从广义上来看,网络交换机分为两种:广域网交换机和局域网交换机。广域网交换机主要应用于电信领域,提供通信用的基础平台。而局域网交换机则应用于局域网络,用于连接终端设备,如PC机及网络打印机等。从传输介质和传输速度上可分为以太网交换机、快速以太网交换机、千兆以太网交换机、FDDI交换机、ATM交换机和令牌环交换机等。从规模应用上又可分为企业级交换机、部门级交换机和工作组交换机等。各厂商划分的尺度并不是完全一致的,一般来讲,企业级交换机都是机架式,部门级交换机可以是机架式(插槽数较少),也可以是固定配置式,而工作组级交换机为固定配置式(功能较为简单)。另一方面,从应用的规模来看,作为骨干交换机时,支持500个信息点以上大型企业应用的交换机为企业级交换机,支持300个信息点以下中型企业的交换机为部门级交换机,而支持100个信息点以内的交换机为工作组级交换机。 [3] 

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In August 2019, Coinbase announced that it was targeted by a sophisticated hacking attack attempt in mid-June. This reported attack used spear-phishing and social engineering tactics (including sending fake e-mails from compromised email accounts and created a landing page at the University of Cambridge) and two Firefox browser zero-day vulnerabilities. One of the Firefox vulnerabilities could allow an attacker to escalate privileges from JavaScript on a browser page (CVE-2019–11707) and the second one could allow the attacker to escape the browser sandbox and execute code on the host computer (CVE-2019–11708). Coinbase's security team detected and blocked the attack, the network was not compromised, and no cryptocurrency was stolen.[39][40][41]

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For those of you who have not been paying attention to one of the biggest trends in investing and tech, cryptocurrencies are digital currencies using encryption techniques that regulate the generation of currency and verify the transfer of funds, operating independently of a central bank. Units of currency are created through a process referred to as mining.

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I have not been using Coinbase long but I have used it long enough to feel like I’m getting burned. I am using Coinbase as, what I call, a pass through as in the end, I am purchasing crypto that is not supported by Coinbase with the BTC I purchase through Coinbase. While the app itself is great as it is easy to navigate the process of withdrawing funds is not so great. I purchased BTC with the intent of withdrawing to purchase another crypto. A week and several emails later my BTC has not yet been released for withdraw. Prior to this transaction I had done several others successfully with no issues, now, for no reason whatsoever my funds are pended for “further research”. I am a patient person but as I’m sitting here waiting the BTC value is falling and the cost of the crypto I am looking to purchase is rising which means at this point I have missed out on a few hundred dollars of profit all because Coinbase won’t release my funds. I am giving only 1 star because (1) communication with Customer Service has not been great as I am still sitting here clueless on what’s going on and (2) I’ve missed out on significant profit and have no idea why or have any sense of comfort that this won’t be an ongoing issue

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The other 2% of customer funds, held online, are covered in the event of a breach of Coinbase's online storage. Also, Coinbase holds all customer fiat currency in custodial bank accounts, on behalf of customers. So, if you have fiat currency in Coinbase, in a USD wallet, it is covered by FDIC insurance up to $250,000 (just like a "regular" bank). This protects customer assets (so long as they have been converted to fiat currency) even in the event of Coinbase becoming insolvent.

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In February 2019, Coinbase announced that it had acquired "blockchain intelligence platform" Neutrino, an Italy-based startup, for an undisclosed price.[33] The acquisition raised concern among some Coinbase users[34] based on Neutrino founders' connection to the Hacking Team, which has been accused of providing internet surveillance technology to governments with poor human rights records.[35] On March 4, 2019, Coinbase CEO Brian Armstrong said his company "did not properly evaluate" the deal from a due diligence perspective and thus any Neutrino staff who previously worked at Hacking Team "will transition out of Coinbase."[36]

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In the case of Bitcoin, miners run computer programs to verify the data that creates a complete transaction history of all Bitcoin. A technology known as the blockchain, which is used to create irreversible and traceable transactions, makes the process of verification possible. Once a miner has verified the data (which comes in a block, hence, blockchain), they are rewarded with some amount of digital currency, the same currency for which they were verifying the transaction history. So mining Bitcoin, for example, would earn you Bitcoin.
         其原理是:假设两个使用IP协议的站点A、B通过第三层交换机进行通信,发送站点A在开始发送时,把自己的IP地址与B站的IP地址比较,判断B站是否与自己在同一子网内。若目的站B与发送站A在同一子网内,则进行二层的转发。若两个站点不在同一子网内,如发送站A要与目的站B通信,发送站A要向“缺省网关”发出ARP(地址解析)封包,而“缺省网关”的IP地址其实是三层交换机的三层交换模块。当发送站A对“缺省网关”的IP地址广播出一个ARP请求时,如果三层交换模块在以前的通信过程中已经知道B站的MAC地址,则向发送站A回复B的MAC地址。否则三层交换模块根据路由信息向B站广播一个ARP请求,B站得到此ARP请求后向三层交换模块回复其MAC地址,三层交换模块保存此地址并回复给发送站A,同时将B站的MAC地址发送到二层交换引擎的MAC地址表中。从这以后,当A向B发送的数据包便全部交给二层交换处理,信息得以高速交换。由于仅仅在路由过程中才需要三层处理,绝大部分数据都通过二层交换转发,因此三层交换机的速度很快,接近二层交换机的速度,同时比相同路由器的价格低很多。

