As can be seen from the figure below, all the components of Enterprise Edge are connected to the Enterprise Campus Core.
As seen in the diagram below, the remote worker using PSTN connects to Remote Access VPN module of Campus Edge.
Campus Core layer connects to the Data Center/Server Farm. In a campus, server farm is centralized, and requires connectivity to the Campus Core network.
Data Center Facility Considerations:
a. Architectural and mechanical specifications
b. Environmental conditions
c. Physical security Access to the site
d. Compliance and regulation
Typical power consumption levels by different components of a Data center are as given below:
1. Lighting : 3%
2. Cooling : 50%
3. Network equipment : 10%
4. Server and storage : 26%
5. Conversion losses : 11%
Note that the cooling systems consume significantly higher power than the remaining, and depends mainly on the heat generated by the data center equipment.
The cabinets and racks should be arranged in the data center with an alternating pattern of "cold" and "hot" aisles. The fronts of the racks face each other and draw cold air into the rack to cool rack mounted IT devices (i.e. servers, switches, etc.). Conversely, the rear sides of the rows of racks face one another, expelling the hot air into the hot aisle. The issue with hot aisle/cold aisle designs is that the air is free to move wherever it will.
Spanning tree: During the process of Spanning-Tree Algorithm execution, some redundant ports need to be blocked. This is required to avoid bridging loops. To choose which port to use for forwarding frames, and which port to block, the following three components are used by the Spanning-Tree Protocol:
1. Path Cost: The port with lowest path cost is placed in the forwarding mode. Other ports are placed in blocking mode.
2. Bridge ID: If the path costs are equal, then the bridge ID is used to determine which port should forward. The port with the lowest Bridge ID is elected to forward, and all other ports are blocked.
3. Port ID: If the path cost and bridge ID are equal, the Port ID is used to elect the forwarding port. The lowest port ID is chosen to forward. This type of situation may arise when there are parallel links, used for redundancy.
During the process of Spanning-Tree Protocol execution, Root switch (say, switch A) is elected first. Next, the switch closest to the root switch is selected. This switch is known as Designated switch or Parent switch (say switch B). The frames are forwarded to the root switch(A) through the designated switch(B). Now the lowest cost port on a switch (say switch C) is selected. This is known as the Root port. A Root Port is the port on a switch that has the lowest cost path to the Root Bridge. All Non-Root Switches will have one Root Port. Here, switch B is the designated switch for switch C and switch A is known as the root switch for switch C. Note that switch C is connected to the root switch (A) through its designated switch (B).
Spanning Tree Protocol (STP) 802.1d is used to prevent routing loops.Cisco Catalyst 5000 series switches, use BDPUs (Bridge Protocol Data Units) to determine the spanning tree topology. STP uses a Tree Algorithm (STA) to prevent loops, resulting in a stable network topology.
The following are the recommended practices for Access Layer design in an Enterprise network model:
1. Confine VLANs to one closet as much as possible to provide deterministic topology.
2. Use RPVST+ for faster convergence
3. Disable trunking on host posts, because it is not necessary.
4. Use VLAN Trunking Protocol VTP in Transparent mode
5. Consider implementing routing in the access layer to provide fast convergence and layer 3 load balancing.
Rapid Per-VLAN Spanning Tree Protocol (rapid PVST+) - Based on the IEEE 802.1w standard and has a faster convergence than STP (standard 802.1D). Rapid PVST+ includes Cisco-proprietary extensions such as BackboneFast, UplinkFast, and PortFast.
Frame-Relay: The following are true about Frame relay
1. Frame Relay is purely, a Layer 2 standard.
2. Frame Relay DLCIs have local significance.
3. Cisco supports three types of LMIs (Link Management Interface): cisco, ansi, and q933a
4. Cisco supports two types of Frame Relay encapsulation: cisco, and ietf. When you are connecting a Cisco router with a non-Cisco router, use ietf as the encapsulation method.
Cisco supports two types of Frame Relay encapsulation: cisco, and ietf. When you are connecting a Cisco router with a non-Cisco router, use ietf as the encapsulation method.
The aggregation takes place after the Access layer and before the Core layer in 3-layer approach.
HSRP: Hot Standby Router Protocol (HSRP): HSRP is a Cisco proprietary protocol that offers router redundancy. Here one router is elected as active router, and another router is elected as standby router. All other routers are put in listen HSRP state. HSRP messages are exchanges using multicast destination address 244.0.0.2 to keep a router aware of all others in the group.
