A router must maintain a separate routing table for each active routing protocol, because each active routing protocol uses a different addressing scheme (such as IP6, IPv6, and PIX).
Protocols that send routing update packets are called active routing protocols (such as RIPv1, RIPv2, EIGRP, and OSPF).
By default, the router will not forward any broadcast or multicast packets.
If desired, routers can provide Layer 2 bridging, while simultaneously transmitting over the same interface.
Routers can provide Quality of Service (QoS) for certain types of network traffic
The data link layer provides the physical transmission of data. Use hardware addressing.
During the routing process, the packet itself is never changed, it is just encapsulated with the control information it needs for proper transmission to different media types.
The only way to stop broadcast storms from spreading in the internet is to use layer 3 devices – routers.
Half-duplex Ethernet (using a pair of cables) – typically is 10BaseT – is only 30% to 40% efficient.
Full-duplex Ethernet （using two pairs of cables) – In theory, 10Mbs Ethernet in full-duplex mode results in a transmission rate of 20Mbs. 200% efficiency.
All devices except hubs can run full duplex.
There are no collision domains in full duplex mode.
The host’s NIC and switch ports must be able to operate in full-duplex mode.
Three types of cables
The V.35 interface is used for serial connection to the WAN.
To communicate and exchange information, each layer uses Protocol Data Units (PDUs), which are usually appended to the header of the data field, but can also be appended to the trailer of the data field.
From high to low PDU representation segment–packet–frame–bit
The transport layer uses port numbers to define virtual circuits and upper-layer processes.
The transport layer receives the data stream, assembles it into segments, and establishes a reliable session by creating virtual circuits. It then sorts (numbers) each segment and uses acknowledgment techniques and flow control (SYN, Windowing, etc.).
Cisco’s three-tier model
Core layer (Core)–backbone
Distribution layer (Distribution)–routing
Access layer (Access)–exchange
High reliability Consider adopting data link layer technologies that are beneficial to both speed and redundancy, such as FDDI, FastEthernet (with redundant links), and set up ATM. YESLAB.net Cisco Technologies
Low Latency Choose a routing protocol with a short convergence time. Fast and redundant data link connections are meaningless if routing tables are slow to converge.
The distribution layer is where the network policy is implemented.
Design of the distribution layer
Implementation of the tool Such as access tables, packet filtering and sorting.
Implementation of network security and network policy Including address translation and firewall.
Redistribute routing protocols. Including static routes.
Routing between VLANs and other functions supported by working groups.
Define broadcast domains and multicast domains.
The rapid development of the Internet has made the Cisco Certified Professional Engineer CCNA a primary certification, and also has advanced certifications such as CCNP, CCDP, CCNP Specialization, CCDP Specialization and the highest level of CCIE certification. The whole set of certification mainly focuses on network maintenance and network design.