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November 2012

IPv4 101

1. Setting an IP Address Any combination of IP-ADDR and NETMASK can be used as long as the host portion of the address is not all zeros. One exception is allowed, when using a /31 mask. By default, the router will accept combinations that result in a subnet portion of …

AutoInstall

1.AutoInstall Process The autoinstall process discribed in the following paragraphs is used in autoconfiguration of a clean router (no config) over an IP network. The following flowchart best describes this process: Here are some details about the AutoInstall steps: 1.1 Assign IP Address The first step in the AutoInstall process …

Cisco CLI Tips and Tricks

1. Key shortcuts Key Combination Result Recalling Commands Ctrl+P or UP Moves backwards through command history Ctrl+N or DOWN Moves forward through command history Moving Cursor Ctrl+B or LEFT Moves 1 character to the left (Backward) Ctrl+F or RIGHT Moves 1 character to the right (Forward) ESC,B Moves 1 word …

ARP 101

1. ARP ARP is a protocol used on broadcast networks such as Ethernet, Token Ring or FDDI that is used to map L3 Addresses (like IP) to layer 2 Addresses (like Ethernet MAC). When a host needs to send traffic to another host, it knows its Layer 3 address, but …

DNS 101

1. Defining hosts and domains locally To define a static host name to address mapping, use the following command: For hosts that are accessed without a domain name at the end, (hostname.domain-name), you can define a default domain name or a list of domain names to be used, using one …

WCCP 101

WCCP support on Cisco router is a feature used to intercept traffic (usually HTTP requests) and redirect it to a cluster of content engines. This feature is mainly used for webcaching or WAAS implementations. The WCCP protocol is a control protocol used by router and Content Engines to communicate with …

RSVP 101

1. RSVP Basics RSVP (Resource Reservation Protocol) is an industry standard protocol used to implement IntServ QoS architecture. RSVP is used by the sender to request a certain QoS level from the routers along the path to the receiver. Devices along the way should be RSVP aware and they will …

Header and Payload Compression

1. Header Compression (RTP,TCP) Header compression works by creating a context on both sides of a connection for each TCP/RTP data stream. The context contains header information for the stream so that data doesn’t need to be sent with every packet. For RTP, you can also send full headers periodically …

SPD – Selective Packet Discard

SPD is a feature that allows prioritisation of the Input Queue. Normally, the Input Queue only allows FIFO scheduling. With SPD enabled, 2 additional queues are created, the SPD Headroom and the SPD Extended Headroom. Layer 2 keepalives and IGP packets are allowed to be enqueued in any of the …

QoS 101

1. Congestion, Delay, Jitter Congestion occurs when there is more traffic to be sent than the interface can physically send. Depending on the configuration, packets that are waiting to be sent can be dropped or queued. Dropping is no good because the information is lost (UDP) or it may require …