Cisco

With the low cost of general purpose central processing units, the price of software based routers is become more affordable at the expensive of total packet throughput. When a route processor (RP) is equipped with a forwarding engine so it can make all of the packet switching decisions, this is known as a centralised forwarding…

A platforms TCAM allows for the matching and evaluation of a packet on more than one field. TCAM is an extension of the content addressable memory (CAM) architecutre but is enhanced to allow for upper layer procerssing such as identifying the Layer 2 and 3 source and destination addresses, protocol, QoS markings and more. TCAM…

A Cisco proprietary switching mechanism, Cisco Express Forwarding has been the default switching mechanism on most Cisco platforms that do all their packet switching and forwarding using the general purpose CPU since the 1990s, and is the default switching mechanism used by all Cisco platforms that use specialised ASICs and Network Processing Units (NPUs) for…

Process switching can also be referred to as software switching or slow path switching. Process switching is when the general central processing unit (rather than any dedicated ASIC chip) takes charge of packet switching on the hardware device. Within Cisco IOS the process ip_input runs on the general CPU for incoming network packets that can…

In the beginning Cisco routers on recieving a packet would remove the Layer 2 information and verify that the route existed for the destination address on that packet. If a matching route could not be found on the router, the packet would be dropped. Otherwise if a matching route was found, new Layer 2 information…

On a Cisco device, IPv4 addresses configured can be viewed with the command show ip interface with the optional suffix of brief or a specific interface-id. The brief suffix shows a summarised view of the configured IP addresses on the device. The standard command can show a large amount of information such as the configured…

TCP/IP is the standard protocol for most networks. To begin with it was used with IPv4 (Internet Protocol Version 4) and it’s 32-bit IP addressing. IPv4s public IP address pool over the years has become exhausted with no longer any fresh spare IP addressing space to be given out. Options to get IPv4 address space…

Layer 3 forwarding can be broken down into two types: Forwarding traffic to devices within the same subnet Forwarding traffic to devices on a different subnet Forwarding to devices within the same subnet Two devices that wish to communicate on the same subnet can do so locally. As the source device begins to form the…

MAC Address Table The MAC addres table keeps a record of the switch ports and VLANs to which a network host is associated too. The switch builds its MAC address table by keeping track of the source MAC addresses of packets that it recieves through its ports. The information that the switch collects from these…

Trunk ports can carry multiple VLANs across a single port. Trunk ports are typically used when uplinking a multiple number of VLANs togerther from one network hardware device to another such as a switch or router over a single port to port connection. Switch ports on a Cisco Catalyst switch are configured with the command…