Questions tagged [layer3]

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

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How to implement Layer 3 (OSPF, IS-IS) link redundancy?

I think this kind of topic may be a course basic, but I'm still have a lot of technical doubts on how to implement redundant links on Layer 3, for example: -In order to use dual homing for a remote ...
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1answer
1k views

SD-WAN vs MPLS VPN

Citing wikipedia on MPLS VPN There are three types of MPLS VPNs deployed in networks today: 1. Point-to-point (Pseudowire) 2. Layer 2 (VPLS) 3. Layer 3 (VPRN) I am confused about the difference ...
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2answers
371 views

CGN and its advantages

I have been reading about CGN. Though similar to NAT it is used by service providers to route traffic without the need for the a public IP address. But when the packet leaves the ISP to the public ...
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2answers
347 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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1answer
57 views

Catalyst InterVLAN Routing w/ Failover ASAs

I currently have interVLAN routing configured on my Catalyst 3750. My gateway of last resort is my ASA firewall. The switch reaches the firewall through a layer 3 port. The port is configured as ...
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3answers
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How does a router a layer 3 device translate port address in PAT, as it is a layer 3 device?

While I was reading about PAT i.e Port Address Translation.The router was configured to translate all the private IP addresses to one single public IP.Since router is a layer-3 device, it can do that ...
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3answers
9k views

How to trunk VLANs over Layer 3 EtherChannel?

I am trying to setup a network that includes an EtherChannel link between two Cisco Layer 3 switches (Catalyst 3750). I am using a collapsed core hierarchical network. The picture above is my ...
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2answers
439 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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1answer
83 views

How to extend ports with L3 switch or other device? [closed]

I am a software engineer and no one in my team is familiar with network setup. My team recently bought 20 PCs for test our software but we only have 2 ports left in the room. And I have suddenly come ...
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2answers
4k 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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208 views

Is it possible to have a single port serve a layer 2 and 3 link simultaneously?

We are moving to a new L2 fiber network and i'm having trouble figuring out how to connect the DR. We are using a spoke and hub topology, with HQ as the hub. The branch locations all have unique ...
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2answers
11k views

VXLAN vs VLAN over layer 3

I read that one of the benefits of VXLAN over VLAN is that it can spawn across WAN and multiple layer 3 networks by creating overlay layer 2 networks. However AFAIN VLAN can also do the same using ...
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2answers
705 views

Does a router divide a LAN into two seperate LANs, or a single LAN with two subnets?

The figure below is part of a networking homework question. The question asks about the source/destination IP and MAC addresses of frames sent throughout the system. My question doesn't touch on that ...
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1answer
92 views

Default Action in SDN Controller

In legacy IPv4 networks there exists a default route concept for routers where a router does not need to know exact destination of IP packet. Is there a default action concept for SDN switches? Let ...
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1answer
141 views

L3 routing between switches with some VLAN's trunked

During a migration various L2 equipment will be replaced with all Cisco L3 switches and over time traffic migrated to routed subnets instead of trunked. There are two straightforward approaches that ...
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4answers
487 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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1answer
67 views

Do packets take the same amount of time when they are within the MTU?

Without considering application processing or deep packet inspection, do packets that do not fragment all travel through the network at the same speed? For example, if there is a network with an MTU ...
2
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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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1answer
8k views

What's the difference between port number and protocol number?

Can someone explain it clearly. I know that port numbers are used by applications to differentiate which services you have requested, and routing protocols use protocol numbers in TCP header.
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1answer
59 views

RVIs and routing out of firewall

I have managed to configure a number of EX3300 switches (using virtual chassis) with vlans and the appropriate layer-3 configurations for RVIs. I can get the traffic to flow internally on the ...
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4answers
2k views

Network service that is both connected and connectionless

I'm reading through Kuross "Computer Networking, a Top Down Approach". In the chapter about the network layer, they mention "In all major computer network architectures to date (Internet, ATM, ...
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4answers
9k 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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1answer
294 views

Why does a layer 3 hop use vrrp secondary on nexus 6001

I have a nexus N5K-C5672UP as core layer 3 for our VLAN's. VLAN 601 on core 2 is secondary vrrp: core 02: core02# show vrrp Interface VR IpVersion Pri Time Pre State VR IP addr ---------------...
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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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1answer
677 views

