network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
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Sunday, August 12, 2012

quote of the day... qos, pbr, tos, historically...

according to odom route ocg...

an example of one of my anki cards...

Quality of service (QoS) refers to the entire process of how the network infrastructure can choose to apply different levels of service to different packets. For example, a router may need to keep delay and jitter (delay variation) low for VoIP and Video over IP packets, because these interactive voice and video calls only work well when the delay and jitter
are held very low. So, the router might let VoIP packets bypass a long queue of data packets that might be waiting to exit an interface, giving the voice packet better (lower) delay and jitter. Most QoS designs mark each packet with a different value inside the IP header, for the
purpose of identifying groups of packets–a service class–that should get a particular QoS treatment. For instance, all VoIP packets could be marked with a particular value so that the router can then find those marked bits, know that the packet is a VoIP packet due to that marking, and apply QoS accordingly. Although the most commonly used QoS marking tool today is Class-Based Marking, in the past, PBR was one of the few tools that could be used for this important QoS function
of marking packets. PBR still supports marking; however, most modern QoS designs ignore PBR’s marking capabilities.
Before discussing PBR’s marking features, a little background about the historical view of the IP header’s type of service (ToS) byte is needed. The IP header originally defined a ToS byte whose individual bits have been defined in a couple of ways over the years. One such definition used the first three bits in the ToS byte as a three-bit IP Precedence (IPP) field, which could be used for generic QoS marking, with the higher values generally implying a better QoS treatment. Back in the 1990s, the ToS byte was redefined as the Differentiated Services (DS) byte, with the first six bits defined as the Differentiated Service Code Point (DSCP). Most QoS implementations today revolve around setting the DSCP field. PBR supports setting the older QoS marking fields—the IP Precedence (IPP) and the entire ToS byte—using commands set ip precedence value and set ip tos value, respectively, in the route map. To configure packet marking, configure PBR as normal, but add a set command that defines the field to be marked and the value.

and a repost of this outstanding graphic...

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