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Coinbase has two core products: a Global Digital Asset Exchange (GDAX) for trading a variety of digital assets on its professional asset trading platform, and a user-facing retail broker of Bitcoin, Bitcoin Cash, Ether, Ethereum Classic, and Litecoin for fiat currency.[24] It also offers an API for developers and merchants to build applications and accept payments in both digital currencies. As of 2018, the company offered buy/sell trading functionality in 32 countries,[42] while the cryptocurrency wallet was available in 190 countries worldwide.[43] On March 26, 2018, Coinbase announced their intention to add support for ERC-20 tokens.[44]
Coinbase is a terrible and unprofessional company. They’ve ignored my requests for escalation after providing no feed back on the issues I am having. These issues are costing this customer not only monetarily, but due to the lack of transparency with new policies in which coinbase will hold your funds hostage for 10 days while advising that it can be transferred “instantly” is not only false, but malicious contempt.

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Coinbase was founded in June 2012 by Brian Armstrong and Fred Ehrsam.[6][7] Blockchain.info co-founder Ben Reeves was part of the original founding team but later parted ways with Armstrong due to a difference in how the Coinbase wallet should operate.[8] The remaining founding team enrolled in the Summer 2012 Y Combinator startup incubator program. In October 2012, the company launched the services to buy and sell bitcoin through bank transfers.[9] In May 2013, the company received a US$5 million Series A investment led by Fred Wilson from the venture capital firm Union Square Ventures.[10] In December 2013, the company received a US$25 million investment, from the venture capital firms Andreessen Horowitz, Union Square Ventures (USV), and Ribbit Capital.[11]
Bitcoin (BTC) is the world’s first decentralized digital currency and payment system and is by far the most known and valuable cryptocurrency. It was created in 2009 by an anonymous person or group called Satoshi Nakamoto. Bitcoin enables transactions to be sent peer-to-peer without passing through a central authority. The transactions are recorded on a decentralized public ledger called the blockchain and each payment acquires a small transaction fee to cover the cost of the network. The total supply of Bitcoin is 21 million and it’s smallest unit of bitcoin is called a Satoshi, it’s a hundred millionth of a bitcoin – 0.00000001 BTC. The creation of Bitcoin’s is happening through mining. Miners have the task to validate transactions and keep the network secure. Their efforts are rewarded by new minted Bitcoins and transactions fees. Bitcoin can be exchanged for fiat or other cryptocurrencies, products and services. Over 100,000 merchants and vendors accepts bitcoin as a payment.

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don’t use coinbase. They held my funds and I couldn’t use my bitcoins until their value dropped by 1/4. this company is awful. I verified my ID, bank account, email, and everything and they lied and said initially it takes 3-4 days for funds to be available. once the bought the bitcoin they said it will take one week. and that is still a lie because after one week the funds are NOT available. liars !!!! 

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In 2014, the company grew to one million users, acquired the blockchain explorer service Blockr and the web bookmarking company Kippt, secured insurance covering the value of bitcoin stored on their servers, and launched the vault system for secure bitcoin storage.[12][13][14] Throughout 2014, the company also formed partnerships with Overstock, Dell, Expedia, Dish Network, and Time Inc. allowing those firms to accept bitcoin payments.[15][16][17][18] The company also added bitcoin payment processing capabilities to the traditional payment companies Stripe, Braintree, and PayPal.[19]

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Bitcoin is the world’s first cryptocurrency which works on a completely decentralized network known as the blockchain. The blockchain network consists a link of blocks that are secured using cryptography and record all the transactions. Bitcoin was first presented to the world in 2009 by an anonymous identity known as Satoshi Nakamoto. As Bitcoin works on a decentralized network, it is completely free from the involvement of third-party financial institutions or central banks. The Bitcoin blockchain facilitates instant peer-to-peer transactions at minimum transactions fees required to maintain the network. The total number of Bitcoins is fixed at 21 million with its smallest unit being referred to as Satoshi. Each Satoshi represents a hundred millionth part of Bitcoin which means that 100,000,000 Santoshi = 1 BTC. Additional Bitcoins are generated by a process known as mining. Bitcoins are mined by professional miners solving complex computational equations. For each Bitcoin mined, the miners are rewarded with either more coins or transaction fees. The miners also validate all transactions on the Bitcoin network as well as look after the network security. Bitcoin can be exchanged with fiat currencies or other digital currencies. There are over 100,000 merchants and vendors accepting Bitcoin all over the world.
On February 16, 2018, Coinbase admitted that some customers were overcharged in error for credit and debit purchases of cryptocurrencies. The problem was initiated when banks and card issuers changed the merchant category code (MCC) for cryptocurrency purchases earlier this month. This meant that cryptocurrency payments would now be processed as "cash advances", meaning that banks and credit card issuers could begin charging customers cash-advance fees for cryptocurrency purchases. Any customers who purchased cryptocurrency on their exchange between January 22 and February 11, 2018 could have been affected. At first, Visa blamed Coinbase, telling the Financial Times on February 16 that it had "not made any systems changes that would result in the duplicate transactions cardholders are reporting." However, the latest statement from Visa and Worldpay on the Coinbase blog clarifies: "This issue was not caused by Coinbase."[45]

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