Questions tagged [layer3]

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

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1answer
7k 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.
2
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1answer
57 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
1k 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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2answers
6k 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-...
2
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1answer
248 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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1answer
146 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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1answer
604 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
211 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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2answers
1k 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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3answers
2k 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. ...
2
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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
486 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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2answers
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
1k views

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 ...
4
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3answers
5k 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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2answers
5k 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 ...
4
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3answers
985 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
672 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?
2
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2answers
79 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. ...
4
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1answer
950 views

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 ...
3
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4answers
165 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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1answer
38 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
804 views

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
1k 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 ...
2
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2answers
352 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 ...
2
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3answers
196 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 ...
11
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1answer
17k views

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
104 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
204 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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1answer
2k 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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2answers
3k 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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2answers
567 views

mLACP or vPC on L3 interfaces

I just want to know if it's possible to implement mLACP (with VSS) or vPC on L3 interfaces. I just can't find any answer to this on cisco doc. Thanks,
12
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1answer
2k views

Can a router send ARP requests to hosts?

I play with libpcap in C recently to create an arp sniffer program that captures arp requests on the air. I came up with a strange effect. I captured arp requests from my router. I don't know if this ...
1
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1answer
56 views

Need Advice From Experienced Techs Please - For Charity Organization in Africa [closed]

1st: I would like to thank you for your time. 2nd: I was asked by a charity organization to help building a system and network for the charity center where they help the most needed groups in the ...
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2answers
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....
3
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2answers
11k views

Mac address and IP address in physical addressing in Data-Link layer

Framing is done in Data-Link layer. We give physical addresses there. Destination address, source address and MAC. If two PCs in different networks, we try to sent data from one another, we specify ...
2
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2answers
376 views

Lowest Possible Failover Latency

Let’s say I have two networking devices (either L2 switches, L3 switches, or routers), and the two devices have two ethernet connections between them: port 1 to port 1, and port 2 to port 2. If one of ...
3
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2answers
2k views

Encapsulation and decapsulation basics for OSI layer

I have read that encapsulation takes place down the layers while decapsulation takes place up the layers. In essence, the encapsulation starts at Application layer all the way upto Physical layer. ...
1
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1answer
390 views

Regarding Bridge domain and L2 vpn

I am trying to understand the usage of bridge group command.Please refer the following config(on switch ASR9k): l2vpn ! bridge group TEST1 bridge-domain BD1 interface Bundle-Ether1.500 ...
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1answer
87 views

How does a network cryptor work?

I want to know at which layer is a network cryptor used. What are the features of routers used for encrypted packets?
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2answers
641 views

Understanding Broadcast address

Please validate my understanding for the following points with regard to broadcast address: 1.Broadcast address is relative to a network, so every n/w will have it's own broadcast adress(I can obtain ...
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4answers
3k views

Configuring 2 layer 3 switch with VLAN

I am trying to create 2 vlans- 10 and 20 where 10 is for user and 20 is for DMZ. vlan 30 created is to link between vlans 10 and 20. Right now I'm only able to ping user from vlan to their switch and ...
1
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1answer
260 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 ...
1
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1answer
824 views

Help setting up multiple IP ranges on same subnet

So long story short. We setup our network YEARS ago, when we were a small company of only 10 people. Now, we are pushing 100 employees, and my network has outgrown itself. Originally, I setup the IP ...
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2answers
2k views

Is there a way to detect whether router is ASBR in OSPF?

Am using open source OSPF software from ospf.org and running ospf daemon in host PC. If router has interfaces in multiple area, then its an Area Border Router. Is there a way to detect the router is ...
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3answers
1k views

HSRP Issue Both sides are active ( Layer 3 4300 X serires)

Why does HSRP shows both sides are active HSRP? Could you please give me details answer? First router: **Vlan111 - Group 6** State is Active 5 state changes, last state change 2w4d Virtual ...
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1answer
13k views

How can I apply an ACL to interface on a Layer 3 switch?

I try to accept ACL on L3 switch inteface. I've created standard ACL via: SW-L3(config)#access-list 1 permit host 1.1.1.2 SW-L3(config)#access-list 1 permit host 1.1.1.3 Then i tried to execute this,...
2
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1answer
139 views

If a bypass switch is an L1 device, what happens when bypass mode is enabled?

Okay, a bypass switch works at L1, and when an inline appliance like an IPS or firewall is connected to the bypass switch, the bypass switch simply grabs all traffic coming in an either side and ...