The Stack Overflow podcast is back! Listen to an interview with our new CEO.

Questions tagged [layer3]

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

Filter by
Sorted by
Tagged with
10
votes
1answer
11k 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
votes
1answer
100 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'...
1
vote
2answers
196 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 (...
1
vote
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 ...
1
vote
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 ...
1
vote
2answers
509 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
votes
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
vote
1answer
49 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 ...
1
vote
2answers
1k 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
votes
2answers
9k 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
votes
2answers
255 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
votes
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
vote
1answer
342 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 ...
1
vote
1answer
72 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?
1
vote
2answers
513 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 ...
1
vote
4answers
2k 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
vote
1answer
202 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
vote
1answer
426 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 ...
1
vote
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 ...
1
vote
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 ...
1
vote
1answer
11k 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
votes
1answer
118 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 ...
4
votes
2answers
562 views

Can I Use BGP as an IGP - Multisite w Redundant Layer 3 MPLS WANs

The requirements are Hundreds of sites. Each has a router and firewall and a switch stack. Layer 3 MPLS WAN with BGP to provider VRF. BGP as an IGP? iBGP Would you distribute a public ASN across ...
1
vote
2answers
4k views

How to connect different networks based on vlans using layer 3 switches and router?

This is a simplified version of my network diagram. How do I make both network speak to each other? I'm confused because earlier I used routers and switches, and I connected them using OSPF or EIGRP....
0
votes
1answer
82 views

Use of BGP by Enterprise / Medium Businesses with Layer 3 MPLS WAN

Scenario: Assume no Internet connection for the sake of this question, the scenario is basic - 5 offices connected by an MPLS WAN. The customer is handed a Fast Ethernet (100Mbps) circuit at each ...
1
vote
1answer
621 views

Best method for rate limiting ingress & egress traffic hosts in colocation

What is the best method for the limiting speed of internet access for hosts in our colocation. We have a full rack which will be connected to the internet at 200/200 Mbps. We have our colo equipment ...
1
vote
2answers
197 views

HP 5400Rzl2 strange ACL behaviour

Hello to all of you experts. I'm sorry if this is a dumb question (I usually don't ask those, but I'm human), but I haven't a clue of what's wrong in this environment. I wish to permit all my VLANs ...
1
vote
2answers
2k views

Switching vs Routing

I have seen quite a few discussions regarding MPLS stating things like: MPLS combines the performance and capabilities of Layer 2 (data link layer) switching with the proven scalability of Layer 3 (...
1
vote
1answer
2k views

Can't ping through L3 switch

I've built a scenario in Packet Tracer that I am looking at implementing but having issues with pinging from a PC through a L3 switch. From the switch, I can ping every IP address in the environment ...
0
votes
1answer
148 views

How do protocol stacks determine the destination mac of reply packets?

Suppose a network stack receives an incoming message: Ethernet sees that EtherType is IPv4 so the payload is forwarded to the IPv4 handler IPv4 sees that the IP protocol number is ICMP so the message ...
2
votes
5answers
14k views

Difference between routing, forwarding, switching

I feel like the three terms are often used as synonyms but actually all mean something different. I did look at Wikipedia sites and at a related question but I'm still unsure about the definitions of ...
3
votes
1answer
1k views

Cisco VRFs and L2 inter-switch communication

I am having trouble wrapping my brain around a VRF concept and why two switches are communicating with each other on a particular VLAN when I don't think they should. switch1 & switch2 are ...
6
votes
4answers
3k views

In the TCP/IP model, how does the application layer inform the Internet layer of the destination IP address?

New to networking. How does the application layer inform the Internet layer of the destination IP address? Let's say I make a Http request to www.google.com, which the application layer resolves to 8....
1
vote
1answer
696 views

Ping over Trunk Port Juniper

Let's say I have one vlan on one switch and another vlan on another switch (2 EX2200 Juniper). I have a trunk between the two switches on which both vlans are members. What do I need to do to allow ...
1
vote
1answer
444 views

Calculation accounting for Layer 2 overhead when viewing traffic statistics

Recently, I was on a Juniper device, trying to figure out why I was getting a lower bit rate even though I knew I was sending a lot more. Then it hit me that Juniper devices show the Layer 3 ...
0
votes
2answers
16k views

How do you ping between VLANs?

