Modern network interfaces include options for either electrical or optical media types. In this section, you will learn about fiber-optic networks. Fiber-optic media has many advantages over copper in most deployments. For example, fiber cables are not subject to electrical magnetic interference since they transmit optical, not electrical, signals. Fiber cables are much more difficult to tap into than copper and offer a higher level of security. Fiber optics support much higher transmission speeds than copper, with new breakthroughs of transmitting data over optical cable in the terabits per second range. With the use of laser technologies and the optical characteristics of single-mode fiber, the distances between repeaters are much greater than that of copper transmission technologies.
A vendor may ship hardware with open slots called small form-factor pluggable (SFP) options. The SFP port is a slot on a switch, router, or computer into which SFP transceivers are inserted. This allows us to purchase the SFP module that meets our requirements and slide it into the open SFP slot, as shown in Figure 6.2. SFPs are also called mini-GBICs and must match the cable type and wavelength at both ends.
FIGURE 6.2 Small form-factor pluggable interfaces
The AWS Direct Connect facilities use optical interfaces for the interconnection between their network equipment and yours, or your service provider’s. AWS has three available connection speeds of either 1, 10, or 100 Gigabit Ethernet using single-mode fiber. 1 Gigabit uses the 1000BASE-LX (1310 nm) SFP transceiver, 10 Gigabit uses the 10GBASE-LR (1310 nm) SFP transceiver, and for 100 Gigabit, the 100GBASE-LR4 SFP transceiver is used. Remember that single-mode optics are the only type supported by AWS and that a single mode on one end will not establish a link to a multimode on the other end. The media type and optics must match on both ends. You must disable autonegotiation for each 10G and 100G interface. 1G interface autonegotiation configurations may vary based on location. If you have issues establishing a link, refer to the AWS online documentation about troubleshooting layer 2 issues at https://docs.aws.amazon.com/directconnect/latest/UserGuide/Troubleshooting.html#ts-layer-2.
Other requirements for the DX interconnection are that 802.1Q VLAN encapsulation must be supported on each end of the interconnected interfaces at the DX location. This includes any intermediate devices at the DX. Your router connection from the premise data center to the Direct Connect facility must support the BGP routing protocol with MD5 authentication capabilities. Bidirectional forwarding can be enabled to detect asymmetric cable failures. AWS enables BFD on their interfaces, but the feature does not activate until your interface enables BFD.
In this section, we will review layer 2 of the OSI model, which is commonly referred to as the data link layer. After the review, you will learn about the data link features that are specific for you to know for the exam including VLANs, link aggregation, and jumbo frames. The unit of data at layer 2 is called the frame. The layer 2 data link format is the frame, and the layer 3 data is called a packet. Layer 2, or data link layer, is concerned with local delivery of frames between nodes on the same local area network.
The frame flows down to the physical layer, or layer 1, and the data link relies on layer 1 to be operational and to send data to the remote end. Layer 2 networks can run over many types of layer 1 media including copper, fiber, coax, and wireless. There are several different layer 2 standards and protocols in use, with Ethernet being the most prevalent so it will be the focus of this section.
Layer 2 frames are addressed using a burned-in unique hardware address for each device. When using an Ethernet frame, this access is called a Media Access Control (MAC) address. Each MAC address is 48 bits long, is expressed in hexadecimal format, with the first 24 bits identifying the hardware vendor called the Organizationally Unique Identifier (OUI), and the last 24 are used to identify each device, or endpoint, as shown in Figures 6.3 and 6.4. The Ethernet hardware address on every interface in the world is required to be globally unique; there are no two devices with the same MAC address in the world.
If the MAC address is sent out on the network as all ones (all Fs in hexadecimal), then it is a broadcast sent to all listeners on that segment.
FIGURE 6.3 Ethernet MAC address
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