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14
votes
3answers
62k views

Is the “default VLAN” simply the default native (untagged) VLAN on all interfaces that have no configuration?

... or does the "default VLAN" have some wider meaning? Also, can it / should it be changed? For instance, if a switch is going into part of a network that is only one VLAN and it's not VLAN 1, is ...
13
votes
1answer
13k views

What is the 5 level QoS model (through config example)?

I have heard people stating that their network "operates a 5 level (or layer) QoS model" Sometimes they also mention a 7 level QoS model. Can anyone provide me with a Cisco IOS config example of ...
22
votes
8answers
9k views

Why can't devices on different VLANs, but on the same subnet, communicate?

I have a question about switching. I have two devices connected to a switch with IP addresses 192.168.5.20 and 192.168.5.10. Both devices have the same prefix, /24. That means they are on the same ...
19
votes
5answers
88k views

Cable Colors and Purpose

I've been doing some work with some big businesses and so far I've learned yellow is internet and blue is phone. Is this a standard or is this just a personal chose? Do colors mean different tasks?
18
votes
5answers
83k views

About the switchport mode

I am new to network Engineering. I find it is hard to distinguish and understand different switchport settings. Why can I have a switchport set to access, auto, or dynamic? What are they used for? ...
16
votes
7answers
101k views

What are the differences between VRRP and HSRP?

Are there any significant differences between VRRP and HSRP?
10
votes
3answers
10k views

Why don't switches rewrite mac-addresses?

Is there any particular reason why Ethernet switches don't change the MAC address of a packet? Is it for end host identification using the MAC address, or anything else?
9
votes
3answers
10k views

Is a TCP three-way handshake required for an HTTP POST?

I don't quite understand if i posting http form data from the browser to the server, does the protocol still need to make three-way handshake (syn-ack-data) or it only works for GET http requests?
21
votes
7answers
33k views

Difference between access list and prefix list?

Can someone explain with an example whats the difference between an access list and prefix list.
19
votes
4answers
5k views

Jumbo Ethernet Frame Deployment

What are some general guidelines for the successful deployment of jumbo frames in a routed environment?
17
votes
2answers
56k views

How does a WiFi range extender work?

I have a WiFi base station, and a WiFi range extender. Both of them have the same SSID. When a device connects to that SSID, what exactly happens? How does the device know that base station and range ...
16
votes
12answers
35k views

What would cause high latency anytime there is traffic on WAN?

I have a network that has been experiencing slow internet speeds. After a great deal of troubleshooting, I have determined that any streaming content/downloads will cause the latency of WAN traffic to ...
13
votes
5answers
14k views

Why does OSPF need Type2 LSAs?

Learning more about OSPF for CCNP studies. I'm looking at how OSPF builds its links, and have just covered Type1 LSAs. Looking at Type1 LSAs, I'm wondering why these are even necessary? The book ...
12
votes
2answers
13k views

Technical difference between a Collision and Broadcast Domain

Many people new to networking wonder what the technical differences between a broadcast domain and a collision domain are. Specifically: What criteria is used to know the boundaries of a collision ...
12
votes
7answers
3k views

Accurate strategy for measuring point-to-point link performance?

I have a requirement to provide an accurate means to demonstrate line performance over a flat layer2 1Gb point-to-point Ethernet circuit, approx 100 miles apart that seemingly goes through a number of ...
11
votes
3answers
6k views

What are the alternatives to OTV for stretching a layer 2 network across 2 datacenters?

We want to find a "safe" way to stretch layer 2 network across 2 data-centers, and since we don't have any equipment running NX-OS on either data-centers we can't use OTV. So what are the alternatives ...
9
votes
3answers
6k views

Generate list of subnets on switch using SNMP?

Is anyone familiar with an approach to generate a list of subnets on a particular switch (let's pick a more popular one - Cisco) using SNMP? How about a list of VLANs? If so, can you point me to the ...
9
votes
1answer
71k views

What does TCP DUP ACK mean?

In Wireshark, I see TCP duplicate ACK packets sent from the receiver to the sender. What does it mean? Does it imply packet loss? Thank you
9
votes
3answers
15k views

Whats's the function of a loopback interface in routing protocols?