I have created VLANs on the layer 3 switch and I would like to ping between them, how do i do so? I would like to allow VLAN 2 to ping VLAN 3, how? What command should I use? new#sh ip interf ...
1
vote
1answer
370 views

Multicast forwarding through VLANs for KVM Over Ip [closed]

I'm currently designing a terminal-server architecture, using KVM-Over-IP technology (I'm using Gefen devices) where I have four VLANs: One VLAN for the displays at 192.168.240.0/24 Three VLANs for ...
5
votes
2answers
4k views

How does a layer-2 switch work with UDP?

If UDP and/or TCP send packets via IP to an Internet Protocol Address, how can a layer-2 switch forward these? Is this possible or do you need a layer-3 switch?
2
votes
1answer
270 views

Problem with Routing in VLAN

I am trying to set up several VLAN's on a Cisco 3560 switch. These new segments should be able to communicate with VLAN 1 and even access the Internet. Basic IP information: Gateway: 10.1.1.2 VLAN1: ...
2
votes
2answers
603 views

On a Layer 3 switch, what part does the CPU play in forwarding packets?

I am a Systems Administrator at a small firm. We are latency sensitive. When forwarding packets, what protocols use the CPU and which use the ASICs? We have mostly Arista 7124's (for the most latency ...
2
votes
1answer
1k views

Load balancing between multiple layer 3 switches

I have two trunked L3 switches forming a network backbone. One is an old HP2848 and the other is a new Juniper EX3300. Currently only the EX3300 connects to our WAN Router and is trunked via 4 LACP ...
1
vote
3answers
863 views

Routing between two networks

I had a question here. Basically, we have two different networks. Each network has one Cisco 2960 layer 2 switch for each network in the same location. These are two individual networks. There is a ...
2
votes
1answer
105 views

How can fat tree ensure bandwidth?

I'm reading about fat tree and data center topologies, but I have doubts. To lower cost, "normal" tree is used sharing bandwidth to many hosts. 1:1 is not common, so we see something between 2.5:1 ...
2
votes
2answers
682 views

Exiting to a Router from Layer 3 Switch with SVI enabled routing

I am trying to simulate a network, I am having problem directing traffic to exit the L3 Switch and to go to router for routing to outside network. (I don't want to use routing capability of switch, ...
1
vote
1answer
821 views

How to use a layer 3 switch for QOS between gateway and hosts?

In the following scenario, is it possible to prioritize VOIP/RTP from x.x.x.51 through the gateway with a Cisco switch, and how? I need to prevent x.x.x.50 from saturating the WAN connection. ...
1
vote
1answer
74 views

General network comprehension

I wrote a program that does packet communication with a server and something has been in the back of my head for sometimes : When I analyze packets with WS I can see in the header first off two MAC ...
1
vote
3answers
2k views

Assign IP address to a FastEthernet port on CPT switch

I've configured a vlan 3 with ip address and then assigned FE port to vlan 3 , i read that this will assign the ip address to the FE interface. I know this is really simple configuration .But really ...
0
votes
1answer
618 views

theory: connecting two computers with ethernet cable [closed]

I am fairly new to networking but have done manual Linux command line wireless connections and home router configuration. The internet is full of how-to guides on transferring files between two ...
1
vote
2answers
289 views

How does a TCP segment go through the Internet Layer in TCP/IP?

I'm currently learning the reference models. It's said that TCP/IP supports only connectionless communication in the Internet Layer but both connectionless and connection-oriented in the Transport ...
1
vote
0answers
356 views

Optimizing access control lists on a Cisco SG500X-48 Small Business switch

I am trying to optimize the access control list rules on a Cisco SG500X-48 Small Business switch (on Layer 3). The general aim is to regulate the traffic between two VLANs (e.g., 10 and 30) in such a ...