The main disadvantage of HSRP and VRRP is that only one gateway is elected to be the active gateway and used to forward traffic whilst the rest are unused until the active one fails. Gateway Load Balancing Protocol (GLBP) is a Cisco proprietary protocol and performs the similar function to HSRP and VRRP but it supports load balancing among members in a GLBP group.
Note that, although we can partially configure load balancing via HSRP or VRRP using multiple groups but we have to assign different default gateways on the hosts. If one group fails, we must reconfigure the default gateways on the hosts that were earlier configured for the failed device, which results in extra administrative burden.
Virtual Router Redundancy Protocol (VRRP): VRRP is very similar to HSRP. VRRP is a standards based protocol and defined in RFC 2338. VRRP sends advertisements to multicast destination address 244.0.0.18 using IP protocol.
Gateway Load Balancing Protocol (GLBP): GLBP overcomes some of the limitations of HSRP/VRRP. Here, instead of just one active router, all routers in the group can participate and offer load balancing.
Server Load Balancing (SLB): SLB provides a virtual server IP address to which client machines can connect. The virtual server, in turn, is a group of real physical servers arranged in a server farm.
Layer2/Layer3 demarcation:
IP is used for routing packets at network layer, and not used in PC to PC communication.
IEEE 802.3 is used for communicating over Ethernet. 802.3 is a standard specification for Ethernet, a method of physical communication in a local area network (LAN. In general, 802.3 specifies the physical media and the working characteristics of Ethernet.
T1 is a digital carrier signal that transmits the DS - 1 signal. It has a data rate of about 1.544 megabits / second. E1 is similar to the T1. T1 is the North American term whereas the E1 is the European term for the transmission (digital). The data rate of E1 is about 2 mega bits per second. They are basically physical later standards.
The port number used by TCP is 6 and that of UDP is 17.
TCP is a full-duplex, connection-oriented protocol. It incorporates error checking as well.
UDP (User Datagram Protocol): UDP is a thin protocol. UDP is a connectionless protocol. It doesn't contact the destination before sending the packet and doesn't care whether the packet is reached at the destination. UDP uses port number 6. TCP and UDP work at transport layer or the Host-to-Host layer of DOD Model.
The application layer does the directory services and file transfers.
ICMP (Internet Message Control Protocol) messages are used for basic error reporting between host to host, or host to gateway. It is not used for error reporting between Gateways. ICMP messages are encapsulated using the IP protocol. For example, the command "ping" uses ICMP protocol. In the OSI Reference model, ICMPs are generally considered part of the IP layer. ICMP sends an ICMP message if the destination is unreachable. Routers can make alternate route decisions based on ICMP messages, if appropriate.
ARP (Address Resolution Protocol): IP works at network layer. IP address is a logical address. If a packet is to be delivered to a destination machine, its physical address (MAC address) needs to be known. ARP is a protocol, which enables a machine to obtain its MAC address from a know IP address.
RARP (Reverse Address Resolution Protocol): RARP is used to obtain IP address from a known MAC address.
BooTP (Bootstrap Protocol): When a diskless workstation is powered on, it broadcasts a BootP request on the network. A BooTP server responds with its IP address, Default gateway, etc.
CSMA/CD: In Carrier Sense Multiple Access With Collision Detection (CSMA/CD), a node transmits only after listening to the media, and ensuring that no transmission is taking place. Further, sending nodes detect when a collision occurs and stop transmitting immediately, backing off for a random amount of time before trying again. This results in efficient use of the media since the bandwidth of transmitting the entire frame is not wasted.
Packet-switched networks can efficiently use multiple routes inside a service provider network because the routes are formed dynamically.
Store-and-Forward switching: Here the LAN switch copies the entire frame into its buffers and computes the CRC. The frame is discarded if there are any CRC errors. Giant ( more than 1518 bytes0 and Runt (less than 64 bytes) frames are also dropped, if found.
Cut-Through (Real-Time) switching: Here, the LAN switch copies only the destination address into its buffers. It immediately looks up the switching table and starts forwarding the frame. The latency is very less because, the frame is forwarded as soon as the destination address is resolved.
CGMP: The purpose of Cisco Group Management Protocol (CGMP) and Internet Group Management Protocol (IGMP) snooping is to restrain multicast traffic in a switched network. By default, a LAN switch floods multicast traffic within the broadcast domain, and this can consume a lot of bandwidth if many multicast servers are sending streams to the segment.
CGMP enables the Cisco multicast router to understand IGMP messages sent by hosts, and informs the switch about the information contained in the IGMP packet.
With IGMP snooping, the switch intercepts IGMP messages from the host itself and updates its MAC table so that the IGMP messages are sent only to the members of the group.
