Deep Packet Inspection (DPI), it uses signatures for packet filtering. Supervised Machine Learning can help put a label on a packet which does not get identified by Deep ...
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1answer
40 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
43 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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1answer
63 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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2answers
38 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
23 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
32 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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3answers
389 views

Mgmt Vlan vs other SVI s

Think of a layer 3 switch. Assume that we have a management vlan and a mgmt vlan interface. And we have other svi's on the switch. The question is this. I know that mgmt vlan is for telnet/ssh, simply ...
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2answers
74 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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5answers
46k views

Intervlan routing using two Layer 3 Switches in Packet Tracer

I am having trouble when I am using two Layer 3 switches and two PCs to create a simple network for Inter Vlan routing, First of all have a look at this network, The configuration for PC1 is, IP: ...
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2answers
47 views

Am I correct to start thinking in terms of “ports” as “networks” or “devices”?

For the longest time, when I would configure a network device I would login to the GUI, and assign it an IP address. As I am getting into Cisco and their ISO model, I am seeing more and more of ...
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5answers
3k views

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page?

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page (same layer as IP) when the ICMP protocol data is a payload of the IP packet? This is the article on Wikipedia that states ...
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2answers
359 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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2answers
328 views

Packet transfer from one host to another

I was reading about how a packet is send from one host to another. I am confused about entries that will be made in layer-3 switch routing table. Does it contain the entries for layer two switches or ...
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3answers
4k views

What are the advantages of a firewall over a Layer-3 switch?

From my understanding, a Layer 3 switch can handle cross-communication between separate LANs and VLANs, as well as fine-tuned ACL control between VLANs. Despite this, I know a Layer 3 switch should ...
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3answers
2k views

How to configure static routing between two layer 3 switches?

I have two Cisco layer 3 switches. In switch 1, I created two vlans, 10.10.1.0/24 and 10.10.2.0/24. The connection is shown in the figure. PC 1 and PC 2 have static IP address (10.10.1.5 and 10.10.2....
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2answers
3k views

Inter VLAN with layer 2 and 3 switch

Is there a way to interconnect VLANs using this diagram? MLS0 has this configuration: interface FastEthernet0/1 switchport trunk encapsulation dot1q switchport mode trunk And SW0: interface ...
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1answer
92 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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4answers
6k views

Layer 3 Switch Routing vs Router on a Stick

CORE: Dell N4032 (6.3.0.18) Access: Dell N2048 (6.3.1.13) We are in the process of setting up a serviced office that will serve multiple businesses. Each "customer" will naturally be on their own ...
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4answers
244 views

Cisco cross-vlan routing

I have the following config snippets on a layer 3 switch: ip routing ! interface GigabitEthernet1/0/22 switchport access vlan 51 switchport mode access ! interface GigabitEthernet1/0/23 switchport ...
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5answers
185 views

Need of routers and IP addresses

I dont know if my research is enough or not but I could not find answers on the net. My question is why not use bridges instead of routers. We know bridges can connect two different networks. Using ...
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3answers
3k views

How to make two Cisco switches talk to each other

I have a layer 3 switch with multiple VLANs. I created a trunk port that connects to a layer 2 switch. I can now successfully access the layer 3 switch VLANs from an access port on the layer 2 ...
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2answers
168 views

Basic understanding of network operation

Assume two stations, A and B, are connected by two intermediate routers. A----R1-----R2----B Now, when A sends a packet to B, then the OSI model will come into the picture. Like, A's TCP layer will ...
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3answers
2k views

What is the proper switch configuration for the switch that is connected directly to ISP source?

The Question: What is the proper configuration for the L3 switch to be allowed to assign public IPs for the firewalls? I guess All I need is that the switch L3 act as a layer 2 switch...Right? ...
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2answers
340 views

Two Layer 3 Switches to one router

So I have a cisco 2811 router and 2 3560 switches Currently the router is connected to Core1 only, what i would like to do is use the other port on the router (fa0/1) to connect to Core 2. How do I ...
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2answers
333 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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3answers
4k views

At which layer does router operate?

I have studied from various sources that router is a layer 3 device. It does routing based on Network layer (layer 3) header, but I have a doubt. Network address translation (NAT) is a feature of ...
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2answers
2k views

Successful Intervlan Routing on a Layer 3 Switch, Unsuccessful IP Routing

Hello and thank you in advance for your help! I'm using Packet Tracer for testing purposes and I' m trying to implement a simple intervlan routing in a Layer 3 Switch (3560-24PS) and an IP Routing. ...
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5answers
623 views

Why is the IP layer aware of higher layers in the network stack?

In the IP packet header there is an 8-bit Protocol field (at offset 9) that holds the "next level protocol", with assigned numbers given in RFC 790. For example, TCP is 6. My question is, why is the ...
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4answers
8k views

Pinging a different vlan without routing

I have a layer 3 switch with two vlans 10 and 20. This is the only configuration i made on the switch: Switch(config)#vlan 10 Switch(config-vlan)#name IT Switch(config-vlan)#vlan 20 Switch(config-...
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2answers
88 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
451 views

VLAN on Layer 3 Cisco C3560

I am looking to get a layer 3 Cisco switch and I know how to setup vlans, I will have the internet connection coming in from the pfsense router on port 1 and then vlan 10 on port 10 and vlan 20 on ...
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4answers
475 views

InterVLAN Routing Plan

My network currently has 7 VLANs (2 user, 1 voice, 1 server, 2 wireless, and 1 for our networked A/V equipment). All of our switches are layer 3 Cisco Catalysts. However, we currently have a router-on-...
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2answers
432 views

INTER-VLAN Routing with different Internet Access for each vlan

I have a situation that needs some clarification. I have three sites (1,2,3). The core switch do Inter-vlan routing. Site 1 and 2 must access the internet via ISP1, while site 3 will access internet ...
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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
3k views

Router vs VLAN in networking?

Why do we need Routers at all when we have VLAN ? Vlan breaks the broadcast domain. Vlan along with the use of SVI can be used for routing. So why do we need routers for in networking ?
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3answers
289 views

1 Layer 3 Switch, 2 Vlans, 2 Subnets, and an Unmanaged Switch

Is it possible to for a device with the ip address 192.168.0.1 and Vlan 100 to communicate with an other device with the ip address 192.168.1.1 and Vlan 200 with the following architectures Senario 1:...
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3answers
4k views

Connecting Layer 2 switchport to layer 3 port

I have a config that I am trying to bring up, and in my mind it should work, but perhaps I am missing something. The idea is that one end of the link is a layer 3 interface on a router. The other end ...
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2answers
1k views

Firewall on a stick for Intranet and static routing

I have a question about possible problems that can occur with this network design. If I have an intranet with a firewall on a stick design, multiple switches with layer 2+, is this setup fine? or ...
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3answers
428 views

Is static routing used in large networks?

I'm a beginner in networking stuff and just wondered if Static Routing has any use in large networks ? How about small ones ? In which cases we prefer to use static over dynamic routing ? I searched ...

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