So I've got this task where I have to setup a virtual network with an OSPF routing protocol. I firstly ignored this loopback interface I had to configure on the routers since it didn't do any ...
9
votes
3answers
1k views

VM on a client connected to a Cisco 1262 unable to DHCP (but IPv6 works fine)

I recently replaced wireless at a site from the internal AP on an 877-WM with a (standalone) 1262 running 15.2(2)JB. I've configured the AP pretty much the same as I always do for Cisco AP's for ...
29
votes
3answers
7k views

What is “oversubscription” in Networking?

I have a question about oversubscription in networking. I read a lot of documentation but I still don't understand what it means. I read the following on the Cisco website, oversubscription of the ...
25
votes
7answers
10k views

Why does DHCP use UDP and not TCP?

DHCP uses UDP as its transport protocol. DHCP messages that a client sends to a server are sent to well-known port 67 (UDP—Bootstrap Protocol and DHCP). DHCP Messages  that a server sends to a client ...
19
votes
5answers
18k views

Should portfast be used on a port potentially connecting to an unmanaged switch?

I understand the basics of how spanning tree works and why you would want to use portfast on user access ports. When dealing with a topology with a large number of dumb switches under desks and ...
16
votes
3answers
63k views

How is the root bridge elected in STP?

How does STP/RSTP determine which bridge is the root bridge, and how are paths to the root bridge selected?
15
votes
5answers
93k views

What's the difference between an Ethernet cable and a UTP cable?

Is there such a thing as an Ethernet cable or technically no? Are they actually called UTP cables? From wikipedia UTP cables are found in many Ethernet networks and telephone systems.
13
votes
5answers
4k views

How exactly does an Ethernet collision happen in the cable, since nodes use different circuits for Tx and Rx?

I am trying to understand how a collision occurs in Ethernet, especially when a duplex mismatch exists or when on a legacy Ethernet network two nodes transmit simultaneously. Everyone explains the ...
12
votes
1answer
6k views

Translating SNMPWALK output into human-readable format

I am asking this question which is related to a question I previously asked and was comprehensively answered by @MikePennington. When I asked that question, I intended to know how to poll arp table ...
10
votes
3answers
21k views

VRFs, VLANs and subnets: difference

I have a basic understanding of VRFs, VLANs and subnets. I understand that VLANs operate on L2, and subnets and VRFs (lite) on L3. What I don't understand, is why you would choose one over the other ...
10
votes
4answers
18k views

Two hosts of different subnets connected to switch

Two host of different subnets, let it be A - 10.1.2.1/24 and B - 10.1.3.1/24 be connect to the same switch S. Can they communicate? So as far I understand: A sends a packets with IP of B S receives ...
10
votes
4answers
29k views

converting AP from CAPWAP to autonomous - BVI1 interface gets reverted back to DHCP

Has anyone ever gotten this message in the middle of converting a CAPWAP access point from CAPWAP to autonomous? *Mar 1 00:47:59.399: %CAPWAP-3-STATIC_TO_DHCP_IP: Could not discover WLC using static ...
9
votes
1answer
13k views

What are EUI-48 and EUI-64?

What are EUI-48 and EUI-64 addresses formed and used? Give me examples. What are MA-L, MA-S and MA-M assignments? I have read https://standards.ieee.org/develop/regauth/tut/eui48.pdf and https://...
6
votes
2answers
6k views

Why Don’t Probe Requests for Specific SSIDs include BSSIDs

I'm looking at WLAN traffic captured from wireshark on monitor mode and notice that out of the 67,000 probe requests, 99.08% have the destination set to FF:FF:FF:FF:FF:FF (Broadcast). The thing is, ...
4
votes
3answers
57k views

How to know at what OSI Layer(s) does a firewall operate

I understand that Firewalls may operate on different OSI layers depends on the firewall itself. but how can I know if I install specific firewall at what OSI Layer(s) it does operate ?
26
votes
2answers
126k views

TCPDump - Filter by MAC Address

I would like to display all traffic for or from a specific MAC address. For that I tried sudo tcpdump host aa:bb:cc:11:22:33 It does not work and returns me an error tcpdump: pktap_filter_packet: ...
23
votes
4answers
9k views

Can I use a Catalyst 2960-S for iSCSI?

