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Questions tagged [layer3]

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

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2
votes
1answer
350 views

How can a telecommunications carrier convert his layer 3 transmission network to layer 2 at client site?

Ok, my company has three telco providers, each telco provides data links from the central site to different remote sites. Telco provider 'A' provides layer 2 "dedicated" fiber optic links from the ...
3
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4answers
1k views

Should I receive an ARP reply from a host that is logically on a different subnet but is connected to my host via a hub?

Host A: 128.238.66.100/16 Host B: 128.238.67.100/24 The hosts are connected to the same hub and nothing else is connected to that hub. The routing and ARP tables of both hosts are empty. Host A ...
2
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2answers
8k views

Routing the same subnet in two locations / gateways?

In my current topology, I have two locations linked by a trunk. Everything on one side of the trunk is Site A, everything on the other is Site B In the example above, for 10.0.200.4 to talk to 10.0....
5
votes
3answers
423 views

Why use 'switching' term for packet switching

On a packet switching network, a router is required to route packets to different networks. Why does packet switching uses the term 'switching' when a packet is a term for a layer 3 PDU and ...
-2
votes
1answer
97 views

L3 switch - All L3 processing offloaded to card?

On a Cisco 3560 switch, are all L3 processing offloaded to card instead of normal CPU?
8
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3answers
29k views

Access Multiple VLANs from One Computer

I inherited a bit of mess and am preparing to redo our IP addressing scheme and also split our network into multiple VLANs. Possibly something like: 10.1.10.0/24 VLAN 10 VOIP 10.1.20.0/24 VLAN 20 ...
5
votes
2answers
537 views

Network topology suggestions?

Looking for guidance on network topology changes. Currently our network has 2 different stacks of switches running in layer 2. These switches then connect to a stack of layer 3 switches to do internal ...
5
votes
1answer
577 views

Cisco Router Multiple Interfaces in the Same Broadcast Domain

I have a Cisco 3945E with two EtherSwitch modules (gi 1/0, gi 2/0) and a UCSE (ucse 4/0) server installed in it. The short of it is i'd like to trunk VLANs to the two EtherSwitch modules, and place ...
3
votes
2answers
5k views

How does IS-IS carry IP routes?

IS-IS runs natively on layer 2 of the OSI reference model. How will the routing be done in that? My doubt is that layer 3 has the ability to do the routing. But, ISIS does not run in layer 3 rather ...
3
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2answers
3k views

Do MPLS LSRs require a Layer 3 IP routing protocol?

Recently I've been trying to get my head around MPLS, it's a part of the project we're doing. During one of our meetings one of the participant ask a question: Since LSRs doesn't check IP routing ...
4
votes
1answer
213 views

Hub-Spoke topology — L3 Links use multiple /30s vs single /24 shared?

I wanted to ask the community their thoguhts on the pros and cons of this scenario. I have a few L3 switches with their own independent VLANS connecting to a a set of stacked switches over a port-...
1
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2answers
7k views

How to assign a static IP to a Cisco Layer 3 switch in order to connect using SSH?

The steps of this manual have been executed in order to configure SSH. Once SSH has been configured, how to access the switch from a computer using SSH? The following steps have been executed in ...
4
votes
3answers
992 views

When are MAC addresses used instead of IP addresses in the OSI model?

Okay, so I'm studying for the Network+ exam, and I've gone over the OSI model about a million times, and I understand most of it fairly well, and my studies are coming along fine. However, there is ...
3
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2answers
3k views

Layer 3 Switching in Packet Tracer not working

I am studying for ICND1 through CBTNuggets, I recently watched videos on how to interact between different vlans using separate interfaces, sub-interfaces and Layer 3 Switching. The first two worked ...
4
votes
3answers
958 views

When is a layer 3 switch more appropriate than a router in a branch office?

It seems that as time passes, vendors have added almost all the features of a router to a layer 3 switch. For branch office deployments, how do other people who design networks choose between ...
4
votes
2answers
1k views

Difference between router leg and static routes

I am looking a L2/L3 switch spec. which says it supports 256 Router Legs and maximum of 32 Static routes. Can somebody explain with an example, what is the difference between router leg and static ...
6
votes
1answer
992 views

Connect Multiple VLANs which reside on same L3 Switch

Introduction The steps described in this manual have been applied in order to enable the connection between multiple VLANs which reside on the same switch. Two VLANs have been configured. VLAN 1: ...
33
votes
3answers
96k 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 ...
1
vote
2answers
1k views

Routing Between Cisco 4507R+E Layer 3 Switch & UTM Firewall Fortigate

Please Help me. I have a Cisco Catalyst 4507R+E and UTM Firewall Fortigate and I Created VLANS on Catalyst and the main VLAN port Which Play IP Route between All VLANs can not connectet to the UTM ...
13
votes
6answers
10k views

How does BGP work over TCP?

As far as I know we are using routing protocols to achieve Layer 3 connectivity, I am confused with the fact that BGP works over TCP which is L4. How can L4/TCP be established without prior L3 ...
17
votes
6answers
55k views

What, exactly, is required to make Airplay work across VLANs? [closed]

It seems like AirPlay works out-of-the-box, vaguely speaking, only within a LAN. It's not clear to me exactly why, but it looks like at least discovery relies on broadcasts. Wikipedia states that ...
1
vote
1answer
4k views

Routing throughput of an L3 switch

The Cisco SG300-10 says its forwarding rate is 14.88Mpps with 64 byte packets. I estimated this to be ~ 7 Gb/s. Does this mean that up to 7 computers can transfer data across VLANs at full 1 Gb/s ...
4
votes
1answer
6k views

Why are there checksums for different OSI layers?

Can anyone clarify the question "why we need checksum in both layer-2 and layer-3 of OSI layer", Layer-2 would encapsulate the rest of OSI layers into a single unit. If Layer-2 has a checksum, ...
4
votes
3answers
545 views

'interface vlanX' or 'interface loopbackX'

VLANs are a layer 2 concept. We can all agree on that but why, then, do we use the 'interface vlanX' to allow routing on a switch. If we want to setup a default gateway for VLAN X on a Layer 3 switch ...
3
votes
1answer
2k views

Routing of 2 Gateways via a Layer 2 Switch

Please refer to the network diagram below, it is a very simplified version of an actual network installation. The Router has 3 Vlans, OSPF has been configured and all the 3 vlans have been added to ...
5
votes
1answer
1k views

Is Layer 3 web auth with Layer 2 PSK more secure?

I have configured a Cisco WLC to authenticate users using External Web Authentication at Layer 3. Are client wifi connections more resilient against eavesdroppers with a pre-shared key at Layer 2 ...
8
votes
2answers
9k views

Cisco ASA Routing Issue

I am working on a lab right now and am having some issues with ASA routing. Here is the current network topology: Currently if I login to the console on the ASA or Router I can get outside to the ...
8
votes
3answers
23k views

What layer of the OSI model does NAT work?

Simple question and the answer is layer 3 of course, but can we say that PAT is working on layer 4 also because it deals with port numbers which is a layer 4 function? Or is it only a layer 3 ...
5
votes
1answer
1k views

Layer 3 network, multiple internet connections

I'm using a Procurve 5406zl (J8697A) layer 3 switch with multiple vlans: VLANs: v10 Main Network 10.1.4.1 v12 Wireless 10.1.8.1 v13 Restricted Wireless 10.0.0.1 v14 Tech 192.168.7.1 v50 Internet 192....