Cannot access Internet from VLANs on an HP layer 2 and layer 3 switch

I have got an HP switch, layer 2 and layer 3 capable. I created some VLANs. I have an ADSL router on VLAN 1 with the IP address 192.168.1.2. From VLAN 1, I can access Internet, but from the other ...
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1answer
232 views

VSS for layer 3 only 6500

I have 2 6500 at the core, that have only L3 links to the DC and the campus. I'd like to set VSS but I'm wondering if it's possible in such scenario. It uses OSPF for the routing. I'll have the ...
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3answers
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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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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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1answer
55 views

Host behavior with mask +1 and -1

Let's suppose I have a configuration: host: 192.168.1.145/25 gateway: 192.168.1.129 network: 192.168.1.128/25 broadcast: 192.168.1.255 What happens if I add +1 bit and remove -1 bit to the mask? 1) ...
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1answer
511 views

How do we find the host name name by using mac address,VLAN or IP address on Layer3 switch [closed]

have quick question How do we find the host name name by using mac address,VLAN or IP address on Layer3 switch . i pull up the vlan and mac address using my IP by i couldn't figure it out the host ...
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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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3answers
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In IPv4 does the identification field in a TCP packet change for fragmented packets?

If a TCP packet is fragmented then would the identification field of the header stay the same for all of the fragmented packets, or would it increment by 1 so that the receiver would know what packet ...
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4answers
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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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2answers
6k views

Designing a redundant switching infrastructure

Ultimately I've been tasked with the installation of a serviced office with upwards of 1000 staff, potentially being spread across 50+ VLANs. The hardware bought was out of my hands, but it's fairly ...
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1answer
1k views

HSRP on switch interfaces

As part of my internship/thesis, I am looking to implement HSRP in a network. The network has 2 separate locations that are connected with a fibre cable (layer 3 to layer 3). Each layer 3 (Cisco ...
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3answers
1k views

Need for network layer

I was reading about the 'IP' in TCP/IP. Most of its functions seem to be for connecting different (types of) networks. Does this mean that network layer is not required for communication between ...
2
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1answer
697 views

VLAN vs Subnet in switch

For VLAN communication we need a layer 3 device. For internetwork communication, we also need a layer 3 device. Then why did concept of VLAN emerge?
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2answers
92 views

Lab: I have a ISR with layer 2 ports that i need to connect to a 6500 layer 3 routed port

on my network vlan1 is to be non routed management traffic between switches etc. vlan2 is general network vlan3 is wifi vlan4 is a point to point between routed interfaces vlan5 for servers. ...
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1answer
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Inter-VLAN Routing with VTP Server and Clients in Packet Tracer

I am new to the networking world and am attempting my first few projects in Packet Tracer. The first few were easy but I've gotten to a road block. My goal is to have three separate VLANs with at ...
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5answers
186 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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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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3answers
5k views

Does a switch understand packets? If yes, what is the frame terminology for?

I was a little confused between packet and frame. The confusion was based on, if a switch is a layer 2 device, how does it reads a packet from a layer 3 device, and where is the 'frame' thing which is ...
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3answers
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spanning tree at layer 3

we want to prevent loops in the network be it LAN or WAN. However for layer 2 LAN networks STP is used to prevent looping switches. However at layer 3 TTL field is used. why not use STP for layer 3 ...
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2answers
2k views

ARP spoofing in different VLAN

I want to know if I'm protected for ARP spoofing. In my network, all PCs, printers, phones and servers are in distinct VLANs. I got a layer 3 switch for servers, which handles routing between these ...
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2answers
386 views

Understanding VLAN tagging

Let's say we have 4 machines connected to a layer 2, managed switch which is connected to a layer 3 switch. Say that 1.2.3.0/24 is routed to the layer 3 switch. Our goal is to have 1.2.3.0-63 usable ...
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4answers
245 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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1answer
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RIB vs FIB differences?

Can someone explain the differences between a RIB and FIB a little further? I didn't see any similar questions on the site so I thought this would be a good addition. The RIB routes and the FIB ...
2
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1answer
109 views

Why does Neighbor Discovery Protocol have to monitor upper-layer protocols?

While reading the RFC of NDP I wondered, why it is necessary to monitor upper layer traffic in order to know if a neighbor is reachable, e.g. a TCP ACK. I do get the IPv6 packet anyway, so I know it'...
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2answers
221 views

Cisco 800 series guide

Recently, my company bought a Cisco 881. Although I am able to get it up and working by copying some configuration on the Internet, I still do not understand how does the layer 2 (LAN) and layer 3 (...
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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 ...