I need to set up a modest iSCSI SAN with a few ESX hosts and one storage array. Can I get by using a Catalyst 2960-S or do I need to upgrade? Are there any special tweaks I need to make to the switch ...
19
votes
3answers
7k views

What factors drive a Cisco IOS upgrade?

In order of preference/priority, what factors do you consider in driving an upgrade (or downgrade) with Cisco IOS? If no compelling factors exist, how long would you allow a particular version of IOS ...
19
votes
3answers
5k views

Why is broadcast used at the DHCPREQUEST step?

This is the process of DHCP operation, My question is at the 3rd step why does the Client send a Broadcast and not a Unicast as after the previous two operations the address of the DHCP server / ...
13
votes
4answers
1k views

Possible (bit) patterns of a netmask

Given a prefix Y, it's easy to calculate the corresponding netmask: Put Y times a set bit, and then fill up "to the right" with zeros until one has 32 bits (IPv4) in total. Example: Prefix 24, thus ...
13
votes
3answers
5k views

Management network. Best practises: big VLAN or routed interfaces

We are going to deploy a campus network with approximately 50 switches (Core, Agg, Access). Some of them will be L2 (20), and others will be L3 (30). We are thinking about how to manage these devices: ...
11
votes
2answers
1k views

Who pays for traffic when it transits multiple providers

TLDR Question: Who pays for traffic when it transits multiple providers Original Question I know there are a great many sites out there with this question and answer, but as yet I have not been ...
11
votes
2answers
14k views

Directed and Limited Broadcast confusion

Let's say I am on a network 192.168.1.X and I use the below ping commands. ping 255.255.255.255 ping 192.168.1.255 Why we are calling 1st one as limited and 2nd one as directed ? In what category ...
11
votes
2answers
17k views

Preventing STP loops in etherchannels configurations

What is the best practice when configuring etherchannel on Cisco switches to prevent a STP loop/broadcast storm when etherchannel is mis-configured? I had an instance where 2 ports on a switch were ...
10
votes
4answers
4k views

how to get scp via snmp to work with cisco routers?

I have a lab setup where I'm trying to use SCP via SNMP to a cisco router.I found some online documentation such as: http://ccie20728.wordpress.com/2008/05/20/get-the-cisco-configuration-over-snmp/ ...
10
votes
4answers
15k views

speed/duplex mismatch

How do mismatches occur; what is the impact of a mismatch on network connectivity; is resolution of mismatches really worth the effort; what are some ways to detect mismatches on a large scale?
8
votes
2answers
23k views

Window Size and ACK Number

Copy-pasting from my lecturer's slides: • Receiver indicates the window size is 3000 • Transfer goes ahead • Acknowledge every 3000 bytes • Receiver increases window size to 4000 • 4000 bytes ...
7
votes
4answers
4k views

Why is a TCP Socket identified by a 4 tuple?

Newbie to networking here. I'm reading the Computer Networking (3rd edition) book, and in section 3.2 they are discussing multiplexing / demultiplexing for both UDP and TCP. In the UDP protocol, a ...
7
votes
3answers
25k views

ARP request outside of LAN; Target machine or router response?

If I sent an ARP request to the target machine, which is in over Internet and has 2 routers between, what will the target IP address on my request (0001) packet be? Will it be the Router IP address, ...
7
votes
2answers
22k views

Can I truly multicast over WIFI?

Am streaming UDP over wifi (5ghz) - approx 1.5k/packet... trying to stream to ~10 devices simultaneously, with extremely low latency.. As I understand Wifi, it can never true multicast, as each ...
6
votes
1answer
10k views

How do you configure a TACACS+ tac_plus server on Ubuntu 16.04 that authenticates against Microsoft Active Directory?

How do you configure a TACACS+ tac_plus server on Ubuntu 16.04 that authenticates against Microsoft Active Directory?
6
votes
2answers
740 views

is there a difference between Latency and speed ?

so latency is the time it takes for bits to get from the sender to the receiver and the speed is how fast bits travel , so logically the more speed the network has the more low latency it has ...

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