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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
7answers
99k views

What are the differences between VRRP and HSRP?

Are there any significant differences between VRRP and HSRP?
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
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
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 ...
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
5k 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
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 ...
8
votes
3answers
9k 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?
19
votes
5answers
17k 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
62k 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?
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 ...
15
votes
5answers
92k 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
5k 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
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 ...
10
votes
3answers
19k 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 ...
9
votes
3answers
14k 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
1answer
12k 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://...
9
votes
6answers
3k views

Do network adapters read incoming bits in a single stream?

When a Gigabit network adapter is receiving data, how is it receiving the bits? Is it seeing it all in one stream of 0's and 1's? Or is there somehow multiple streams of 0's and 1's coming in at the ...
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
56k 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 ?
25
votes
1answer
123k 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
4k 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 / ...
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 ...
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
16k 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
17k 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
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
22k 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
1answer
66k 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
7
votes
2answers
21k 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
2answers
699 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 ...
6
votes
1answer
9k 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?
4
votes
3answers
9k views

Inter-switch IGMP on a VLAN with two switches, and a multicast source per switch

I have a network consisting of two HP 2810 switched. Attached to each switch is, on one port, a multicast video coder, and on a different port, a decoder. There are two VLANs - a control VLAN (...
3
votes
1answer
2k views

What is the need for transport Layer?

In 5-layer model. Why we need additional transport layer? I read these two points Users who interact with software have no control over the sub-net; Transport Service can provide a more reliable ...
35
votes
3answers
2k views

Why do network taps have four ports?

I've been looking at a hardware network tap like this one to replace a pseudo-permanent SPAN that's been running on a Catalyst switch. All the taps I find have four interfaces: A, B, and two output ...
22
votes
8answers
50k views

How can I force VTP clients to update their VLAN database from the VTP server, on Cisco devices?

I was doing some cisco exercises on configuring a vtp server and client, something I can't figure out is : I setup a vtp server, added my VLAN's I then took another switch that was attached to this ...
19
votes
1answer
4k views

What is the practical use of a /31 CIDR or 255.255.255.254?

With a /31 subnet, we are left with zero usable hosts. The /31 subnet only has two hosts - one for network and another for broadcast. I am wondering why would someone ever use this subnet.
18
votes
4answers
7k views

Can DHCP Server determine client's OS? [closed]

Is it possible for the DHCP Server to determine the client operating system? I'm working on a monitoring tool for gateways on local networks that is web-based and would like to be able to somehow ...
15
votes
6answers
9k views

Reason for half-duplex mode in Ethernet?

Half-duplex connections were popular at the time of 10Mbps and 100Mbps Ethernet, and, according to standards, it is allowed also in case of 1Gbps Ethernet. Am I correct that half-duplex mode support ...
15
votes
2answers
3k views

Serialization and serialization times in 40G/10G and 100G/25G Ethernet

I've recently been involved in discussions about lowest-latency requirements for a Leaf/Spine (or CLOS) network to host an OpenStack platform. System architects are striving for the lowest possible ...
14
votes
5answers
2k views

How to filter non-bogon prefixes received via BGP from an Internet Exchange(IXP)?

When connected to an Internet peering exchange(IXP), what is a good way to make sure that people don't send you prefixes that they shouldn't be announcing? With regards to bogons I'm aware of the ...
14
votes
3answers
41k views

How to Monitor Vlan Traffic?

We have migrated to a new ISP who provide us several services (Internet+VoIP+VoD) and have divided each service in one vlan 100,101,102 respectively. Now I'm looking for a solution to monitor each ...
13
votes
4answers
16k views

MTU and Fragmentation

Consider the following: NAS with 10G interface connected to 10G interface on switch. Client computers connected to switch via gigabit Ethernet. Will there be any gain in performance if MTU size is ...

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